{\em Ab Initio} Study of Atomic and Molecular Polarizabi-lities

We calculate the static electric dipole polarizabilities for a variety of atoms and molecules using a finite field method implemented in the framework of an {\it ab initio} density functional formalism. Our calculations employ several different representations of the exchange-correlation potential, including the local density approximation, generalized gradient approximation, and asymptotically correct functionals introduced by Leeuwen-Baerends [1] and Casida-Salahub [2]. We observe that the computed values of polarizabilities are strongly influenced by the asymptotic behavior of the density functional exchange-correlation potential. The accuracy of theoretical atomic and molecular polarizabilities is substantially improved by the use of asymptotically correct exchange-correlation functionals. This result can be explained in terms of electronic excitation energies and the polarizability sum rule.\\[0pt] [1] R. van Leeuwen and E. J. Baerends, Phys. Rev. A 49, 2421 (1994).\\[0pt] [2] M. E. Casida and D. R. Salahub, J. Chem. Phys. 113, 8918 (2000).