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1 Mar 2005

Volume 122, Issue 9, Articles (09xxxx)

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Continuous configuration time-dependent self-consistent field method for polyatomic quantum dynamical problems

Dong H. Zhang, Weizhu Bao, Minghui Yang, and Soo-Y. Lee

J. Chem. Phys. 122, 091101 (2005); http://dx.doi.org/10.1063/1.1869496 (4 pages) | Cited 3 times

Online Publication Date: 25 February 2005

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A new continuous configuration time-dependent self-consistent field method has been developed to study polyatomic dynamical problems by using the discrete variable representation for the reaction system, and applied to a reaction system coupled to a bath. The method is very efficient because the equations involved are as simple as those in the traditional single configuration approach, and can account for the correlations between the reaction system and bath modes rather well.
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82.20.-w Chemical kinetics and dynamics

Accelerating quantum mechanical/molecular mechanical sampling using pure molecular mechanical potential as an importance function: The case of effective fragment potential

Pradipta Bandyopadhyay

J. Chem. Phys. 122, 091102 (2005); http://dx.doi.org/10.1063/1.1861890 (4 pages) | Cited 14 times

Online Publication Date: 25 February 2005

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Acceleration of sampling from a quantum mechanical/effective fragment mechanical (QM/EFP) potential is explored with effective fragment potential (EFP) as an importance function. EFP, generated on the fly, is found to be an excellent choice for an importance function for a QM/EFP potential. This technique is used to find nine stationary points of a blocked amino acid with twelve waters in a semi-automated way.
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31.15.xv Molecular dynamics and other numerical methods
34.20.Gj Intermolecular and atom-molecule potentials and forces

The stabilization of arginine’s zwitterion by dipole-binding of an excess electron

Shoujun Xu, Weijun Zheng, Dunja Radisic, and Kit H. Bowen

J. Chem. Phys. 122, 091103 (2005); http://dx.doi.org/10.1063/1.1864952 (3 pages) | Cited 11 times

Online Publication Date: 2 March 2005

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The arginine parent anion was generated by a newly developed, infrared desorption-electron photoemission hybrid anion source. The photoelectron spectrum of the arginine anion was recorded and interpreted as being due to dipole binding of the excess electron. The results are consistent with calculations by Rak, Skurski, Simons, and Gutowski, who predicted the near degeneracy of arginine’s canonical and zwitterionic dipole bound anions. Since neutral arginine’s zwitterion is slightly less stable than its canonical form, this work also demonstrates the ability of an excess electron to stabilize a zwitterion, just as ions and solvent molecules are already known to do.
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87.15.M- Spectra of biomolecules
33.60.+q Photoelectron spectra
34.80.Lx Recombination, attachment, and positronium formation
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Novel method for selective probing of ground-state rotational dynamics of solutes in solvents

Thai V. Truong and Y. R. Shen

J. Chem. Phys. 122, 091104 (2005); http://dx.doi.org/10.1063/1.1864953 (4 pages) | Cited 3 times

Online Publication Date: 2 March 2005

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We introduce an optical pump/probe method that allows selective measurement of ground-state rotational dynamics of solutes in liquids. It relies on employing two successive pump pulses that are adjusted to create an optical anisotropy due to the orientational distribution of only the ground-state solute molecules. Measurement on a dye-solvent system shows a large difference between the rotational diffusion rates of the ground state and the excited state of the dye molecules due to different solute–solvent interactions.
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66.10.C- Diffusion and thermal diffusion
78.20.Fm Birefringence
61.25.Em Molecular liquids

Isomer selective infrared spectroscopy of neutral metal clusters

André Fielicke, Christian Ratsch, Gert von Helden, and Gerard Meijer

J. Chem. Phys. 122, 091105 (2005); http://dx.doi.org/10.1063/1.1872834 (4 pages) | Cited 25 times

Online Publication Date: 4 March 2005

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We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80–400 cm−1 region. The observed spectra for Nb9Arn (n = 1–4) are different for different values of n. This is explained by the presence of two isomers of Nb9 that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.
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36.40.Mr Spectroscopy and geometrical structure of clusters
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back to top Theoretical Methods and Algorithms

Molecular wave packet interferometry and quantum entanglement

Ricardo Martínez-Galicia and Víctor Romero-Rochín

J. Chem. Phys. 122, 094101 (2005); http://dx.doi.org/10.1063/1.1852456 (11 pages) | Cited 3 times

Online Publication Date: 24 February 2005

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We study wave packet interferometry (WPI) considering the laser pulse fields both classical and quantum mechanically. WPI occurs in a molecule after subjecting it to the interaction with a sequence of phase-locked ultrashort laser pulses. Typically, the measured quantity is the fluorescence of the molecule from an excited electronic state. This signal has imprinted the interference of the vibrational wave packets prepared by the different laser pulses of the sequence. The consideration of the pulses as quantum entities in the analysis allows us to study the entanglement of the laser pulse states with the molecular states. With a simple model for the molecular system, plus several justified approximations, we solve for the fully quantum mechanical molecule-electromagnetic field state. We then study the reduced density matrices of the molecule and the laser pulses separately. We calculate measurable corrections to the case where the fields are treated classically.
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33.80.-b Photon interactions with molecules
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
31.50.Df Potential energy surfaces for excited electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra

Mixed quantum-classical equilibrium

Priya V. Parandekar and John C. Tully

J. Chem. Phys. 122, 094102 (2005); http://dx.doi.org/10.1063/1.1856460 (6 pages) | Cited 48 times

Online Publication Date: 24 February 2005

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We present an analysis of the equilibrium limits of the two most widely used approaches for simulating the dynamics of molecular systems that combine both quantum and classical degrees of freedom. For a two-level quantum system connected to an infinite number of classical particles, we derive a simple analytical expression for the equilibrium mean energy attained by the self-consistent-field (Ehrenfest) method and show that it deviates substantially from Boltzmann. By contrast, “fewest switches” surface hopping achieves Boltzmann quantum state populations. We verify these analytical results with simulations.
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31.15.xr Self-consistent-field methods

Dynamics of coupled Bohmian and phase-space variables: A moment approach to mixed quantum-classical dynamics

Irene Burghardt

J. Chem. Phys. 122, 094103 (2005); http://dx.doi.org/10.1063/1.1856462 (11 pages) | Cited 12 times

Online Publication Date: 24 February 2005

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The theoretical framework of the mixed quantum-classical description given by Burghardt and Parlant [ J. Chem. Phys. 120, 3055 (2004) ] is detailed. A representation in terms of partial hydrodynamic moments is developed, the dynamics of which is determined by a hierarchy of equations derived from the quantum Liouville equation. Exact equations of motion are obtained, whose quantum-classical approximants are associated with a fluid-dynamical trajectory representation which couples classical variables to quantum hydrodynamic variables. The latter evolve under a generalized hydrodynamic force which also depends upon the classical phase-space variables. The hydrodynamic moment description is shown to be closely connected to mixed quantum-classical phase-space methods.
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47.10.-g General theory in fluid dynamics
02.30.Rz Integral equations
02.60.Nm Integral and integrodifferential equations
45.05.+x General theory of classical mechanics of discrete systems
03.65.Fd Algebraic methods

Numerical study of the accuracy and efficiency of various approaches for Monte Carlo surface hopping calculations

Michael F. Herman and Michael P. Moody

J. Chem. Phys. 122, 094104 (2005); http://dx.doi.org/10.1063/1.1855313 (9 pages) | Cited 13 times

Online Publication Date: 25 February 2005

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A one-dimensional, two-state model problem with two well-separated avoided crossing points is employed to test the efficiency and accuracy of a semiclassical surface hopping technique. The use of a one-dimensional model allows for the accurate numerical evaluation of both fully quantum-mechanical and semiclassical transition probabilities. The calculations demonstrate that the surface hopping procedure employed accounts for the interference between different hopping trajectories very well and provides highly accurate transition probabilities. It is, in general, not computationally feasible to completely sum over all hopping trajectories in the semiclassical calculations for multidimensional problems. In this case, a Monte Carlo procedure for selecting important trajectories can be employed. However, the cancellation due to the different phases associated with different trajectories limits the accuracy and efficiency of the Monte Carlo procedure. Various approaches for improving the accuracy and efficiency of Monte Carlo surface hopping procedures are investigated. These methods are found to significantly reduce the statistical sampling errors in the calculations, thereby increasing the accuracy of the transition probabilities obtained with a fixed number of trajectories sampled.
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03.65.Sq Semiclassical theories and applications
02.50.Ng Distribution theory and Monte Carlo studies

Third- and fourth-order perturbation corrections to excitation energies from configuration interaction singles

So Hirata

J. Chem. Phys. 122, 094105 (2005); http://dx.doi.org/10.1063/1.1855883 (10 pages) | Cited 19 times

Online Publication Date: 25 February 2005

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Complete third-order and partial fourth-order Rayleigh–Schrödinger perturbation corrections to excitation energies from configuration interaction singles (CIS) have been derived and termed CIS(3) and CIS(4)P. They have been implemented by the automated system TENSOR CONTRACTION ENGINE into parallel-execution programs taking advantage of spin, spatial, and index permutation symmetries and applicable to closed- and open-shell molecules. The consistent use of factorization, first introduced by Head-Gordon et al. in the second-order correction to CIS denoted CIS(D), has reduced the computational cost of CIS(3) and CIS(4)P from O(n8) and O(n6) to O(n6) and O(n5), respectively, with n being the number of orbitals. It has also guaranteed the size extensivity of excited-state energies of these methods, which are in turn the sum of size-intensive excitation energies and the ground-state energies from the standard Møller–Plesset perturbation theory at the respective orders. The series CIS(D), CIS(3), and CIS(4)P are usually monotonically convergent at values close to the accurate results predicted by coupled-cluster singles and doubles (CCSD) with a small fraction of computational costs of CCSD for predominantly singly excited states characterized by a 90%–100% overlap between the CIS and CCSD wave functions. When the overlap is smaller, the perturbation theory is incapable of adequately accounting for the mixing of the CIS states through higher-than-singles sectors of the Hamiltonian matrix, resulting in wildly oscillating series with often very large errors in CIS(4)P. Hence, CIS(3) and CIS(4)P have a rather small radius of convergence and a limited range of applicability, but within that range they can be an inexpensive alternative to CCSD.
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31.15.xp Perturbation theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.bw Coupled-cluster theory

Role of angular momentum conservation in unimolecular translational energy release: Validity of the orbiting transition state theory

E. Gridelet, J. C. Lorquet, and B. Leyh

J. Chem. Phys. 122, 094106 (2005); http://dx.doi.org/10.1063/1.1856917 (14 pages) | Cited 6 times

Online Publication Date: 28 February 2005

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The translational kinetic energy release distribution (KERD) for the halogen loss reaction of the bromobenzene and iodobenzene cations has been reinvestigated on the microsecond time scale. Two necessary conditions of validity of the orbiting transition state theory (OTST) for the calculation of kinetic energy release distributions (KERDs) have been formulated. One of them examines the central ion-induced dipole potential approximation. As a second criterion, an adiabatic parameter is derived. The lower the released translational energy and the total angular momentum, the larger the reduced mass, the rotational constant of the molecular fragment, and the polarizability of the released atom, the more valid is the OTST. Only the low-energy dissociation of the iodobenzene ion (E ≈ 0.45 eV, where E is the internal energy above the reaction threshold) is found to fulfill the criteria of validity of the OTST. The constraints that act on the dissociation dynamics have been studied by the maximum entropy method. Calculations of entropy deficiencies (which measure the deviation from a microcanonical distribution) show that the pair of fragments does not sample the whole of the phase space that is compatible with the mere specification of the internal energy. The major constraint that results from conservation of angular momentum is related to a reduction of the dimensionality of the dynamics of the translational motion to a two-dimensional space. A second and minor constraint that affects the KERD leads to a suppression of small translational releases, i.e., accounts for threshold behavior. At high internal energies, the effects of curvature of the reaction path and of angular momentum conservation are intricately intermeddled and it is not possible to specify the share of each effect.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Fd Collision theories; trajectory models
82.20.Pm Rate constants, reaction cross sections, and activation energies

Application of variational reduced-density-matrix theory to organic molecules

Gergely Gidofalvi and David A. Mazziotti

J. Chem. Phys. 122, 094107 (2005); http://dx.doi.org/10.1063/1.1855885 (8 pages) | Cited 23 times

Online Publication Date: 28 February 2005

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Variational calculation of the two-electron reduced-density matrix (2-RDM), using a new first-order algorithm [ D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004) ], is applied to medium-sized organic molecules. The calculations reveal systematic trends in the accuracy of the energy with well-known chemical concepts such as hybridization, electronegativity, and atomic size. Furthermore, correlation energies from hydrocarbon chains indicate that the calculation of the 2-RDM subject to two-positivity conditions is size extensive, that is, the energy grows linearly with the number of electrons. Because organic molecules have a well-defined set of functional groups, we employ the trends in energy accuracy of the functional groups to design a correction to the 2-RDM energy for an arbitrary organic molecule. We apply the 2-RDM calculations with the functional-group correction to a large set of organic molecules with different functional groups. Energies with millihartree accuracy are obtained both at equilibrium and nonequilibrium geometries.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.xt Variational techniques
02.10.Yn Matrix theory

Stationary phase evaluations of quantum rate constants

Shilong Yang and Jianshu Cao

J. Chem. Phys. 122, 094108 (2005); http://dx.doi.org/10.1063/1.1856461 (10 pages) | Cited 5 times

Online Publication Date: 1 March 2005

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We compute the quantum rate constant based on two extended stationary phase approximations to the imaginary-time formulation of the quantum rate theory. The optimized stationary phase approximation to the imaginary-time flux-flux correlation function employs the optimized quadratic reference system to overcome the inaccuracy of the quadratic expansion in the standard stationary phase approximation, and yields favorable agreements with instanton results for both adiabatic and nonadiabatic processes in dissipative and nondissipative systems. The integrated stationary phase approximation to the two-dimensional barrier free energy is particularly useful for adiabatic processes and demonstrates consistent results with the imaginary-time flux-flux correlation function approach. Our stationary phase methods do not require calculation of tunneling paths or stability matrices, and work equally well in the high-temperature and the low-temperature regimes. The numerical results suggest their general applicability for calibration of imaginary-time methods and for the calculation of quantum rate constants in systems with a large number of degrees of freedom.
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82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.20.Sb Correlation function theory of rate constants and its applications
02.10.Yn Matrix theory

Testing wave packet dynamics in computing radiative association cross sections

Rocco Martinazzo and Gian Franco Tantardini

J. Chem. Phys. 122, 094109 (2005); http://dx.doi.org/10.1063/1.1857476 (9 pages) | Cited 1 time

Online Publication Date: 1 March 2005

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A time-dependent wave packet method is used to compute cross sections for radiative recombination reactions using the Li(math)+H+→LiH+(X math)+γ as a test case. Cross sections are calculated through standard time-to-energy mapping of the time-dependent transition moment and a useful method is introduced to deal with the low collision energy regime. Results are in quantitative agreement over the whole energy range 10−4–5 eV with previous time-independent results for the same system [ I. Baccarelli, L. Andric, T. Grozdanov, and R. McCarroll, J. Chem. Phys. 117, 3013 (2002)] , thereby suggesting that the method can be of help in computing radiative association cross sections for more complicated systems.
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82.30.Nr Association, addition, insertion, cluster formation
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Wt Computational modeling; simulation

Electron correlation in Hooke’s law atom in the high-density limit

P. M. W. Gill and D. P. O’Neill

J. Chem. Phys. 122, 094110 (2005); http://dx.doi.org/10.1063/1.1862237 (4 pages) | Cited 19 times

Online Publication Date: 1 March 2005

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Closed-form expressions for the first three terms in the perturbation expansion of the exact energy and Hartree–Fock energy of the lowest singlet and triplet states of the Hooke’s law atom are found. These yield elementary formulas for the exact correlation energies (−49.7028 and −5.807 65 mEh) of the two states in the high-density limit and lead to a pair of necessary conditions on the exact correlation kernel G(w) in Hartree–Fock–Wigner theory.
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31.15.vj Electron correlation calculations for atoms and ions: excited states

Multireference configuration interaction based electronic Floquet states for molecules in an intense radiation field: Theory and application to Li2+

Yuriy G. Khait, Alexander Azenkeng, Hefeng Wang, Timothy J. Dudley, and Mark R. Hoffmann

J. Chem. Phys. 122, 094111 (2005); http://dx.doi.org/10.1063/1.1856452 (10 pages) | Cited 5 times

Online Publication Date: 1 March 2005

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A multireference configuration interaction (CI) method which includes single and double excitations based description of adiabatic Floquet states for the electronic structure of a molecule in an intense laser field is introduced. Using a variant of a recently introduced configuration state function (CSF) based Table-CI methodology, it is shown that the multiple states of several irreducible representations required for a good description of low-lying Floquet states can be obtained using modifications of computational molecular electronic structure techniques. In particular, formulas for all components of the transition dipole moment matrix elements within the CSF-based Table-CI method are derived and presented. Moreover, the flexibility of the recently introduced macroconfiguration description of model and external configuration spaces is shown to lead to multiple potential energy surfaces of sufficiently uniform quality to allow construction of useful Floquet states. The formalism and computer programs developed are demonstrated on Li2+ in a 0.9×1012 W/cm2 field. In analogy with Na2+, the 1,2 math, 1,2 math, 1 math, and 1 math states are of relevance, although the pattern of couplings is shown to be more complex. A hitherto unnoticed metastable state, which correlates asymptotically with 2 math, is described.
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31.15.vj Electron correlation calculations for atoms and ions: excited states
31.50.Df Potential energy surfaces for excited electronic states

Ab initio calculation of the C/D ratio of magnetic circular dichroism

Michael Seth, Tom Ziegler, and Jochen Autschbach

J. Chem. Phys. 122, 094112 (2005); http://dx.doi.org/10.1063/1.1856453 (7 pages) | Cited 9 times

Online Publication Date: 2 March 2005

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A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules.
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31.15.A- Ab initio calculations
33.55.+b Optical activity and dichroism
31.15.E- Density-functional theory
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry

Local-MP2 electron correlation method for nonconducting crystals

C. Pisani, M. Busso, G. Capecchi, S. Casassa, R. Dovesi, L. Maschio, C. Zicovich-Wilson, and M. Schütz

J. Chem. Phys. 122, 094113 (2005); http://dx.doi.org/10.1063/1.1857479 (12 pages) | Cited 84 times

Online Publication Date: 2 March 2005

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Rigorous methods for the post-HF (HF—Hartree–Fock) determination of correlation corrections for crystalline solids are currently being developed following different strategies. The CRYSTAL program developed in Torino and Daresbury provides accurate HF solutions for periodic systems in a basis set of Gaussian type functions; for insulators, the occupied HF manifold can be represented as an antisymmetrized product of well localized Wannier functions. This makes possible the extension to nonconducting crystals of local correlation linear scaling On techniques as successfully and efficiently implemented in Stuttgart’s MOLPRO program. These methods exploit the fact that dynamic electron correlation effects between remote parts of a molecule (manifesting as dispersive interactions in intermolecular perturbation theory) decay as an inverse sixth power of the distance R between these fragments, that is, much more quickly than the Coulomb interactions that are treated already at the HF level. Translational symmetry then permits the crystalline problem to be reduced to one concerning a cluster around the reference zero cell. A periodic local correlation program (CRYSCOR) has been prepared along these lines, limited for the moment to the solution of second-order Møller-Plesset equations. Exploitation of point group symmetry is shown to be more important and useful than in the molecular case. The computational strategy adopted and preliminary results concerning five semiconductors with tetrahedral structure (C, Si, SiC, BN, and BeS) are presented and discussed.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Nr Semiconductor compounds
71.20.Mq Elemental semiconductors
71.10.-w Theories and models of many-electron systems

Operator splitting algorithm for isokinetic SLLOD molecular dynamics

Guoai Pan, James F. Ely, Clare McCabe, and Dennis J. Isbister

J. Chem. Phys. 122, 094114 (2005); http://dx.doi.org/10.1063/1.1858861 (9 pages) | Cited 13 times

Online Publication Date: 2 March 2005

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We apply an operator splitting method to develop a simulation algorithm that has complete analytical solutions for the Gaussian thermostated SLLOD equations of motion [ D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984) ] for a system under shear. This leads to a homogeneous algorithm for performing both equilibrium and nonequilibrium isokinetic molecular dynamics simulation. The resulting algorithm is computationally efficient. In particular, larger integration time steps can be used compared to simulations with regular Gaussian thermostated SLLOD equations of motion. The utility and accuracy of the algorithm are demonstrated through application to the Weeks–Chandler–Anderson fluid. Although strict conservation of the kinetic energy suppresses thermal fluctuations in the system, this algorithm does not allow simulations at lower shear rates than those normally afforded by older nonequilibrium molecular dynamics simulations.
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61.20.Ja Computer simulation of liquid structure
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.60.-k Transport processes

The merits of the frozen-density embedding scheme to model solvatochromic shifts

Johannes Neugebauer, Manuel J. Louwerse, Evert Jan Baerends, and Tomasz A. Wesolowski

J. Chem. Phys. 122, 094115 (2005); http://dx.doi.org/10.1063/1.1858411 (13 pages) | Cited 52 times

Online Publication Date: 3 March 2005

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We investigate the usefulness of a frozen-density embedding scheme within density-functional theory [ J. Phys. Chem. 97, 8050 (1993) ] for the calculation of solvatochromic shifts. The frozen-density calculations, particularly of excitation energies have two clear advantages over the standard supermolecule calculations: (i) calculations for much larger systems are feasible, since the time-consuming time-dependent density functional theory (TDDFT) part is carried out in a limited molecular orbital space, while the effect of the surroundings is still included at a quantum mechanical level. This allows a large number of solvent molecules to be included and thus affords both specific and nonspecific solvent effects to be modeled. (ii) Only excitations of the system of interest, i.e., the selected embedded system, are calculated. This allows an easy analysis and interpretation of the results. In TDDFT calculations, it avoids unphysical results introduced by spurious mixings with the artificially too low charge-transfer excitations which are an artifact of the adiabatic local-density approximation or generalized gradient approximation exchange-correlation kernels currently used. The performance of the frozen-density embedding method is tested for the well-studied solvatochromic properties of the n→π* excitation of acetone. Further enhancement of the efficiency is studied by constructing approximate solvent densities, e.g., from a superposition of densities of individual solvent molecules. This is demonstrated for systems with up to 802 atoms. To obtain a realistic modeling of the absorption spectra of solvated molecules, including the effect of the solvent motions, we combine the embedding scheme with classical molecular dynamics (MD) and Car-Parrinello MD simulations to obtain snapshots of the solute and its solvent environment, for which then excitation energies are calculated. The frozen-density embedding yields estimated solvent shifts in the range of 0.20–0.26 eV, in good agreement with experimental values of between 0.19 and 0.21 eV.
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31.15.E- Density-functional theory
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.70.Dk Environmental and solvent effects
33.70.Jg Line and band widths, shapes, and shifts
34.70.+e Charge transfer
31.15.xv Molecular dynamics and other numerical methods

Describing static correlation in bond dissociation by Kohn–Sham density functional theory

M. Fuchs, Y.-M. Niquet, X. Gonze, and K. Burke

J. Chem. Phys. 122, 094116 (2005); http://dx.doi.org/10.1063/1.1858371 (13 pages) | Cited 43 times

Online Publication Date: 4 March 2005

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We show that density functional theory within the RPA (random phase approximation for the exchange-correlation energy) provides a correct description of bond dissociation in H2 in a spin-restricted Kohn–Sham formalism, i.e., without artificial symmetry breaking. We present accurate adiabatic connection curves both at equilibrium and beyond the Coulson–Fisher point. The strong curvature at large bond length implies important static (left–right) correlation, justifying modern hybrid functional constructions but also demonstrating their limitations. Although exact at infinite separation and accurate near the equilibrium bond length, the RPA dissociation curve displays unphysical repulsion at larger but finite bond lengths. Going beyond the RPA by including the exact exchange kernel (RPA+X), we find a similar repulsion. We argue that this deficiency is due to the absence of double excitations in adiabatic linear response theory. Further analyzing the H2 dissociation limit we show that the RPA+X is not size consistent, in contrast to the RPA.
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31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies
31.15.vn Electron correlation calculations for diatomic molecules
33.15.Dj Interatomic distances and angles
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Experiments and quantum-chemical calculations on Rydberg states of H2CS in the region 5.6–9.5 eV

Su-Yu Chiang and I-Feng Lin

J. Chem. Phys. 122, 094301 (2005); http://dx.doi.org/10.1063/1.1853380 (6 pages) | Cited 2 times

Online Publication Date: 24 February 2005

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Absorption spectrum of H2CS in the region 5.6–9.5 eV was recorded with a continuously tunable light source of synchrotron radiation. After we subtracted absorption bands of CS2, our spectrum clearly shows vibrational progressions associated with transitions math(π,π*)–X math and math(n,4s)–X math in the region 5.6–6.7 eV. A spectrum from which absorption of C2H4 and CS2 are subtracted shows several discrete bands in the region 6.9–9.5 eV. A Rydberg state math(n,4pz) lying below Rydberg state math(n,4py) is confirmed, and the C–H symmetric stretching (ν1) and CH out-of-plane bending (ν4) modes for a transition math(n,4s)–X math are identified. New transitions to Rydberg states associated with excitation to 5s-11s, 5pz-7pz, 5py-7py, and 3d-6d are identified based on quantum defects and comparison with vertical excitation energies predicted with time-dependent density-functional theory (TD-DFT) and outer-valence Green’s-function (OVGF) methods. For lower excited states predictions from these TD-DFT/6-31+G calculations agree satisfactorily with experimental values, but for higher Rydberg states the OVGF method using aug-cc-pVTZ basis set augmented with extra diffuse functions yields more accurate predictions of excitation energies.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Fm Bond strengths, dissociation energies
33.80.-b Photon interactions with molecules
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.E- Density-functional theory

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

Matthias Zierhut, Bastian Noller, Thomas Schultz, and Ingo Fischer

J. Chem. Phys. 122, 094302 (2005); http://dx.doi.org/10.1063/1.1857475 (7 pages) | Cited 12 times

Online Publication Date: 25 February 2005

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The excited state decay of the hydrocarbon radicals ethyl, C2H5; propargyl, C3H3; and benzyl, C7H7 was investigated by femtosecond time-resolved photoionization. Radicals were generated by flash pyrolysis of n-propyl nitrite, propargyl bromide, and toluene, respectively. It is shown that the 2 math (3s) Rydberg state of ethyl excited at 250 nm decays with a time constant of 20 fs. No residual signal was observed at longer delay times. For the 3 math state of propargyl excited at 255 nm a slower decay with a time constant 50±10 fs was determined. The 4 math state of benzyl excited at 255 nm decays within 150±30 fs.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Structures of [(CO2)n(H2O)m]− (n = 1–4, m = 1,2) cluster anions. I. Infrared photodissociation spectroscopy

Azusa Muraoka, Yoshiya Inokuchi, Nobuyuki Nishi, and Takashi Nagata

J. Chem. Phys. 122, 094303 (2005); http://dx.doi.org/10.1063/1.1850896 (7 pages) | Cited 2 times

Online Publication Date: 25 February 2005

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The infrared photodissociation spectra of [(CO2)n(H2O)m]− (n = 1–4, m = 1, 2) are measured in the 3000–3800 cm−1 range. The [(CO2)n(H2O)1]− spectra are characterized by a sharp band around 3570 cm−1 except for n = 1; [(CO2)1(H2O)1]− does not photodissociate in the spectral range studied. The [(CO2)n(H2O)2]− (n = 1, 2) species have similar spectral features with a broadband at ≈ 3340 cm−1. A drastic change in the spectral features is observed for [(CO2)3(H2O)2]−, where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm−1. Ab initio calculations are performed at the MP2/6-311++G** level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO2)n(H2O)m]− species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO2)n(H2O)m]−: (1) the incorporated H2O is bonded to either CO2− or C2O4− through two equivalent OH⋯O hydrogen bonds to form a ring structure in [(CO2)n(H2O)1]−; (2) two H2O molecules are independently bound to the O atoms of CO2− in [(CO2)n(H2O)2]− (n = 1, 2); (3) a cyclic structure composed of CO2− and two H2O molecules is formed in [(CO2)3(H2O)2]−.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Ea Infrared spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.A- Ab initio calculations
33.20.Tp Vibrational analysis
33.15.Fm Bond strengths, dissociation energies

The singlet electronic ground state isomers of dialuminum monoxide: AlOAl, AlAlO, and the transition state connecting them

Justin M. Turney, Levent Sari, Yukio Yamaguchi, and Henry F. Schaefer

J. Chem. Phys. 122, 094304 (2005); http://dx.doi.org/10.1063/1.1850098 (12 pages) | Cited 3 times

Online Publication Date: 25 February 2005

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The singlet electronic ground state isomers, math math (AlOAl D∞h) and math math (AlAlO C∞ν), of dialuminum monoxide have been systematically investigated using ab initio electronic structure theory. The equilibrium structures and physical properties for the two molecules have been predicted employing self-consistent field (SCF) configuration interaction with single and double excitations (CISD), multireference CISD (MRCISD), coupled cluster with single and double excitations (CCSD), CCSD with perturbative triples [CCSD(T)], CCSD with iterative partial triple excitations (CCSDT-3 and CC3), and full triples (CCSDT) coupled cluster methods. Four correlation consistent polarized valence (cc-pVXZ) type basis sets were used. The AlAlO system is rather challenging theoretically. The two isomers are confirmed to have linear structures at all levels of theory. The symmetric isomer AlOAl is predicted to lie 81.9 kcal mol−1 below the asymmetric isomer AlAlO at the cc-pV(Q+d)Z CCSD(T) level of theory. The predicted harmonic vibrational frequencies for the math math AlOAl molecule, ω1 = 517 cm−1, ω2 = 95 cm−1, and ω3 = 1014 cm−1, are in good agreement with experimental values. The harmonic vibrational frequencies for the math math AlAlO structure, ω1 = 1042 cm−1, ω2 = 73 cm−1, and ω3 = 253 cm−1, presently have no experimental values with which to be compared. With the same methods the barrier heights for the isomerization AlOAl→AlAlO and AlAlO→AlOAl reactions were predicted to be 84.3 and 2.4 kcal mol−1, respectively. The dissociation energies D0 for AlOAl (math math) and AlAlO (math math)→AlO (X math)+Al (math) were determined to be 130.8 and 48.9 kcal mol−1, respectively. Thus, both symmetric AlOAl (math math) and asymmetric AlAlO (math math) isomers are expected to be thermodynamically stable with respect to the dissociation into AlO (X math) + Al (math) and kinetically stable for the isomerization reaction (AlAlO→AlOAl) at sufficiently low temperatures.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
82.30.Qt Isomerization and rearrangement
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
31.15.bw Coupled-cluster theory
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