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.