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7 Jun 2011

Volume 134, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 134, 214501 (2011); http://dx.doi.org/10.1063/1.3594115 (7 pages)

Kiseok Chang, Eunja Kim, Philippe F. Weck, and David Tománek
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Communication: Determination of the bond dissociation energy (D0) of the water dimer, (H2O)2, by velocity map imaging

Blithe E. Rocher-Casterline, Lee C. Ch'ng, Andrew K. Mollner, and Hanna Reisler

J. Chem. Phys. 134, 211101 (2011); http://dx.doi.org/10.1063/1.3598339 (4 pages) | Cited 5 times

Online Publication Date: 1 June 2011

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The bond dissociation energy (D0) of the water dimer is determined by using state-to-state vibrational predissociation measurements following excitation of the bound OH stretch fundamental of the donor unit of the dimer. Velocity map imaging and resonance-enhanced multiphoton ionization (REMPI) are used to determine pair-correlated product velocity and translational energy distributions. H2O fragments are detected in the ground vibrational (000) and the first excited bending (010) states by 2 + 1 REMPI via the math 1B1 (000) ← math 1A1 (000 and 010) transitions. The fragments’ velocity and center-of-mass translational energy distributions are determined from images of selected rovibrational levels of H2O. An accurate value for D0 is obtained by fitting both the structure in the images and the maximum velocity of the fragments. This value, D0 = 1105 ± 10 cm−1 (13.2 ± 0.12 kJ/mol), is in excellent agreement with the recent theoretical value of D0 = 1103 ± 4 cm−1 (13.2 ± 0.05 kJ/mol) suggested as a benchmark by Shank et al. [J. Chem. Phys. 130, 144314 (2009)].
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.80.Eh Autoionization, photoionization, and photodetachment
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back to top Theoretical Methods and Algorithms

Magnetic exchange couplings evaluated with Rung 3.5 density functionals

Jordan J. Phillips, Juan E. Peralta, and Benjamin G. Janesko

J. Chem. Phys. 134, 214101 (2011); http://dx.doi.org/10.1063/1.3596070 (7 pages) | Cited 1 time

Online Publication Date: 1 June 2011

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Rung 3.5 exchange-correlation functionals are assessed for the calculation of magnetic exchange coupling parameters and atomic spin populations for a variety of inorganic and organic magnetic systems. Density functional theory calculations of exchange couplings sensitively depend on nonlocal contributions to the exchange-correlation functional. Semilocal functionals, Rungs 1-3 on “Jacob's Ladder” of density functional approximations, yield excessively delocalized electrons and overestimated absolute exchange couplings. Fourth-rung hybrid functionals admixing nonlocal exchange improve the results. We show that new “Rung 3.5” functionals give magnetic properties intermediate between semilocal and hybrid functionals, providing additional evidence that these functionals incorporate some desirable aspects of nonlocal exchange. Results for ferromagnetic complexes indicate areas for future improvement.
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75.30.Et Exchange and superexchange interactions

Two- and four-component relativistic generalized-active-space coupled cluster method: Implementation and application to BiH

Lasse K. Sørensen, Jeppe Olsen, and Timo Fleig

J. Chem. Phys. 134, 214102 (2011); http://dx.doi.org/10.1063/1.3592148 (16 pages)

Online Publication Date: 1 June 2011

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A string-based coupled-cluster method of general excitation rank and with optimal scaling which accounts for special relativity within the four-component framework is presented. The method opens the way for the treatment of multi-reference problems through an active-space inspired single-reference based state-selective expansion of the model space. The evaluation of the coupled-cluster vector function is implemented by considering contractions of elementary second-quantized operators without setting up the amplitude equations explicitly. The capabilities of the new method are demonstrated in application to the electronic ground state of the bismuth monohydride molecule. In these calculations simulated multi-reference expansions with both doubles and triples excitations into the external space as well as the regular coupled-cluster hierarchy up to full quadruples excitations are compared. The importance of atomic outer core-correlation for obtaining accurate results is shown. Comparison to the non-relativistic framework is performed throughout to illustrate the additional work of the transition to the four-component relativistic framework both in implementation and application. Furthermore, an evaluation of the highest order scaling for general-order expansions is presented.
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31.15.bw Coupled-cluster theory
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

A smoothly decoupled particle interface: New methods for coupling explicit and implicit solvent

Jason A. Wagoner and Vijay S. Pande

J. Chem. Phys. 134, 214103 (2011); http://dx.doi.org/10.1063/1.3595262 (13 pages)

Online Publication Date: 1 June 2011

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A common theme of studies using molecular simulation is a necessary compromise between computational efficiency and resolution of the forcefield that is used. Significant efforts have been directed at combining multiple levels of granularity within a single simulation in order to maintain the efficiency of coarse-grained models, while using finer resolution in regions where such details are expected to play an important role. A specific example of this paradigm is the development of hybrid solvent models, which explicitly sample the solvent degrees of freedom within a specified domain while utilizing a continuum description elsewhere. Unfortunately, these models are complicated by the presence of structural artifacts at or near the explicit/implicit boundary. The presence of these artifacts significantly complicates the use of such models, both undermining the accuracy obtained and necessitating the parameterization of effective potentials to counteract the artificial interactions. In this work, we introduce a novel hybrid solvent model that employs a smoothly decoupled particle interface (SDPI), a switching region that gradually transitions from fully interacting particles to a continuum solvent. The resulting SDPI model allows for the use of an implicit solvent model based on a simple theory that needs to only reproduce the behavior of bulk solvent rather than the more complex features of local interactions. In this study, the SDPI model is tested on spherical hybrid domains using a coarse-grained representation of water that includes only Lennard-Jones interactions. The results demonstrate that this model is capable of reproducing solvent configurations absent of boundary artifacts, as if they were taken from full explicit simulations.
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33.20.Tp Vibrational analysis
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.xv Molecular dynamics and other numerical methods
31.70.Dk Environmental and solvent effects
33.15.Mt Rotation, vibration, and vibration-rotation constants

Damped response theory description of two-photon absorption

Kasper Kristensen, Joanna Kauczor, Andreas J. Thorvaldsen, Poul Jørgensen, Thomas Kjærgaard, and Antonio Rizzo

J. Chem. Phys. 134, 214104 (2011); http://dx.doi.org/10.1063/1.3595280 (17 pages)

Online Publication Date: 1 June 2011

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Damped response theory is applied to the calculation of two-photon absorption (TPA) spectra, which are determined directly, at each frequency, from a modified damped cubic response function. The TPA spectrum may therefore be evaluated for selected frequency ranges, making the damped TPA approach attractive for calculations on large molecules with a high density of states, where the calculation of TPA using standard theory is more problematic. Damped response theory can also be applied to the case of intermediate state resonances, where the standard TPA expression is divergent. Both exact damped response theory and its application within density functional theory are discussed. The latter is implemented using an atomic-orbital based density matrix formulation, which makes the approach especially suitable for studies on large systems. A test preliminary study is presented for the TPA spectrum of R-(+)-1,1′-bi(2-naphtol).
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.E- Density-functional theory

Approaching the theoretical limit in periodic local MP2 calculations with atomic-orbital basis sets: The case of LiH

Denis Usvyat, Bartolomeo Civalleri, Lorenzo Maschio, Roberto Dovesi, Cesare Pisani, and Martin Schütz

J. Chem. Phys. 134, 214105 (2011); http://dx.doi.org/10.1063/1.3595514 (6 pages) | Cited 1 time

Online Publication Date: 1 June 2011

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The atomic orbital basis set limit is approached in periodic correlated calculations for solid LiH. The valence correlation energy is evaluated at the level of the local periodic second order Møller-Plesset perturbation theory (MP2), using basis sets of progressively increasing size, and also employing “bond”-centered basis functions in addition to the standard atom-centered ones. Extended basis sets, which contain linear dependencies, are processed only at the MP2 stage via a dual basis set scheme. The local approximation (domain) error has been consistently eliminated by expanding the orbital excitation domains. As a final result, it is demonstrated that the complete basis set limit can be reached for both HF and local MP2 periodic calculations, and a general scheme is outlined for the definition of high-quality atomic-orbital basis sets for solids.
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71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

A fluctuating quantum model of the CO vibration in carboxyhemoglobin

Cyril Falvo and Christoph Meier

J. Chem. Phys. 134, 214106 (2011); http://dx.doi.org/10.1063/1.3592707 (11 pages)

Online Publication Date: 1 June 2011

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In this paper, we present a theoretical approach to construct a fluctuating quantum model of the CO vibration in heme-CO proteins and its interaction with external laser fields. The methodology consists of mixed quantum-classical calculations for a restricted number of snapshots, which are then used to construct a parametrized quantum model. As an example, we calculate the infrared absorption spectrum of carboxy-hemoglobin, based on a simplified protein model, and found the absorption linewidth in good agreement with the experimental results.
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87.15.hg Dynamics of intermolecular interactions
87.14.E- Proteins
87.15.ag Quantum calculations
87.15.Ya Fluctuations
36.20.Ng Vibrational and rotational structure, infrared and Raman spectra
36.20.Kd Electronic structure and spectra

Two-component natural spinors from two-step spin-orbit coupled wave functions

Tao Zeng, Dmitri G. Fedorov, Michael W. Schmidt, and Mariusz Klobukowski

J. Chem. Phys. 134, 214107 (2011); http://dx.doi.org/10.1063/1.3592780 (9 pages)

Online Publication Date: 1 June 2011

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We developed an algorithm to obtain the natural orbitals (natural spinors) from the two-step spin-orbit coupled wave functions. These natural spinors are generally complex-valued, mixing two spin components, and they can have similar symmetry properties as the j-j spinors from the one-step spin-orbit coupling calculations, if the reduced density equally averages all the components of a multi-dimensional irreducible representation. Therefore, the natural spinors can serve as an approximation to the j-j spinors and any wave function analysis based on the j-j spinors can also be performed based on them. The comparison between the natural spinors and the j-j spinors of three representative atoms, Tl, At, and Lu, shows their close similarity and demonstrates the ability of the natural spinors to approximate the j-j spinors.
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31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Correcting model energies by numerically integrating along an adiabatic connection and a link to density functional approximations

Andreas Savin

J. Chem. Phys. 134, 214108 (2011); http://dx.doi.org/10.1063/1.3592782 (10 pages)

Online Publication Date: 1 June 2011

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Model Hamiltonians are considered for which electrons interact via long-range forces. It is assumed that their eigenvalues can be obtained with satisfying accuracy. Extrapolation techniques using asymptotic behavior considerations provide estimates for the energy of the physical system. Results for the uniform electron gas and some two-electron systems show that very few quadrature points can already produce good quality results. Connections to the density functional theory are discussed.
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31.15.E- Density-functional theory

A novel interpretation of reduced density matrix and cumulant for electronic structure theories

Liguo Kong and Edward F. Valeev

J. Chem. Phys. 134, 214109 (2011); http://dx.doi.org/10.1063/1.3596948 (9 pages) | Cited 1 time

Online Publication Date: 2 June 2011

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We propose a novel interpretation of the reduced density matrix (RDM) and its cumulant that combines linear and exponential parametrizations of the wavefunction. Any n-particle RDM can be written as a weighted average of “configuration interaction” amplitudes. The corresponding n-particle cumulant is represented in terms of two types of contributions: “connected” (statistical averages of substitution amplitudes) and “disconnected” (cross-correlations of substitution amplitudes). A diagonal element of n-RDM represents the average occupation number of the orbital n-tuple. The diagonal elements of 2- and 3-cumulants take particularly elegant forms in the natural spin-orbital basis: they represent the covariances (correlated fluctuations) of the occupation numbers of the orbital pair and triples, respectively. Thus, the diagonal elements of the cumulants quantify the correlation between the orbital occupation numbers. Our interpretation is used to examine the weak to strong correlation transition in the “two electrons in two orbitals” problem.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
02.10.Yn Matrix theory

Development of a new variational approach for thermal density matrices

Tapta Kanchan Roy and M. Durga Prasad

J. Chem. Phys. 134, 214110 (2011); http://dx.doi.org/10.1063/1.3592777 (8 pages)

Online Publication Date: 2 June 2011

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A McLachlan-type variational principle is derived for thermal density matrices. In this approach, the trace of the mean square of the differences between the derivatives of the exact and model density matrices is minimized with respect to the parameters in the model Hamiltonian. Applications to model anharmonic systems in the independent particle model show that the method can provide thermodynamic state functions accurately (within 5% of the converged basis set results) and at the same level of accuracy as the results using Feynman-Gibbs-Bogoliubov variational principle at this level of approximation.
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31.15.xt Variational techniques

Transferable model of water with variable molecular size

Péter T. Kiss and András Baranyai

J. Chem. Phys. 134, 214111 (2011); http://dx.doi.org/10.1063/1.3596727 (6 pages)

Online Publication Date: 3 June 2011

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By decreasing the steepness of the repulsive wing in the intermolecular potential, one can extend the applicability of a water model to the high pressure region. Exploiting this trivial possibility, we published a polarizable model of water which provided good estimations not only of gas clusters, ambient liquid, hexagonal ice, but ice VII at very high pressures as well [A. Baranyai and P. Kiss, J. Chem. Phys. 133, 144109 (2010)10.1063/1.3490660]. This straightforward method works well provided the closest O–O distance is reasonably shorter in the high pressure phase than in hexagonal ice. If these O–O distances are close to each other and we fit the interactions to obtain an accurate picture of hexagonal ice, we underestimate the density of the high-pressure phases. This can be overcome if models use contracted molecules under high external pressure.In this paper we present a method, which is capable to describe the contraction of water molecules under high pressure by using two simple repulsion-attraction functions. These functions represent the dispersion interaction under low pressure and high pressure. The switch function varies between 0 and 1 and portions the two repulsions among the individual particles. The argument of the switch function is a virial-type expression, which can be interpreted as a net force compressing the molecule. We calculated the properties of gas clusters, densities, and internal energies of ambient water, hexagonal ice, ice III, ice VI, and ice VII phases and obtained excellent match of experimental data.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
36.40.-c Atomic and molecular clusters
33.15.Dj Interatomic distances and angles

Entropy production in a mesoscopic chemical reaction system with oscillatory and excitable dynamics

Ting Rao, Tiejun Xiao, and Zhonghuai Hou

J. Chem. Phys. 134, 214112 (2011); http://dx.doi.org/10.1063/1.3598111 (7 pages)

Online Publication Date: 7 June 2011

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Stochastic thermodynamics of chemical reaction systems has recently gained much attention. In the present paper, we consider such an issue for a system with both oscillatory and excitable dynamics, using catalytic oxidation of carbon monoxide on the surface of platinum crystal as an example. Starting from the chemical Langevin equations, we are able to calculate the stochastic entropy production P along a random trajectory in the concentration state space. Particular attention is paid to the dependence of the time-averaged entropy production P on the system size N in a parameter region close to the deterministic Hopf bifurcation (HB). In the large system size (weak noise) limit, we find that P ∼ Nβ with β = 0 or 1, when the system is below or above the HB, respectively. In the small system size (strong noise) limit, P always increases linearly with N regardless of the bifurcation parameter. More interestingly, P could even reach a maximum for some intermediate system size in a parameter region where the corresponding deterministic system shows steady state or small amplitude oscillation. The maximum value of P decreases as the system parameter approaches the so-called CANARD point where the maximum disappears. This phenomenon could be qualitatively understood by partitioning the total entropy production into the contributions of spikes and of small amplitude oscillations.
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82.20.-w Chemical kinetics and dynamics
82.40.Bj Oscillations, chaos, and bifurcations
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Extended multi-configuration quasi-degenerate perturbation theory: The new approach to multi-state multi-reference perturbation theory

Alexander A. Granovsky

J. Chem. Phys. 134, 214113 (2011); http://dx.doi.org/10.1063/1.3596699 (14 pages) | Cited 1 time

Online Publication Date: 7 June 2011

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The distinctive desirable features, both mathematically and physically meaningful, for all partially contracted multi-state multi-reference perturbation theories (MS-MR-PT) are explicitly formulated. The original approach to MS-MR-PT theory, called extended multi-configuration quasi-degenerate perturbation theory (XMCQDPT), having most, if not all, of the desirable properties is introduced. The new method is applied at the second order of perturbation theory (XMCQDPT2) to the 11A′ – 21A′ conical intersection in allene molecule, the avoided crossing in LiF molecule, and the 11A1 to 21A1 electronic transition in cis-1,3-butadiene. The new theory has several advantages compared to those of well-established approaches, such as second order multi-configuration quasi-degenerate perturbation theory and multi-state-second order complete active space perturbation theory. The analysis of the prevalent approaches to the MS-MR-PT theory performed within the framework of the XMCQDPT theory unveils the origin of their common inherent problems. We describe the efficient implementation strategy that makes XMCQDPT2 an especially useful general-purpose tool in the high-level modeling of small to large molecular systems.
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31.15.xp Perturbation theory
33.80.Be Level crossing and optical pumping
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Reduction of the virtual space for coupled-cluster excitation energies of large molecules and embedded systems

Robert Send, Ville R. I. Kaila, and Dage Sundholm

J. Chem. Phys. 134, 214114 (2011); http://dx.doi.org/10.1063/1.3596729 (9 pages)

Online Publication Date: 7 June 2011

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We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50  eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1  eV . By using a RVS energy threshold of 50  eV , the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2/TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics/molecular mechanics separation schemes.
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31.15.bw Coupled-cluster theory
87.14.E- Proteins
36.20.-r Macromolecules and polymer molecules

A graph-theoretical kinetic Monte Carlo framework for on-lattice chemical kinetics

Michail Stamatakis and Dionisios G. Vlachos

J. Chem. Phys. 134, 214115 (2011); http://dx.doi.org/10.1063/1.3596751 (13 pages) | Cited 1 time

Online Publication Date: 7 June 2011

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Existing kinetic Monte Carlo (KMC) frameworks for the simulation of adsorption, desorption, diffusion, and reaction on a lattice often assume that each participating species occupies a single site and represent elementary events involving a maximum of two sites. However, these assumptions may be inadequate, especially in the case of complex chemistries, involving multidentate species or complex coverage and neighboring patterns between several lattice sites. We have developed a novel approach that employs graph-theoretical ideas to overcome these challenges and treat easily complex chemistries. As a benchmark, the Ziff-Gulari-Barshad system is simulated and comparisons of the computational times of the graph-theoretical KMC and a simpler KMC approach are made. Further, to demonstrate the capabilities of our framework, the water-gas shift chemistry on Pt(111) is simulated.
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82.20.Db Transition state theory and statistical theories of rate constants
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Nr Desorption kinetics
02.10.Ox Combinatorics; graph theory
02.50.Ng Distribution theory and Monte Carlo studies
68.43.Mn Adsorption kinetics

A state-specific partially internally contracted multireference coupled cluster approach

Dipayan Datta, Liguo Kong, and Marcel Nooijen

J. Chem. Phys. 134, 214116 (2011); http://dx.doi.org/10.1063/1.3592494 (19 pages) | Cited 2 times

Online Publication Date: 7 June 2011

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A state-specific partially internally contracted multireference coupled cluster approach is presented for general complete active spaces with arbitrary number of active electrons. The dominant dynamical correlation is included via an exponential parametrization of internally contracted cluster operators (math) which excite electrons from a multideterminantal reference function. The remaining dynamical correlation and relaxation effects are included via a diagonalization of the transformed Hamiltonian math = mathmathmath in the multireference configuration interaction singles space in an uncontracted fashion. A new set of residual equations for determining the internally contracted cluster amplitudes is proposed. The second quantized matrix elements of math, expressed using the extended normal ordering of Kutzelnigg and Mukherjee, are used as the residual equations without projection onto the excited configurations. These residual equations, referred to as the many-body residuals, do not have any near-singularity and thus, should allow one to solve all the amplitudes without discarding any. There are some relatively minor remaining convergence issues that may arise from an attempt to solve all the amplitudes and an initial analysis is provided in this paper. Applications to the bond-stretching potential energy surfaces for N2, CO, and the low-lying electronic states of C2 indicate clear improvements of the results using the many-body residuals over the conventional projected residual equations.
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31.15.bw Coupled-cluster theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.vn Electron correlation calculations for diatomic molecules
31.50.Df Potential energy surfaces for excited electronic states
33.15.Fm Bond strengths, dissociation energies

Phonostat: Thermostatting phonons in molecular dynamics simulations

Rajamani Raghunathan, P. Alex Greaney, and Jeffrey C. Grossman

J. Chem. Phys. 134, 214117 (2011); http://dx.doi.org/10.1063/1.3597605 (9 pages)

Online Publication Date: 7 June 2011

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Thermostat algorithms in a molecular dynamics simulation maintain an average temperature of a system by regulating the atomic velocities rather than the internal degrees of freedom. Herein, we present a “phonostat” algorithm that can regulate the total energy in a given internal degree of freedom. In this algorithm, the modal energies are computed at each time step using a mode-tracking scheme and then the system is driven by an external driving force of desired frequency and amplitude. The rate and amount of energy exchange between the phonostat and the system is controlled by two distinct damping parameters. Two different schemes for controlling the external driving force amplitude are also presented. In order to test our algorithm, the method is applied initially to a simple anharmonic oscillator for which the role of various phonostat parameters can be carefully tested. We then apply the phonostat to a more realistic (10,0) carbon nanotube system and show how such an approach can be used to regulate energy of highly anharmonic modes.
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63.20.Ry Anharmonic lattice modes
61.43.Bn Structural modeling: serial-addition models, computer simulation
63.10.+a General theory
63.22.Gh Nanotubes and nanowires

Multi-reference state-universal coupled-cluster approaches to electronically excited states

Xiangzhu Li and Josef Paldus

J. Chem. Phys. 134, 214118 (2011); http://dx.doi.org/10.1063/1.3595513 (15 pages) | Cited 2 times

Online Publication Date: 7 June 2011

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The multi-reference (MR), general model space (GMS), state-universal (SU), coupled-cluster (CC) method with singles and doubles (GMS-SU-CCSD), as well as its triple-corrected versions GMS-SU-CCSD(T), are employed to assess their ability to describe low-lying excited states of various molecules, with an emphasis on a simultaneous handling of several states of the same symmetry species. A special attention is given to the role of the so-called C-conditions that account for non-vanishing internal cluster amplitudes when relying on an incomplete GMS, as well as to the choice of suitable model spaces and a perturbative account of secondary triples. The ambiguities arising when using large basis sets are also pointed out. To achieve a general assessment of the potential of the GMS-type SU-CC approaches, the vertical excitation energies of several species, including the challenging BN diatomic as well as larger systems, namely formaldehyde, trans-butadiene, formamide, and benzene are considered. These results are compared with those provided by the equation-of-motion EOM-CCSD method and, whenever available, the density functional theory results and experimental data. These comparisons clearly demonstrate the usefulness of GMS-type MR-CC approaches.
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31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

I−·(CH3I)2 photoexcitation: The influence of dipole bound states on detachment and fragmentation

Matthew Van Duzor, Foster Mbaiwa, Joshua Lasinski, Nicholas Holtgrewe, and Richard Mabbs

J. Chem. Phys. 134, 214301 (2011); http://dx.doi.org/10.1063/1.3594177 (7 pages)

Online Publication Date: 1 June 2011

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We present the results of a photoelectron imaging study of the I−·(CH3I)2 cluster anion over excitation wavelengths 355–260 nm. The resulting spectra and photoelectron angular distributions (PADs) suggest extensive electron-molecule interaction following photoexcitation. Fragmentation channels are observed subsequent to excitation between 355 and 330 nm. The origin of these features, which begin 200 meV and peak 70 meV below the X band direct detachment threshold, is described in terms of a predissociative dipole bound state. The nature of the fragments detected and the energetics of the channel opening argue strongly in favor of an asymmetric, head to tail cluster anion geometry posited by Dessent et al. [Acc. Chem. Res. 31, 527 (1998)]10.1021/ar950061f. Above the direct detachment threshold, PADs display evidence of phenomena akin to electron-molecule scattering. The fragment anions disappear above the X band threshold but reappear some distance below the second (A) direct detachment band. At these energies there is also rapid variation of the X band PAD, an observation attributed to autodetachment via spin-orbit relaxation of the iodine core of the cluster.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
34.80.Bm Elastic scattering
34.80.Gs Molecular excitation and ionization
36.40.Jn Reactivity of clusters
36.40.Wa Charged clusters

Rotationally resolved infrared spectrum of the Na+-D2 complex: An experimental and theoretical study

B. L. J. Poad, V. Dryza, J. Kłos, A. A. Buchachenko, and E. J. Bieske

J. Chem. Phys. 134, 214302 (2011); http://dx.doi.org/10.1063/1.3596720 (6 pages)

Online Publication Date: 2 June 2011

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The infrared spectrum of mass-selected Na+-D2 complexes is recorded in the D-D stretch vibration region (2915-2972 cm−1) by detecting Na+ photofragments resulting from photo-excitation of the complexes. Analysis of the rotationally resolved spectrum confirms a T-shaped equilibrium geometry for the complex and a vibrationally averaged intermolecular bond length of 2.461 Å. The D-D stretch band centre occurs at 2944.04 cm−1, representing a −49.6 cm−1 shift from the Q1(0) transition of the free D2 molecule. Variational rovibrational energy level calculations are performed for Na+-D2 utilising an ab initio potential energy surface developed previously for investigating the Na+-H2 complex [B. L. J. Poad et al., J. Chem. Phys. 129, 184306 (2008)]10.1063/1.3005785. The theoretical approach predicts a dissociation energy for Na+-D2 of 923 cm−1 with respect to the Na++ D2 limit, reproduces the experimental rotational constants to within 1-2%, and gives a simulated spectrum closely matching the experimental infrared spectrum.
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33.20.Ea Infrared spectra
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants

Quantum dynamics of rovibrational transitions in H2-H2 collisions: Internal energy and rotational angular momentum conservation effects

S. Fonseca dos Santos, N. Balakrishnan, S. Lepp, G. Quéméner, R. C. Forrey, R. J. Hinde, and P. C. Stancil

J. Chem. Phys. 134, 214303 (2011); http://dx.doi.org/10.1063/1.3595134 (11 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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We present a full dimensional quantum mechanical treatment of collisions between two H2 molecules over a wide range of energies. Elastic and state-to-state inelastic cross sections for ortho-H2 + para-H2 and ortho-H2 + ortho-H2 collisions have been computed for different initial rovibrational levels of the molecules. For rovibrationally excited molecules, it has been found that state-to-state transitions are highly specific. Inelastic collisions that conserve the total rotational angular momentum of the diatoms and that involve small changes in the internal energy are found to be highly efficient. The effectiveness of these quasiresonant processes increases with decreasing collision energy and they become highly state-selective at ultracold temperatures. They are found to be more dominant for rotational energy exchange than for vibrational transitions. For non-reactive collisions between ortho- and para-H2 molecules for which rotational energy exchange is forbidden, the quasiresonant mechanism involves a purely vibrational energy transfer albeit with less efficiency. When inelastic collisions are dominated by a quasiresonant transition calculations using a reduced basis set involving only the quasiresonant channels yield nearly identical results as the full basis set calculation leading to dramatic savings in computational cost.
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34.50.Ez Rotational and vibrational energy transfer

Ab initio characterization of the Ne–I2 van der Waals complex: Intermolecular potentials and vibrational bound states

Laura Delgado-Tellez, Álvaro Valdés, Rita Prosmiti, Pablo Villarreal, and Gerardo Delgado-Barrio

J. Chem. Phys. 134, 214304 (2011); http://dx.doi.org/10.1063/1.3596604 (9 pages) | Cited 2 times

Online Publication Date: 6 June 2011

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A theoretical study of the potential energy surface and bound states is performed for the ground state of the NeI2 van der Waals (vdW) complex. The three-dimensional interaction energies are obtained from ab initio coupled-cluster, coupled-cluster single double (triple)/complete basis set, calculations using large basis sets, of quadruple- through quintuple-zeta quality, in conjunction with relativistic effective core potentials for the heavy iodine atoms. For the analytical representation of the surface two different schemes, based on fitting and interpolation surface generation techniques, are employed. The surface shows a double-minimum topology for linear and T-shaped configurations. Full variational quantum mechanical calculations are carried out using the model surfaces, and the vibrationally averaged structures and energetics for the NeI2 isomers are determined. The accuracy of the potential energy surfaces is validated by a comparison between the present results and the corresponding experimental data available. In lieu of more experimental measurements, we also report our results/predictions on higher bound vibrational vdW levels, and the influence of the employed surface on them is discussed.
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31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
34.20.Gj Intermolecular and atom-molecule potentials and forces

Measuring polarizability anisotropies of rare gas diatomic molecules by laser-induced molecular alignment technique

Shinichirou Minemoto and Hirofumi Sakai

J. Chem. Phys. 134, 214305 (2011); http://dx.doi.org/10.1063/1.3594681 (9 pages)

Online Publication Date: 6 June 2011

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The polarizability anisotropies of homonuclear rare gas diatomic molecules, Ar2, Kr2, and Xe2, are investigated by utilizing the interaction of the induced electric dipole moment with a nonresonant, nanosecond laser pulse. The degree of alignment, which depends on the depth of the interaction potential created by the intense laser field, is measured, and is found to increase in order of Ar2, Kr2, and Xe2 at the same peak intensity. Compared with a reference I2 molecule, Ar2, Kr2, and Xe2 are found to have the polarizability anisotropies of 0.45 ± 0.13, 0.72 ± 0.13, and 1.23 ± 0.21 Å3, respectively, where the uncertainties (one standard deviation) in the polarizability anisotropies are carefully evaluated on the basis of the laser intensity dependence of the degree of alignment. The obtained values are compared with recent theoretical calculations and are found to agree well within the experimental uncertainties.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.80.Wz Other multiphoton processes
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation
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Nanoconfinement effects on the reversibility of hydrogen storage in ammonia borane: A first-principles study

Kiseok Chang, Eunja Kim, Philippe F. Weck, and David Tománek

J. Chem. Phys. 134, 214501 (2011); http://dx.doi.org/10.1063/1.3594115 (7 pages)

Online Publication Date: 1 June 2011

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We investigate atomistic mechanisms governing hydrogen release and uptake processes in ammonia borane (AB) within the framework of the density functional theory. In order to determine the most favorable pathways for the thermal inter-conversion between AB and polyaminoborane plus H2, we calculate potential energy surfaces for the corresponding reactions. We explore the possibility of enclosing AB in narrow carbon nanotubes to limit the formation of undesirable side-products such as the cyclic compound borazine, which hinder subsequent rehydrogenation of the system. We also explore the effects of nanoconfinement on the possible rehydrogenation pathways of AB and suggest the use of photoexcitation as a means to achieve dehydrogenation of AB at low temperatures.
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88.30.rd Inorganic metal hydrides
82.20.Kh Potential energy surfaces for chemical reactions
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