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Ab‐initio and approximately rigorous calculations on small, medium, and large systems
Author(s) -
Kaufman Joyce J.,
Popkie Herbert E.,
Preston Harry J. T.
Publication year - 1977
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.560110613
Subject(s) - ab initio , diatomic molecule , ab initio quantum chemistry methods , chemistry , computational chemistry , molecule , valence (chemistry) , atomic physics , valence electron , molecular orbital , electron , molecular physics , physics , quantum mechanics , organic chemistry
We have explored two areas of approximately rigorous calculations for computing nonempirical wave functions for heavy and/or large molecules orders of magnitude faster than with conventional ab ‐ initio methods but with the same chemical accuracy. First, we have developed and used a series of programs (starting from our new fast sets of ab ‐ initio Gaussian SCF and SCF ‐ CI programs) incorporating ab ‐ initio effective core model potentials ( MOD ‐ POT ) which allow one to treat only the valence electrons explicitly, plus a charge conserving integral prescreening, which cuts down significantly on the number of integrals that have to be calculated, stored, or processed for a large molecule. We have named this latter procedure VRDDO (variable retention of diatomic differential overlap). With these MODPOT and MODPOT / VRDDO methods we have explored a variety of small, medium, and large systems ranging from electron affinities of atoms through to molecules of biological interest and large boron hydrides. The results compared to ab ‐ initio SCF or SCF / CI calcuations are very good, usually within 0.001 to 0.002 a.u. for orbital energies and gross atomic populations ( GAPS ) and even better along potential energy curves. Secondly, we have explored the use of the MS ‐ X α method for less conventional molecules and properties than those for which it is customarily employed.