Nonlinear optical properties of threefold coordinated paramagnetic Si centers: An ab initio time-dependent Hartree-Fock study on SiH3 radical

Static and dynamic (hyper)polarizabilities of SiH3 radical have been calcul ated by ab initio time-dependent unrestricted Hartree-Fock method with the use of a double-zeta plus polarization basis set. In order to examine the e ffect of a Si dangling bond on the polarizabilities, calculations have also been performed on the diamagnetic SiH4 molecule using the same method and the basis set. A comparison of the polarizabilities of the two systems reve als that a dangling bond at the Si atom causes only a minor change in the v alue of polarizability, alpha. However, a Si-dangling bond in the case of S iH3 distorts the symmetry in the charge distribution in such a way that the dipole moment, mu, and the first-hyperpolarizability coefficient, beta, be come nonzero. The calculations also reveal that the contributions of the al pha-spin electrons sind alpha-spin electrons to (hyper)polarizabilities of the SiH3 radical substantially differ from each other. The magnitude of hyp erpolarizability coefficient is found to be determined by the contributions from different spins.