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  • Title: Spin-orbit coupling of DFT/MRCI wavefunctions: method, test calculations, and application to thiophene.
    Author: Kleinschmidt M, Tatchen J, Marian CM.
    Journal: J Comput Chem; 2002 Jun; 23(8):824-33. PubMed ID: 12012359.
    Abstract:
    During the past decade the one-center mean-field approximation has proven to be a very appropriate framework for the accurate description of spin-orbit effects at the correlated all-electron level. Here, a new efficient code, SPOCK, is introduced that calculates spin-orbit matrix elements in the one-center mean-field approximation for multireference CI wave functions. For the first time, the computation of spin-dependent interactions within a Kohn-Sham orbital based CI (DFT/MRCI) scheme1 is made possible. The latter approach is suitable for large scale systems with up to 100-200 valence electrons. Test calculations are performed on well-known diatomic molecules and the thiocarbonyl pyranthione. Spin-orbit matrix elements show good agreement with their Hartree-Fock orbital based counterparts but are obtained at considerably lower expense, thus demonstrating the power of the method. As an application singlet-triplet couplings in thiophene are investigated that are important for the photophysics and photochemistry. Spin-orbit matrix elements between all pi --> pi* excited states are found to be small. Considerably larger spin-orbit matrix elements are observed only for cases in which pi --> sigma* excited configurations are involved.
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