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A spin‐adapted coupled‐cluster based linear response theory for double ionization potentials
Author(s) -
Chaudhuri R.,
Datta B.,
Das K.,
Mukherjee D.
Publication year - 1996
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1996)60:1<347::aid-qua34>3.0.co;2-8
Subject(s) - coupled cluster , ionization , atomic physics , cluster (spacecraft) , ionization energy , auger , spin (aerodynamics) , chemistry , physics , quantum mechanics , molecule , ion , computer science , thermodynamics , programming language
We developed in this article a spin‐adapted formulation of the coupled‐cluster based linear response theory (CC‐LRT) for computing double‐ionization potentials (DIPs), which may be experimentally observed by Auger spectroscopy. CC‐LRT is a multireference generalization of the CC theory where the energy differences have no disconnected vacuum (core) diagrams, signifying core‐extensivity. For the spin‐adaptation of the CC‐LRT equations for the singlet and triplet manifolds, we used the Young‐Yamanouchi orthogonal spin‐eigenfunctions. The orbital version of the CC‐LRT equations are then automatically generated by the conjugate projection operators of Young‐Yamanouchi spin functions. We illustrated the working of our spin‐adaptation procedure by confining our CC‐LRT equations to the space of 2 h and 1 p –3 h ionized determinants. As numerical application of our formalism, we computed the Auger kinetic energies of HF and H 2 O. We also analyzed the nature of size‐extensivity of the DIPs generated by CC‐LRT and showed explicitly that when the molecule is composed of two noninteracting fragments the computed DIPs are either DIPs of fragment A or B or a composite DIP depending on both A and B, which are just not sum of ionization potentials (IPs) of A and B. This analysis is done to underscore the fact that DIPs from CC‐LRT is only core‐extensive and not fully extensive. © 1996 John Wiley & Sons, Inc.