Premium
Usefulness of modified virtual orbitals in multireference CI procedure illustrated by calculations on lithium clusters
Author(s) -
Fantucci P.,
BonačiCćKoutecký V.,
Koutecký J.
Publication year - 1985
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540060515
Subject(s) - atomic orbital , wave function , lithium (medication) , coupled cluster , chemistry , atomic physics , basis set , computational chemistry , physics , electron , quantum mechanics , density functional theory , molecule , medicine , endocrinology
The maximization of the exchange interaction between the canonical Hartree–Fock virtual and occupied orbitals leads to a transformed set of virtual orbitals which are well suited as one‐electron functions for CI calculations. The procedure, generally known for a long time is seldom applied, despite its simplicity and very low computational demand. However, it is found to be particularly useful in the case of multireference CI, since an improved energy is obtained with a considerable shortening of the CI expansion. Moreover, in the final CI wave function, several configurations appear with considerable weight, thus allowing an easy choice of additional configurations to be inserted in the definition of a new zero‐order wave function. The efficiency of the computational procedure is discussed for the case of a Li 6 cluster of D 3 h symmetry and for the NaCO and PdCO complexes. Results are reported for the relative stability of four different geometrical arrangements of the Li 6 cluster.