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5159868 
Journal Article 
Analytical second derivatives for excited electronic states using the single excitation configuration interaction method: theory and application to benzo[a]pyrene and chalcone 
Maurice, D; Head-Gordon, M 
1999 
1 
Molecular Physics
ISSN: 0026-8976
EISSN: 1362-3028 
TAYLOR & FRANCIS LTD 
LONDON 
96 
10 
1533-1541 
English 
WOS:000080426500009 
A compact formulation and a semi-direct implementation are described of analytical second derivatives of the single excitation configuration interaction (CIS) energy. CPU time, memory usage and disc storage all scale with the same power of system size as the ground state Hartree—Fock (HF) method, with a coefficient only 2 to 3 times larger. Thus usually analytical excited state CIS frequencies are feasible when HF frequencies are feasible. As a computational example, analytical CIS/3-21G frequencies for benzo[a]pyrene are calculated more efficiently than with finite differences. As a chemical application, analytical CIS/6-31G* frequencies are used to investigate non-planarity in the lowest π → π excited state of transchalcone. © 1999 Taylor & Francis Group, LLC.