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7 Jan 2013

Volume 138, Issue 1, Articles (01xxxx)

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J. Chem. Phys. 138, 014101 (2013); http://dx.doi.org/10.1063/1.4770502 (12 pages)

Simon A. Maurer, Daniel S. Lambrecht, Jörg Kussmann, and Christian Ochsenfeld
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Communication: A six-dimensional state-to-state quantum dynamics study of the H + CH4 → H2 + CH3 reaction (J = 0)

Shu Liu, Jun Chen, Zhaojun Zhang, and Dong H. Zhang

J. Chem. Phys. 138, 011101 (2013); http://dx.doi.org/10.1063/1.4774116 (4 pages) | Cited 2 times

Online Publication Date: 3 January 2013

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We report a quantum state-to-state reaction dynamics study for the title reaction. The calculation was based on an approximation that we introduced to the eight-dimensional model for the X + YCZ3 → XY + CZ3 type of reactions that restricts the non-reacting CZ3 group in C3V symmetry proposed by Palma and Clary [J. Chem. Phys. 112, 1859 (2000)10.1063/1.480749], by assuming that the CZ3 group can rotate freely with respect to its C3V symmetry axis. With the CH bond length in group fixed at its equilibrium distance, the degree of freedom included in the calculation was reduced to six. Our calculation shows that the six-dimensional treatment can produce reaction probabilities essentially indistinguishable from the seven-dimensional (with CH bond length fixed in the original eight-dimensional model) results. The product vibrational/rotational state distributions and product energy partitioning information are presented for ground initial rovibrational state with the total angular momentum J = 0.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
82.20.-w Chemical kinetics and dynamics
82.20.Ej Quantum theory of reaction cross section
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back to top Theoretical Methods and Algorithms

Efficient distance-including integral screening in linear-scaling Møller-Plesset perturbation theory

Simon A. Maurer, Daniel S. Lambrecht, Jörg Kussmann, and Christian Ochsenfeld

J. Chem. Phys. 138, 014101 (2013); http://dx.doi.org/10.1063/1.4770502 (12 pages) | Cited 1 time

Online Publication Date: 2 January 2013

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Efficient estimates for the preselection of two-electron integrals in atomic-orbital based Møller-Plesset perturbation theory (AO-MP2) theory are presented, which allow for evaluating the AO-MP2 energy with computational effort that scales linear with molecular size for systems with a significant HOMO-LUMO gap. The estimates are based on our recently introduced QQR approach [S. A. Maurer, D. S. Lambrecht, D. Flaig, and C. Ochsenfeld, J. Chem. Phys. 136, 144107 (2012)10.1063/1.3693908], which exploits the asympotic decay of the integral values with increasing bra-ket separation as deduced from the multipole expansion and combines this decay behavior with the common Schwarz bound to a tight and simple estimate. We demonstrate on a diverse selection of benchmark systems that our AO-MP2 method in combination with the QQR-type estimates produces reliable results for systems with both localized and delocalized electronic structure, while in the latter case the screening essentially reverts to the common Schwarz screening. For systems with localized electronic structure, our AO-MP2 method shows an early onset of linear scaling as demonstrated on DNA systems. The favorable scaling behavior allows to compute systems with more than 1000 atoms and 10 000 basis functions on a single core that are clearly not accessible with conventional MP2 methods. Furthermore, our AO-MP2 method is particularly suited for parallelization and we present benchmark calculations on a protein-DNA repair complex comprising 2025 atoms and 20 371 basis functions.
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31.15.xp Perturbation theory
87.14.gk DNA
36.20.-r Macromolecules and polymer molecules

Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: Insights from an analytically solvable model

Dmitrii E. Makarov

J. Chem. Phys. 138, 014102 (2013); http://dx.doi.org/10.1063/1.4773283 (10 pages)

Online Publication Date: 2 January 2013

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Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers’ theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and “internal” friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which—unlike Kramers’ theory—account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.
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87.15.La Mechanical properties
87.14.ej Enzymes
87.15.kr Protein-solvent interactions
87.15.R- Reactions and kinetics
87.15.Zg Phase transitions
87.15.Cc Folding: thermodynamics, statistical mechanics, models, and pathways

The flexible nature of exchange, correlation, and Hartree physics: Resolving “delocalization” errors in a “correlation free” density functional

Tim Gould and John F. Dobson

J. Chem. Phys. 138, 014103 (2013); http://dx.doi.org/10.1063/1.4773284 (7 pages) | Cited 1 time

Online Publication Date: 3 January 2013

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By exploiting freedoms in the definitions of “correlation,” “exchange,” and “Hartree” physics in ensemble systems, we better generalise the notion of “exact exchange” (EXX) to systems with fractional occupations of the frontier orbitals, arising in the dissociation limit of some molecules. We introduce the linear EXX (“LEXX”) theory whose pair distribution and energy are explicitly piecewise linear in the occupations fiσ. We provide explicit expressions for these functions for frontier s and p shells. Used in an optimised effective potential (OEP) approach the LEXX yields energies bounded by the piecewise linear “ensemble EXX” (EEXX) energy and standard fractional optimised EXX energy: EEEXX ⩽ ELEXX ⩽ EEXX. Analysis of the LEXX explains the success of standard OEP methods for diatoms at large spacing, and why they can fail when both spins are allowed to be non-integer so that “ghost” Hartree interactions appear between opposite spin electrons in the usual formula. The energy ELEXX contains a cancellation term for the spin ghost case. It is evaluated for H, Li, and Na fractional ions with clear derivative discontinuities for all cases. The p-shell form reproduces accurate correlation-free energies of B-F and Al-Cl. We further test LEXX plus correlation energy calculations on fractional ions of C and F and again we find both derivative discontinuities and good agreement with exact results.
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31.15.xr Self-consistent-field methods
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.V- Electron correlation calculations for atoms, ions and molecules

A wavelet analysis for the X-ray absorption spectra of molecules

T. J. Penfold, I. Tavernelli, C. J. Milne, M. Reinhard, A. El Nahhas, R. Abela, U. Rothlisberger, and M. Chergui

J. Chem. Phys. 138, 014104 (2013); http://dx.doi.org/10.1063/1.4772766 (7 pages) | Cited 2 times

Online Publication Date: 3 January 2013

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We present a Wavelet transform analysis for the X-ray absorption spectra of molecules. In contrast to the traditionally used Fourier transform approach, this analysis yields a 2D correlation plot in both R- and k-space. As a consequence, it is possible to distinguish between different scattering pathways at the same distance from the absorbing atom and between the contributions of single and multiple scattering events, making an unambiguous assignment of the fine structure oscillations for complex systems possible. We apply this to two previously studied transition metal complexes, namely iron hexacyanide in both its ferric and ferrous form, and a rhenium diimine complex, [ReX(CO)3(bpy)], where X = Br, Cl, or ethyl pyridine (Etpy). Our results demonstrate the potential advantages of using this approach and they highlight the importance of multiple scattering, and specifically the focusing phenomenon to the extended X-ray absorption fine structure (EXAFS) spectra of these complexes. We also shed light on the low sensitivity of the EXAFS spectrum to the Re-X scattering pathway.
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33.20.Rm X-ray spectra
31.15.E- Density-functional theory
33.15.Pw Fine and hyperfine structure

Exploiting a semi-analytic approach to study first order phase transitions

Carlos. E. Fiore and M. G. E. da Luz

J. Chem. Phys. 138, 014105 (2013); http://dx.doi.org/10.1063/1.4772809 (11 pages)

Online Publication Date: 3 January 2013

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In a previous contribution [C. E. Fiore and M. G. E. da Luz, Phys. Rev. Lett. 107, 230601 (2011)10.1103/PhysRevLett.107.230601] we have proposed a method to treat first order phase transitions at low temperatures. It describes arbitrary order parameter through an analytical expression W, which depends on few coefficients. Such coefficients can be calculated by simulating relatively small systems, hence, with a low computational cost. The method determines the precise location of coexistence lines and arbitrary response functions (from proper derivatives of W). Here we exploit and extend the approach, discussing a more general condition for its validity. We show that, in fact, it works beyond the low T limit, provided the first order phase transition is strong enough. Thus, W can be used even to study athermal problems, as exemplified for a hard-core lattice gas. We furthermore demonstrate that other relevant thermodynamic quantities, as entropy and energy, are also obtained from W. To clarify some important mathematical features of the method, we analyze in detail an analytically solvable problem. Finally, we discuss different representative models, namely, Potts, Bell-Lavis, and associating gas-lattice, illustrating the procedure's broad applicability.
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05.70.Fh Phase transitions: general studies
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)
05.70.Ce Thermodynamic functions and equations of state

Linear scaling explicitly correlated MP2-F12 and ONIOM methods for the long-range interactions of the nanoscale clusters in methanol aqueous solutions

Wei Li

J. Chem. Phys. 138, 014106 (2013); http://dx.doi.org/10.1063/1.4773011 (9 pages) | Cited 1 time

Online Publication Date: 3 January 2013

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A linear scaling quantum chemistry method, generalized energy-based fragmentation (GEBF) approach has been extended to the explicitly correlated second-order Møller-Plesset perturbation theory F12 (MP2-F12) method and own N-layer integrated molecular orbital molecular mechanics (ONIOM) method, in which GEBF-MP2-F12, GEBF-MP2, and conventional density functional tight-binding methods could be used for different layers. Then the long-range interactions in dilute methanol aqueous solutions are studied by computing the binding energies between methanol molecule and water molecules in gas-phase and condensed phase methanol-water clusters with various sizes, which were taken from classic molecular dynamics (MD) snapshots. By comparing with the results of force field methods, including SPC, TIP3P, PCFF, and AMOEBA09, the GEBF-MP2-F12 and GEBF-ONIOM methods are shown to be powerful and efficient for studying the long-range interactions at a high level. With the GEBF-ONIOM(MP2-F12:MP2) and GEBF-ONIOM(MP2-F12:MP2:cDFTB) methods, the diameters of the largest nanoscale clusters under studies are about 2.4 nm (747 atoms and 10 209 basis functions with aug-cc-pVDZ basis set) and 4 nm (3351 atoms), respectively, which are almost impossible to be treated by conventional MP2 or MP2-F12 method. Thus, the GEBF-F12 and GEBF-ONIOM methods are expected to be a practical tool for studying the nanoscale clusters in condensed phase, providing an alternative benchmark for ab initio and density functional theory studies, and developing new force fields by combining with classic MD simulations.
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36.40.Jn Reactivity of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.aq Strongly correlated electron systems: generalized tight-binding method
31.15.E- Density-functional theory
31.15.xp Perturbation theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Polarization consistent basis sets. VIII. The transition metals Sc-Zn

Frank Jensen

J. Chem. Phys. 138, 014107 (2013); http://dx.doi.org/10.1063/1.4773017 (7 pages)

Online Publication Date: 3 January 2013

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Polarization consistent basis sets, optimized for density functional calculations, are proposed for the transition metals Sc-Zn. The basis set composition in terms of number of primitive functions and the contraction is defined based on energetic analyses of atoms and molecules along the lines used in previous work and on the performance for molecular systems. The performance for atomization energies and dipole moments is compared to other widely used basis sets, and it is shown that the new basis sets allow a systematic reduction of basis set errors and, in general, have basis set errors lower than or at par with existing ones.
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31.15.E- Density-functional theory
32.30.-r Atomic spectra
32.50.+d Fluorescence, phosphorescence (including quenching)

The multigrid POTFIT (MGPF) method: Grid representations of potentials for quantum dynamics of large systems

Daniel Peláez and Hans-Dieter Meyer

J. Chem. Phys. 138, 014108 (2013); http://dx.doi.org/10.1063/1.4773021 (16 pages)

Online Publication Date: 3 January 2013

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In this article, a new method, multigrid POTFIT (MGPF), is presented. MGPF is a grid-based algorithm which transforms a general potential energy surface into product form, that is, a sum of products of one-dimensional functions. This form is necessary to profit from the computationally advantageous multiconfiguration time-dependent Hartree method for quantum dynamics. MGPF circumvents the dimensionality related issues present in POTFIT [A. Jäckle and H.-D. Meyer, J. Chem. Phys. 104, 7974 (1996)10.1063/1.471513], allowing quantum dynamical studies of systems up to about 12 dimensions. MGPF requires the definition of a fine grid and a coarse grid, the latter being a subset of the former. The MGPF approximation relies on a series of underlying POTFIT calculations on grids which are smaller than the fine one and larger than or equal to the coarse one. This aspect makes MGPF a bit less accurate than POTFIT but orders of magnitude faster and orders of magnitude less memory demanding than POTFIT. Moreover, like POTFIT, MGPF is variational and provides an efficient error control.
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31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces

Electron affinities and ionisation potentials for atoms via “benchmark” tdDFT calculations with and without exchange kernels

Tim Gould and John F. Dobson

J. Chem. Phys. 138, 014109 (2013); http://dx.doi.org/10.1063/1.4773066 (5 pages) | Cited 1 time

Online Publication Date: 3 January 2013

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One of the known weaknesses of the adiabatic connection fluctuation dissipation (ACFD) correlation energy functional under the direct random-phase approximation (RPA) is its failure to accurately predict energy differences between dissimilar systems. In this work we evaluate ionisation potentials I and electron affinities A for atoms and ions with one to eighteen electrons using the ACFD functional under the RPA, and with the “PGG (Petersilka-Gossmann-Gross)” and “RXH (radial exchange hole)” model exchange kernels. All calculations are carried out using a real-space, all electron method with an exact exchange groundstate to minimise errors. As expected, the RPA is less accurate even than some regular density functional theory approaches, while the introduction of a dynamical exchange kernel improves results. In contrast to the case of atomic groundstate energies, the PGG kernel outperforms the RXH kernel for I and A. Mean absolute errors for I/A are found to be 3.27/2.38 kcal/mol, 4.38/5.43 kcal/mol, and 9.24/ 8.94 kcal/mol for the PGG, RXH, and RPA, respectively. We thus show that the inclusion of even the simple “RXH” kernel improves both quantities when compared to the RPA.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
32.50.+d Fluorescence, phosphorescence (including quenching)

Efficient methods for including quantum effects in Monte Carlo calculations of large systems: Extension of the displaced points path integral method and other effective potential methods to calculate properties and distributions

Steven L. Mielke, Mohammadhasan Dinpajooh, J. Ilja Siepmann, and Donald G. Truhlar

J. Chem. Phys. 138, 014110 (2013); http://dx.doi.org/10.1063/1.4772667 (15 pages)

Online Publication Date: 4 January 2013

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We present a procedure to calculate ensemble averages, thermodynamic derivatives, and coordinate distributions by effective classical potential methods. In particular, we consider the displaced-points path integral (DPPI) method, which yields exact quantal partition functions and ensemble averages for a harmonic potential and approximate quantal ones for general potentials, and we discuss the implementation of the new procedure in two Monte Carlo simulation codes, one that uses uncorrelated samples to calculate absolute free energies, and another that employs Metropolis sampling to calculate relative free energies. The results of the new DPPI method are compared to those from accurate path integral calculations as well as to results of two other effective classical potential schemes for the case of an isolated water molecule. In addition to the partition function, we consider the heat capacity and expectation values of the energy, the potential energy, the bond angle, and the OH distance. We also consider coordinate distributions. The DPPI scheme performs best among the three effective potential schemes considered and achieves very good accuracy for all of the properties considered. A key advantage of the effective potential schemes is that they display much lower statistical sampling variances than those for accurate path integral calculations. The method presented here shows great promise for including quantum effects in calculations on large systems.
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03.65.Yz Decoherence; open systems; quantum statistical methods
02.50.Ng Distribution theory and Monte Carlo studies
05.70.Ce Thermodynamic functions and equations of state
33.15.Dj Interatomic distances and angles
02.70.Rr General statistical methods

Non-Markovian stochastic Schrödinger equation at finite temperatures for charge carrier dynamics in organic crystals

Xinxin Zhong and Yi Zhao

J. Chem. Phys. 138, 014111 (2013); http://dx.doi.org/10.1063/1.4773319 (9 pages)

Online Publication Date: 7 January 2013

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A new non-Markovian stochastic Schrödinger equation at finite temperatures is presented to correctly describe charge carrier dynamics in organic molecular crystals. The electron-phonon interactions in both site energies and electronic couplings are incorporated by the time-dependent complex-valued random fluctuations which are generated from corresponding spectral density functions. The approach is thus easily extended to investigate coherent-to-hopping charge transfer in systems with thousands of molecular sites. The capability of present approach is demonstrated by numerical simulations of carrier dynamics in the spin-boson model and a realistic Fenna-Matthews-Olson complex. The results manifest that the non-Markovian effect and complex-valued random forces are essential to guarantee the detailed balance. In an application to a long-chain donor-acceptor system, it is also interesting to find a property of coherent-to-hopping charge transfer from temperature dependence of diffusion coefficients.
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63.20.kd Phonon-electron interactions
66.30.J- Diffusion of impurities
02.50.Ga Markov processes
05.30.Jp Boson systems
72.20.Ee Mobility edges; hopping transport

Efficient methods and practical guidelines for simulating isotope effects

Michele Ceriotti and Thomas E. Markland

J. Chem. Phys. 138, 014112 (2013); http://dx.doi.org/10.1063/1.4772676 (13 pages) | Cited 1 time

Online Publication Date: 7 January 2013

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The shift in chemical equilibria due to isotope substitution is frequently exploited to obtain insight into a wide variety of chemical and physical processes. It is a purely quantum mechanical effect, which can be computed exactly using simulations based on the path integral formalism. Here we discuss how these techniques can be made dramatically more efficient, and how they ultimately outperform quasi-harmonic approximations to treat quantum liquids not only in terms of accuracy, but also in terms of computational cost. To achieve this goal we introduce path integral quantum mechanics estimators based on free energy perturbation, which enable the evaluation of isotope effects using only a single path integral molecular dynamics trajectory of the naturally abundant isotope. We use as an example the calculation of the free energy change associated with H/D and 16O/18O substitutions in liquid water, and of the fractionation of those isotopes between the liquid and the vapor phase. In doing so, we demonstrate and discuss quantitatively the relative benefits of each approach, thereby providing a set of guidelines that should facilitate the choice of the most appropriate method in different, commonly encountered scenarios. The efficiency of the estimators we introduce and the analysis that we perform should in particular facilitate accurate ab initio calculation of isotope effects in condensed phase systems.
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31.30.Gs Hyperfine interactions and isotope effects
82.20.Tr Kinetic isotope effects including muonium
82.60.Hc Chemical equilibria and equilibrium constants
back to top Advanced Experimental Techniques

The vibrational spectrum of CaCO3 aragonite: A combined experimental and quantum-mechanical investigation

Cédric Carteret, Marco De La Pierre, Manuel Dossot, Fabien Pascale, Alessandro Erba, and Roberto Dovesi

J. Chem. Phys. 138, 014201 (2013); http://dx.doi.org/10.1063/1.4772960 (12 pages) | Cited 1 time

Online Publication Date: 4 January 2013

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The vibrational properties of CaCO3 aragonite have been investigated both theoretically, by using a quantum mechanical approach (all electron Gaussian type basis set and B3LYP HF-DFT hybrid functional, as implemented in the CRYSTAL code) and experimentally, by collecting polarized infrared (IR) reflectance and Raman spectra. The combined use of theory and experiment permits on the one hand to analyze the many subtle features of the measured spectra, on the other hand to evidentiate limits and deficiencies of both approaches. The full set of TO and LO IR active modes, their intensities, the dielectric tensor (in its static and high frequency components), and the optical indices have been determined, as well as the Raman frequencies. Tools such as isotopic substitution and graphical animation of the modes are available, that complement the analysis of the spectrum.
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63.20.-e Phonons in crystal lattices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
back to top Atoms, Molecules, and Clusters

Chirped-pulse millimeter-wave spectroscopy: Spectrum, dynamics, and manipulation of Rydberg–Rydberg transitions

Anthony P. Colombo, Yan Zhou, Kirill Prozument, Stephen L. Coy, and Robert W. Field

J. Chem. Phys. 138, 014301 (2013); http://dx.doi.org/10.1063/1.4772762 (9 pages)

Online Publication Date: 2 January 2013

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We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg–Rydberg transitions is that they have enormous electric dipole transition moments (∼5 kiloDebye at n* ∼ 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70–84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is ∼100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.
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32.30.Bv Radio-frequency, microwave, and infrared spectra
32.70.Cs Oscillator strengths, lifetimes, transition moments
32.80.Ee Rydberg states
32.30.-r Atomic spectra

Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels

En-Lan Hu, Po-Yu Tsai, He Fan, and King-Chuen Lin

J. Chem. Phys. 138, 014302 (2013); http://dx.doi.org/10.1063/1.4768872 (10 pages)

Online Publication Date: 2 January 2013

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Upon one-photon excitation at 248 nm, gaseous CH3C(O)SH is dissociated following three pathways with the products of (1) OCS + CH4, (2) CH3SH + CO, and (3) CH2CO + H2S that are detected using time-resolved Fourier-transform infrared emission spectroscopy. The excited state 1(nO, π*CO) has a radiative lifetime of 249 ± 11 ns long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of collision-induced internal conversion is estimated to be 1.1 × 10−10 cm3 molecule−1 s−1. Among the primary dissociation products, a fraction of the CH2CO moiety may undergo further decomposition to CH2 + CO, of which CH2 is confirmed by reaction with O2 producing CO2, CO, OH, and H2CO. Such a secondary decomposition was not observed previously in the Ar matrix-isolated experiments. The high-resolution spectra of CO are analyzed to determine the ro-vibrational energy deposition of 8.7 ± 0.7 kcal/mol, while the remaining primary products with smaller rotational constants are recognized but cannot be spectrally resolved. The CO fragment detected is mainly ascribed to the primary production. A prior distribution method is applied to predict the vibrational distribution of CO that is consistent with the experimental findings.
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82.50.Bc Processes caused by infrared radiation
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Correlation between the variation in observed melting temperatures and structural motifs of the global minima of gallium clusters: An ab initio study

Anju Susan, Aniruddha Kibey, Vaibhav Kaware, and Kavita Joshi

J. Chem. Phys. 138, 014303 (2013); http://dx.doi.org/10.1063/1.4772470 (7 pages)

Online Publication Date: 3 January 2013

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We have investigated the correlation between the variation in the melting temperature and the growth pattern of small positively charged gallium clusters. Significant shift in the melting temperatures was observed for a change of only few atoms in the size of the cluster. Clusters with size between 31−42 atoms melt between 500–600 K whereas those with 46−48 atoms melt around 800 K. Density functional theory based first principles simulations have been carried out on Ga n+ clusters with n = 31, …, 48. At least 150 geometry optimizations have been performed towards the search for the global minima for each size resulting in about 3000 geometry optimizations. For gallium clusters in this size range, the emergence of spherical structures as the ground state leads to higher melting temperature. The well-separated core and surface shells in these clusters delay isomerization, which results in the enhanced stability of these clusters at elevated temperatures. The observed variation in the melting temperature of these clusters therefore has a structural origin.
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64.70.dj Melting of specific substances
61.66.Bi Elemental solids
71.15.-m Methods of electronic structure calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
82.30.Qt Isomerization and rearrangement

Correlated ab initio investigations on the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O2−(X2Πg)− HF (X1Σ+) complex

Wafaa M. Fawzy, Mahmoud Elsayed, and Yuchen Zhang

J. Chem. Phys. 138, 014304 (2013); http://dx.doi.org/10.1063/1.4772653 (10 pages)

Online Publication Date: 3 January 2013

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This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O2−(X2Πg)− HF (X1Σ+) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2–5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and Cs symmetry along the A″ surface of the complex, whereas the A′ surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-De) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and De value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C2v symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm−1. The calculated harmonic oscillator vibrational frequencies showed that the H–F stretch vibrational transition in the complex is redshifted by 2564 cm−1 and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O2−− HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.50.Bc Potential energy surfaces for ground electronic states
31.15.bw Coupled-cluster theory
31.15.ae Electronic structure and bonding characteristics
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry

Interatomic decay of inner-valence ionized states in ArXe clusters: Relativistic approach

Elke Fasshauer, Markus Pernpointner, and Kirill Gokhberg

J. Chem. Phys. 138, 014305 (2013); http://dx.doi.org/10.1063/1.4772654 (10 pages)

Online Publication Date: 3 January 2013

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In this work we investigate interatomic electronic decay processes taking place in mixed argon-xenon clusters upon the inner-valence ionization of an argon center. We demonstrate that both interatomic Coulombic decay and electron-transfer mediated decay (ETMD) are important in larger rare gas clusters as opposed to dimers. Calculated secondary electron spectra are shown to depend strongly on the spin-orbit coupling in the final states of the decay as well as the presence of polarizable environment. It follows from our calculations that ETMD is a pure interface process taking place between the argon-xenon layers. The interplay of all these effects is investigated in order to arrive at a suitable physical model for the decay of inner-valence vacancies taking place in mixed ArXe clusters.
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36.40.Mr Spectroscopy and geometrical structure of clusters
32.80.Aa Inner-shell excitation and ionization
34.80.-i Electron and positron scattering
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

DFT study of vibronic properties of d8 (Ni-, Pd-, and Pt-) phthalocyanines

D. Pouladsaz, M. Schreiber, and T. G. Gopakumar

J. Chem. Phys. 138, 014306 (2013); http://dx.doi.org/10.1063/1.4773014 (6 pages)

Online Publication Date: 3 January 2013

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By means of density functional theory, we have studied the electronic structure and vibronic properties of single neutral NiPc, PdPc, and PtPc molecules and their singly and doubly ionized cations and anions. In particular, the vibronic couplings and reorganization energies of all systems are compared. Partitioning of the reorganization energy, corresponding to the photoelectron spectra of the first and second ionizations of studied molecules, into normal mode contributions shows that the major contributions are due to several vibrational modes with a1g symmetry and energies lower than 1600 cm−1. The results reveal that the reorganization energy due to the singly positive ionization in the studied molecules is up to about one order of magnitude less than other reorganization energies. This makes these metal phthalocyanines, from the perspective of intramolecular reorganization energies, attractive as electron donor for intramolecular electron transfer in electron acceptor-donor systems.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
34.50.Gb Electronic excitation and ionization of molecules
31.15.E- Density-functional theory
33.60.+q Photoelectron spectra

Spectroscopic and thermochemical properties of the c-C6H7 radical: A high-level theoretical study

Arne Bargholz, Rainer Oswald, and Peter Botschwina

J. Chem. Phys. 138, 014307 (2013); http://dx.doi.org/10.1063/1.4773015 (8 pages)

Online Publication Date: 3 January 2013

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The electronic ground state (math2B1) of the cyclohexadienyl radical (c-C6H7) has been studied by explicitly correlated coupled cluster theory at the RCCSD(T)-F12x (x = a, b) level, partly in combination with the double-hybrid density functional method B2PLYP. An accurate equilibrium structure has been established and the ground-state rotational constants are predicted to be A0 = 5347.3 MHz, B0 = 5249.7 MHz, and C0 = 2692.5 MHz. The calculated vibrational wavenumbers agree well with the recent p-H2 matrix IR data [M. Bahou, Y.-J. Wu, and Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012)10.1063/1.3703502] and several predictions have been made. A low value of 6.803 ± 0.005 eV is predicted for the adiabatic ionization energy of c-C6H7. Owing to a moderately large change in the equilibrium structure upon ionization, the first band of the photoelectron spectrum is dominated by the adiabatic peak (100%) and only the peaks corresponding to excitation of the two lowest totally symmetric vibrations (ν12 and ν11) by one vibrational quantum have relative intensities of more than 15%. The C6H6-H dissociation energy is calculated to be D0 = 85.7 kJ mol−1, with an estimated error of ∼2 kJ mol−1.
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82.60.Cx Enthalpies of combustion, reaction, and formation
31.15.bw Coupled-cluster theory
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.vj Electron correlation calculations for atoms and ions: excited states
33.60.+q Photoelectron spectra
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

The electronic structure of gas phase croconic acid compared to the condensed phase: More insight into the hydrogen bond interaction

F. Bisti, A. Stroppa, F. Perrozzi, M. Donarelli, S. Picozzi, M. Coreno, M. de Simone, K. C. Prince, and L. Ottaviano

J. Chem. Phys. 138, 014308 (2013); http://dx.doi.org/10.1063/1.4773059 (4 pages) | Cited 1 time

Online Publication Date: 3 January 2013

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The electronic structure of croconic acid in the gas phase has been investigated by means of core level and valence band photoemission spectroscopy and compared with hybrid Heyd-Scuseria-Ernzerhof density functional theory calculations. The results have been compared with the corresponding ones of the condensed phase. In the gas phase, due to the absence of hydrogen bond intermolecular interactions, the O 1 s core level spectrum shows a shift of binding energy between the hydroxyl (O–H) and the carbonyl group (C=O) of 2.1  eV, which is larger than the condensed phase value of 1.6  eV. Interestingly, such a shift decreases exponentially with the increase of the O–H distance calculated from theory. The significant differences between the gas and condensed phase valence band spectra highlight the important role played by the hydrogen bonding in shaping the electronic structure of the condensed phase.
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33.60.+q Photoelectron spectra
33.15.Fm Bond strengths, dissociation energies
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.E- Density-functional theory

The potential energy function of the ground electronic state of 16O2

Photos G. Hajigeorgiou

J. Chem. Phys. 138, 014309 (2013); http://dx.doi.org/10.1063/1.4773285 (8 pages)

Online Publication Date: 7 January 2013

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The potential energy function of the ground X 3Σg− electronic state of 16O2 has been obtained in analytical form by employing a fully quantum-mechanical direct potential fitting method. Term values generated from highly precise Dunham coefficients were employed in the direct fit, yielding a potential energy function that is accurate up to υ = 31, or up to an energy that is 90% of the dissociation limit. The term values are represented with a standard deviation of 0.0031 cm−1 by the quantum-mechanical eigenvalues of the derived potential energy function. There is considerable evidence for N-dependent nonadiabatic coupling between the ground X 3Σg− electronic state and the b 1Σg+ excited electronic state.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
02.10.Ud Linear algebra
33.20.Sn Rotational analysis

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters

Meng Zhang, Jing Zhao, Jinxiang Liu, Lianwen Zhou, and Yuxiang Bu

J. Chem. Phys. 138, 014310 (2013); http://dx.doi.org/10.1063/1.4773398 (11 pages)

Online Publication Date: 7 January 2013

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We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the π⋯HO interactions in the neutral Bz(H2O)n (n = 1–8) clusters, and the size of the water cluster does not influence the nature of its interaction with the π system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (π*) of the Bz ring, and the π⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H–O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C–H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak π⋯HO interaction plays an important role as the driving force in conversion of the two states.
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36.40.Cg Electronic and magnetic properties of clusters
31.15.ae Electronic structure and bonding characteristics
31.15.xv Molecular dynamics and other numerical methods
33.15.Fm Bond strengths, dissociation energies

Current rectification in nickelocenylferrocene sandwiched between two gold electrodes

Yukihito Matsuura

J. Chem. Phys. 138, 014311 (2013); http://dx.doi.org/10.1063/1.4773404 (4 pages)

Online Publication Date: 7 January 2013

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I present a theoretical study of the electronic transport properties of nickelocenylferrocene sandwiched between gold electrodes. Compared with the biferrocene system, the nickelocenylferrocene system had high electrical conduction and rectification in the bias range −1 to 1 V. Furthermore, the spin-down states of the nickelocenylferrocene system exhibited perfect spin-filtering properties. From the electronic states of the nickelocenylferrocene, it was found that the rectification was caused by a difference in the bias-dependent behaviors between the Fe 3d and Ni 3d orbitals.
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73.40.Ei Rectification
72.80.Le Polymers; organic compounds (including organic semiconductors)
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