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Effective handling of a large configuration state function expansion for an MCSCF state and improved efficiency for two‐electron integral transformations in MCSCF
Author(s) -
Olsen Jeppe,
Yeager Danny L.
Publication year - 1983
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.560230304
Subject(s) - transformation (genetics) , chemistry , projection (relational algebra) , state (computer science) , configuration interaction , function (biology) , complement (music) , computational chemistry , state space , mathematics , computer science , algorithm , molecule , biochemistry , statistics , organic chemistry , evolutionary biology , complementation , biology , gene , phenotype
Effective solutions for two difficulties which may be present in MCSCF calculation are discussed: (i) We show how the large configuration state function state expansion case may be handled simply and effectively without the introduction of extraneous projection operators or Lagrange multipliers; (ii) we present a simplified two‐electron integral transformation procedure which significantly reduces the operation count (and hence computational efficiency is increased) for second order and particularly for third order MCSCF procedures. The procedures we introduce use some freedom available in the orthogonal complement Cl space and the virtual orbital space to simplify MCSCF calculations.