Vibrational frequency and LO-TO splitting determination for planar-zigzag β-poly(vinylidene fluoride) using density-functional theory

We have determined the vibrational frequencies for planar-zigzag β-poly(vinylidene fluoride) using first principles density-functional theory. Specifically, through the use of the generalized gradient approximation, periodic boundary conditions and the computation of longitudinal optical-transverse optical splittings (LO-TO splittings), we have found very good agreement between our vibrational frequencies and those found experimentally and by semi-empirical methods. We also find better agreement than a previous Hartree-Fock density functional determination. We have demonstrated the utility of our method for the accurate determination of vibrational frequencies for other novel ferroelectric co-polymers when experimental force constants may not be available.