Accurately solving the electronic Schrödinger equation of atoms and molecules using explicitly correlated (r12-) multireference configuration interaction. VII. The hydrogen fluoride molecule

Matsunaga

et al. 2007

The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F2molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spinorbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion. The nonrelativistic, valence-shell-only-correlated ab initio potential energy curve of the F 2 molecule, which was reported in the preceding paper, is complemented by determining the energy contributions that arise from the electron correlations that involve the core electrons as well as the contributions that are due to spin-orbit coupling and scalar relativistic effects. The dissociation curve rises rather steeply toward the energy of the dissociated atoms because, at larger distances, the atomic quadrupole-quadrupole repulsion and spin-orbit coupling counteract the attractive contributions from incipient covalent binding and correlation forces including dispersion.

Section: Discussionsupporting

confidence: 76%

Accurate ab initio potential energy curve of F2. II. Core-valence correlations, relativistic contributions, and long-range interactions

Matsunaga

et al. 2007

“…This importance of the higher-order corrections is in agreement with the observations of other researchers. 46,50,127 Vibrational spectra of diatomic molecules probably furnish the most exacting data available for probing energetic changes along entire reaction paths. They present therefore good tests for ab initio methods that aim at describing reaction paths.…”

Section: Discussionmentioning

confidence: 99%

“…The HF molecule has been treated in several studies. [47][48][49][50] The best of these, by Cardoen and Gdanitz,50 includes core correlations and relativistic effects. The mean absolute deviation is 21 cm −1 for the 19 vibrational energy transitions from the lowest level, the maximum deviation from experiment of 77 cm −1 occurring for the highest level, v = 19.…”

Section: Introductionmentioning

confidence: 99%

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

Matsunaga

et al. 2007

134

An analytical expression is found for the accurate ab initiopotential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5cm−1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30cm−1 of the experimental value of 12953±8cm−1. The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation,spin-orbit coupling, and scalar relativity. The Dunham analysis [Phys. Rev.41, 721 (1932)] of the spectrum is found to be very accurate. New values are given for the spectroscopic constants. KeywordsAb initio calculations, Dissociation energies, Polynomials, Dissociation, Electron correlation calculations Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 127 (2007) An analytical expression is found for the accurate ab initio potential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F 2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5 cm −1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30 cm −1 of the experimental value of 12 953± 8 cm −1 . The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation, spin-orbit coupling, and scalar relativity. The Dunham analysis ͓Phys. Rev. 41, 721 ͑1932͔͒ of the spectrum is found to be very accurate. New values are given for the spectroscopic constants.

“…These methods yield indeed very accurate energies, but studies of potential energy surfaces are as yet rare. 97 In a series of recent papers, [98][99][100][101][102] we have introduced another strategy for accurately approximating full CI energies, the correlation energy extrapolation by intrinsic scaling ͑CEEIS͒. It can be used with single-as well as multiconfigurational zeroth-order reference functions; it systematically approximates the full CI limit while monitoring the closeness of this approximation along the way; it uses standard computational CI machinery and its efficiency is increased by the parallelization of these codes.…”

Section: Introductionmentioning

confidence: 99%

“…[79][80][81][82][83][84][85][86][87][88] Hylleraas 89 was the first to show that this problem can be greatly alleviated by the explicit inclusion of the interelectronic distance in the wavefunctions for He and H 2 . More recently, a number of authors have succeeded in adapting this approach to the general case of many-electron systems, [90][91][92][93][94][95][96][97] notwithstanding nontrivial algorithmic complexities. These methods yield indeed very accurate energies, but studies of potential energy surfaces are as yet rare.…”

Section: Introductionmentioning

confidence: 99%

Accurate ab initio potential energy curve of F2. I. Nonrelativistic full valence configuration interaction energies using the correlation energy extrapolation by intrinsic scaling method

Gordon

et al. 2007

The recently introduced method of correlationenergy extrapolation by intrinsic scaling (CEEIS) is used to calculate the nonrelativistic electron correlations in the valence shell of the F2 molecule at 13 internuclear distances along the ground state potential energy curve from 1.14Åto8Å, the equilibrium distance being 1.412Å. Using Dunning's correlation-consistent double-, triple-, and quadruple-zeta basis sets, the full configuration interaction energies are determined, with an accuracy of about 0.3mhartree, by successively generating up to octuple excitations with respect to multiconfigurational reference functions that strongly change along the reaction path. The energies of the reference functions and those of the correlationenergies with respect to these reference functions are then extrapolated to their complete basis set limits. The applicability of the CEEIS method to strongly multiconfigurational reference functions is documented in detail. The recently introduced method of correlation energy extrapolation by intrinsic scaling ͑CEEIS͒ is used to calculate the nonrelativistic electron correlations in the valence shell of the F 2 molecule at 13 internuclear distances along the ground state potential energy curve from 1.14 Å to 8 Å, the equilibrium distance being 1.412 Å. Using Dunning's correlation-consistent double-, triple-, and quadruple-zeta basis sets, the full configuration interaction energies are determined, with an accuracy of about 0.3 mhartree, by successively generating up to octuple excitations with respect to multiconfigurational reference functions that strongly change along the reaction path. The energies of the reference functions and those of the correlation energies with respect to these reference functions are then extrapolated to their complete basis set limits. The applicability of the CEEIS method to strongly multiconfigurational reference functions is documented in detail.