A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride

[img]PDF - Authorized users only
Language: English
806Kb
Title:A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride
Creators:
Nooijen, Marcel
Shamasundar, K. R.
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 70, 8, pp. 1082-1108
Uncontrolled Keywords:<i>Ab initio</i> calculations, CCSD, Hamiltonian, Multireference methods, Coupled clusters, Quantum chemistry

Abstract

State-specific Brueckner equation-of-motion coupled-cluster theory (SS-B-EOMCC) is summarized, which can be considered an internally contracted version of a state-selective multireference coupled-cluster theory, which, however, is not entirely size-consistent. The method is applicable to general multireference problems, adheres to the space and spin symmetries of the molecular system, is straightforwardly extended to a state-averaged version, and has an associated perturbative variant which yields results close to the full coupled-cluster treatment. A key strength is that Brueckner orbitals are used, such that orbitals are optimized in the presence of dynamic correlation. A number of variations on the theme of SS-EOMCC is applied to study the ionic-covalent avoided crossing in LiF in a 6-311++G(3df,3pd) basis set. While reasonable results are obtained at the state-averaged level, the iterative solution process does not consistently converge for SS-EOMCC, due to the non-Hermiticity of the transformed Hamiltonian which may yield complex eigenvalues upon truncated diagonalization. This leads to an irrevocable breakdown of the state-specific EOMCC approach. We indicate some future directions that can resolve some of the problems with the SS-EOMCC methodology, as revealed by the demanding test case of the LiF potential energy curves. <p>

Title:A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride
Creators:
Nooijen, Marcel
Shamasundar, K. R.
Uncontrolled Keywords:<i>Ab initio</i> calculations, CCSD, Hamiltonian, Multireference methods, Coupled clusters, Quantum chemistry
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:70
Number:8
Page Range:pp. 1082-1108
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20051082UNSPECIFIED
ID Code:2406
Item Type:Article
Deposited On:06 Feb 2009 17:18
Last Modified:06 Feb 2009 16:18

Citation

Nooijen, Marcel; Shamasundar, K. R. (2005) A Case Study of State-Specific and State-Averaged Brueckner Equation-of-Motion Coupled-Cluster Theory: The Ionic-Covalent Avoided Crossing in Lithium Fluoride. Collection of Czechoslovak Chemical Communications, 70 (8). pp. 1082-1108. ISSN 0010-0765

Repository Staff Only: item control page