EOMCC over excited state Hartree-Fock solutions (ESHF-EOMCC): An efficient approach for the entire ground state potential energy curves of higher-order bonds

Abstract

The equation-of-motion coupled cluster (EOMCC) method based on the excited state Hartree-Fock (ESHF) solutions is shown to be appropriate for computing the entire ground state potential energy curves of strongly correlated higher-order bonds. The new approach is best illustrated for the homolytic dissociation of higher-order bonds in molecules. The required multireference character of the true ground state wavefunction is introduced through the linear excitation operator of the EOMCC method. Even at the singles and doubles level of cluster excitation truncation, the nonparallelity error of the ground state potential energy curve from the ESHF based EOMCC method is small. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx

Barrierless association of CF 2 and dissociation of C 2 F 4 by variational transition-state theory and system-specific quantum Rice–Ramsperger–Kassel theory

“…Bond dissociation is usually an intrinsically multiconfigurational problem, often called a multireference problem (1). Coupled cluster (CC) theory (2, 3), as a high-level single-reference wave function method, is able to provide fairly accurate energies for bond-dissociation processes only if a high-enough excitation level (such as quadruple excitations) is used for the cluster operatorT; however, lack of such expensive higher excitation operators in CC calculations [such as in the case of coupled-cluster theory with single and double excitations (CCSD) (4)] can lead to a significant unphysical bump (5,6) in the potential energy curve for dissociation. Kohn-Sham density functional theory (KS-DFT) (7,8), however, with carefully chosen exchange correlation (XC) density functionals can produce smooth potential curves for dissociation with satisfactory accuracy without introducing any unphysical bump and with much smaller computational cost; however, at this time, an XC functional that can be used as a panacea does not exist.…”