We have implemented a complete active space configuration interaction method (CASCI) based on floating occupation molecular orbitals (FOMOs) at the ab initio level. The performance of this FOMO-CASCI method was investigated for potential applications in photochemistry and photodynamics. We found that FOMO-CASCI often represents a good approximation to the state-averaged complete active space self-consistent field (SA-CASSCF) method. FOMO-CASCI is therefore an attractive alternative for use in ab initio photodynamics. The method is more efficient and more stable than SA-CASSCF. We also discuss some problematic cases for the FOMO-CASCI approach. Possible extensions of the FOMO-CASCI approach are discussed briefly.

Department of Physical Chemistry Institute of Chemical Technology Prague 166 28 Prague 6 Czech Republic

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