Ab-initio total energy studies of the static and dynamical properties of ice Ih

We present a detailed study of the structural and dynamical properties of ice lh. Methods used include the ab-initio pseudopotential and molecular orbital techniques. In order to simulate the proton disorder present in ice Ih supercells are constructed with the orientation of water molecules determined in such a way that all possible nearest neighbor orientations are included while still obeying the Bernal-Fowler ice rules. For structures considered all structural parameters are relaxed. The dependence of bond length on the orientation of surrounding molecules in both the dimer and fully coordinated system is discussed. All local dimer orientations are accounted for in the supercell of ice Ih considered. The dynamical properties of a 16-molecule supercell model of ice Ih are then investigated via direct determination of the zone center dynamical matrix. Here the dynamical matrix is calculated directly from atomic forces obtained when each atom is shifted away from its equilibrium position. The vibrational modes are then calculated, and the mode frequency as a function of microscopic deformation is discussed.