Showing papers by "Roger Impey published in 1985"

Study of electron solvation in liquid ammonia using quantum path integral Monte Carlo calculations

Abstract: The solvation of an electron in liquid ammonia has been studied using quantum path integral Monte Carlo calculations. In agreement with previous experimental and theoretical deductions the charge distribution of the electron is compact. Various distribution functions characterizing the structure around the solvated electron are presented and the surrounding solvent structure is compared to that around a classical atomic anion. A qualitative discussion is given of the absorption spectrum based upon the form of the complex time dependence of the electron mean squared displacement correlation function.

Structural and dynamic properties of lithium sulphate in its solid electrolyte form

Abstract: The properties of solid lithium sulphate have been studied by computer simulation. At sufficiently high temperatures, the simulated crystal behaves as a solid electrolyte with lithium ion (jump) diffusion and sulphate group rotation. The atomic radial distribution functions in the rotator phase are discussed in relation to the low temperature, fully ordered, monoclinic structure and the nature of the orientational disorder of the sulphate groups is characterized in terms of tetrahedral rotor functions. The crystal structure factor is found to be sensitive to the model adopted for the charge distribution of the anions; good agreement with experimental neutron diffraction data is obtained when a charge distribution consistent with ab initio quantum mechanical calculations is used. The phase transition whereby the low temperature monoclinic structure transforms to the disordered cubic phase has been investigated by the constant pressure molecular dynamics method. The nature of the lithium ion diffusive motion and its coupling to the anion reorientation, the relaxation of the orientational order and the lattice vibrations are all briefly discussed.

Simulation of the cubic to orthorhombic phase transition in potassium cyanide

Abstract: Constant pressure (NPH) ensemble molecular dynamics calculations have been used to study the cubic to orthorhombic phase transition that occurs upon cooling potassium cyanide at low pressures. A rigid ion model consisting of interionic electrostatic terms plus nonbonded atom–atom interactions has been found to yield an almost quantitative account of the transition. In particular, the extreme softening of the shear elastic constant C44 and the anomalous dispersion of the transverse acoustic phonons propagating along the crystal [100] direction in the cubic phase are well reproduced.