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New implementation of the graphical unitary group approach for multireference direct configuration interaction calculations
Author(s) -
Lischka Hans,
Shepard Ron,
Brown Franklin B.,
Shavitt Isaiah
Publication year - 2009
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.560200810
Subject(s) - multireference configuration interaction , hamiltonian matrix , unitary state , rotation formalisms in three dimensions , hamiltonian (control theory) , configuration interaction , unitary group , eigenvalues and eigenvectors , computer science , group (periodic table) , computational science , computational chemistry , chemistry , quantum mechanics , physics , symmetric matrix , mathematics , molecule , mathematical optimization , geometry , political science , law
Improved procedures were used in a new computer implementation of the graphical unitary group approach, designed specifically for efficient multireference configuration interaction calculations for molecules. These procedures include improvements in the treatment of spatial symmetry and of the multireference interacting space, and include the “repartitioned Hamiltonian,” which provides a flexible alternative to conventional particle‐hole formalisms. The new computer programs avoid the construction of very long formula files, and leave the matrix eigenvector iterations as the only significant rate‐determining step in large‐scale direct CI calculations.