Formulation of the direct configuration interaction method for triplet spin states. Applications to glyoxal
- 15 January 1978
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 68 (2) , 769-774
- https://doi.org/10.1063/1.435751
Abstract
The direct CI method developed by Roos and Siegbahn has been extended to triplet spin states. Included in the CI are all single excitations plus all doubly excited configurations having nonzero Hamiltonian matrix elements with the Hartree–Fock reference configuration. The new method has been implemented as a part of the b e r k e l e y system of minicomputer‐based programs. Applications to the 3Au(n→π*), 3Bg(n→π*), and 3Bu(π→π*) states of glyoxal (HCO)2 are presented. Some modifications, following Bender’s vector method, of the original Roos method for closed‐shell singlets are also discussed. These have allowed us to determine fully variational CI wavefunctions including as many as 15 006 configurations (42 456 Slater determinants).Keywords
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