Ab initio study of chlorosilanes: Dipole moments and charge distributions

Dipole moments of chlorosilane derivatives have been investigated at SCF, M P2, CISD, and CCD levels of ab initio theories with various basis sets. Cal culated dipole moments of chlorosilanes are quite dependent on the size of the basis sets, and most calculations with modest basis sets significantly overestimate the experimental values. To predict dipole moments of chlorosi lanes reasonably, extremely large sizes of the basis set, for example, 6-31 1++G(3df,2p), are required. Incorporation of electron correlation improves calculated dipole moments somewhat, but the degree of the improvement seems to be limited without an employment of remarkably large basis sets. Our an alyses by using electrostatic potentials and CHELPG charges show that the m agnitudes of calculated dipole moments in chlorosilanes have a close relati on with the degree of the charge separation across polar bonds, including t he Si-Cl bond.