Efficient generation of matrix elements for one-electron spin-orbit operators

We present a procedure for the generation of spin-couplings with effective one-electron spin-orbit operators over spin-symmetry-adapted functions that is independent of the size of the internal space. Extending a spin-free approach by Wetmore and Segal [Chem. Phys. Lett. 36 (1975) 478], we show that all couplings may be precomputed once and stored as a program library. Storage requirements are minimal for up to 10 open shells and become manageable for up to 12 open shells by storing sparse matrices. The procedure has been implemented in the new Spin-Orbit Couplig Kit SPOCK, based on an individually selecting configuration interaction program. Benchmark and test calculations have been performed on third row atoms and porphyrin derivates