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Modified virtual orbitals ( MVO ) in limited CI calculations
Author(s) -
Wasilewski J.
Publication year - 1991
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/qua.560390502
Subject(s) - atomic orbital , eigenfunction , valence (chemistry) , ionic bonding , basis set , operator (biology) , chemistry , atomic physics , ionization , molecular orbital , ion , computational chemistry , physics , molecule , quantum mechanics , density functional theory , biochemistry , eigenvalues and eigenvectors , repressor , transcription factor , gene , electron
A modification of virtual orbitals seems to be an inexpensive way of calculating a large part of the correlation energy. Three types of MVOS have been compared in this paper, on the basis of limited valence‐shell CI calculations for some lower states of the H 2 O molecule: A — orthogonalized eigenfunctions of exchange operators; B — eigenfunctions of one combined exchange operator; C — eigenfunctions of the Fock operator for a highly ionized system. For small virtual spaces (20% of available orbitals used), approach C gives 70% of E corr CI‐SD , being superior to the two other approaches. When using only 50% of MVOS , all the three types of approaches result in calculating 90% of E corr CI‐SD , but the ionic orbitals give a better description of the state separations.