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Unexpected CASSCF bistability phenomenon
Author(s) -
Guihery Nathalie,
Malrieu JeanPaul,
Maynau Daniel,
Handrick Klaus
Publication year - 1997
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/(sici)1097-461x(1997)61:1<45::aid-qua5>3.0.co;2-4
Subject(s) - diradical , complete active space , space (punctuation) , bistability , wave function , domain (mathematical analysis) , chemistry , field (mathematics) , computational chemistry , physics , quantum mechanics , mathematics , density functional theory , mathematical analysis , pure mathematics , computer science , basis set , singlet state , excited state , operating system
One exhibits a problem in which two strongly nonorthogonal complete active‐space self‐consistent field (CASSCF) solutions are obtained. The problem concerns a molecular frame which presents two stable geometries at the CASSCF level, quinoidal and diradical forms, in disagreement with experiment which indicates a unique minimum corresponding to an intermediate geometry. Those two stable solutions are obtained in a significant domain of intermediate geometries and are related with the CASSCF wave functions of the two stable structures. Obtaining a reliable potential surface starting from CASSCF solutions (even from larger CAS) appears as a very difficult task. © 1997 John Wiley & Sons, Inc.