Volume-Dependent Atomic Polarizabilities for Vibrational Spectroscopy*

Vibrational spectroscopy methods, such as Raman and SFG, are valuable tools for characterizing the structure and dynamics of a wide range of systems. Computing spectra from MD simulations remains a signficant challenge, as accurate polarizabilities (α) are required for a large range of molecular configurations, and ab-initio α can be prohibitively expensive to compute for even small molecules. We extend the Thole model by making the initial atomic α functions of the interatomic distances, scaling them by the radius of the atom as defined by the volume the atom occupies in the molecule. This allows us to compute accurate α for molecules far from their equilibrium configuration. We then compute accurate Raman spectra of water and urea, and SFG spectra at the alumina-water interface.