SPIN-ORBIT EFFECTS ON STRUCTURES OF CLOSED-SHELL POLYATOMIC-MOLECULESCONTAINING HEAVY-ATOMS CALCULATED BY 2-COMPONENT HARTREE-FOCK METHOD

We have implemented geometry optimization using an analytic gradient t o a two-component Kramers' restricted Hartree-Fock (KRHF) method for p olyatomic molecules with closed-shell configurations, The KRHF method is a Hartree-Fock method based on relativistic effective core potentia ls with effective spin-orbit operators. The derivatives of spin-orbit integrals are obtained by numerical differentiation. Geometries for th e various forms of polyatomic hydrides containing row 6 p-block elemen ts are optimized with and without spin-orbit interactions. The structu ral changes due to spin-orbit interactions are small, but show definit e trends, which correlate well with the p(1/2) spinor population. Atom ization energies are reduced significantly by incorporating spin-orbit interactions for all molecules considered. The KRHF calculations of s everal methylhalides demonstrate that the spinor energies from the KRH F method can be useful for the interpretation of experimental photoele ctron spectra of molecules exhibiting spin-orbit splittings. (C) 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1526-1533, 1998.