An electron pair operator approach to coupled cluster wave functions. Application to He2, Be2, and Mg2and comparison with CEPA methods

1981 ◽  
Vol 74 (8) ◽  
pp. 4544-4556 ◽  
Author(s):  
Richard A. Chiles ◽  
Clifford E. Dykstra
Keyword(s):  
Electron Pair ◽  
Wave Functions ◽  
Coupled Cluster ◽  
Operator Approach

scholarly journals Exact parameterization of fermionic wave functions via unitary coupled cluster theory

2019 ◽  
Vol 151 (24) ◽  
pp. 244112 ◽  
Author(s):  
Francesco A. Evangelista ◽  
Garnet Kin-Lic Chan ◽  
Gustavo E. Scuseria
Keyword(s):  
Wave Functions ◽  
Coupled Cluster ◽  
Coupled Cluster Theory ◽  
Cluster Theory

scholarly journals General Framework for Calculating Spin–orbit Couplings Using Spinless One-Particle Density Matrices: Theory and Application to the Equation-of-Motion Coupled-Cluster Wave Functions

2019 ◽  
Author(s):  
Pavel Pokhilko ◽  
Evgeny Epifanovsky ◽  
Anna I. Krylov
Keyword(s):  
Degrees Of Freedom ◽  
Particle Density ◽  
Mean Field ◽  
Transition Density ◽  
Open Shell ◽  
Equation Of Motion ◽  
Wave Functions ◽  
Coupled Cluster ◽  
Spin Orbit ◽  
Matrix Elements

Standard implementations of non-relativistic excited-state calculations compute only one component of spin multiplets (i.e., Ms =0 triplets), however, matrix elements for all components are necessary for calculations of experimentally relevant spin-dependent quantities. To circumvent explicit calculations of all multiplet components, we employ Wigner–Eckart’s theorem. Applied to a reduced one-particle transition density matrix computed for a single multiplet component, Wigner–Eckart’s theorem generates all other spin–orbit matrix elements. In addition to computational efficiency, this approach also resolves the phase issue arising within Born–Oppenheimer’s separation of nuclear and electronic degrees of freedom. A general formalism and its application to the calculations of spin–orbit couplings using equation-of-motion coupled-cluster wave functions is presented. The two-electron contributions are included via the mean-field spin–orbit treatment. Intrinsic issues of constructing spin–orbit mean-field operators for open-shell references are discussed and a resolution is proposed. The method is benchmarked by using several radicals and diradicals. The merits of the approach are illustrated by a calculation of the barrier for spin inversion in a high-spin tris(pyrrolylmethyl)amine Fe(II) complex.

Computing coupled-cluster wave functions with arbitrary excitations

2000 ◽  
Vol 113 (4) ◽  
pp. 1359-1365 ◽  
Author(s):  
Mihály Kállay ◽  
Péter R. Surján
Keyword(s):  
Wave Functions ◽  
Coupled Cluster
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