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On the internally contracted multireference CI method with full contraction
Author(s) -
Siegbahn Per E. M.,
Svensson Mats
Publication year - 1992
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.560410114
Subject(s) - multireference configuration interaction , unitary state , chemistry , computational chemistry , contraction (grammar) , atomic physics , physics , density functional theory , basis set , medicine , political science , law
The configuration interaction ( CI ) method where the efficiency of the generators of the unitary group is most fully exploited is the internally contracted multireference CI method. In the most recent version of this method the semi‐internal configurations were kept uncontracted, which means that the number of configurations can still be quite large. In the present study the necessary formulas are derived for the case where the semi‐internal states are also contracted. The highest density matrix that appears in these formulas is of order 5, and the computational treatment of this large matrix is discussed in detail.