A Lattice Dynamical Investigation of the Raman and the Infrared Wave Numbers of $MnWO_4$

A short-range force constant model has been applied using normal coordinate analysis to investigate the Raman and the infrared modes in multiferroic $MnWO_4$ having space group P2/c. The calculation of zone centre phonons has been made with eight stretching and seven bending force constants. The calculated Raman and infrared wave numbers are in good agreement with the observed ones. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wave numbers.