Density-Functional-Based Determination of Vibrational Polarizabilities in Molecules within the Double-Harmonic Approximation: Derivation and Application

We present a nonperturbative derivation for the primary contribution to the vibrational polarizability for molecules, clusters, and other finite systems. Using a double-harmonic approximation and a finite-field approach the vibrational polarizability is calculated within the generalized gradient approximation to the density functional theory for a variety of molecules and clusters. The agreement between theory and experiment is quite good. The results show that for small ionic molecules and clusters, inclusion of the vibrational polarizability is necessary to achieve agreement with experiment.