Lattice dynamics of crystalline carbon disulphide—revisited

Abstract

The lattice dynamics of CS2, assuming it to behave as a molecular crystal, is reexamined in the light of (a) accurate new lattice parameter values and (b) a recent molecular dynamics model for the liquid. Quadrupole interactions of the magnitude indicated by various workers are found to have negligible effect. This molecular dynamics model and a range of other simple, rigid molecule, atom-atom interaction models tailored to reproduce observed crystalline properties are found to be unable to simulate such properties unless molecular inclinations are changed by a common amount which is well outside experimental uncertainty, or abnormally large quadrupole moments are assumed. Details of the assumed potential functions of models with similar predictive powers are found to vary in a surprising manner.

Calculation of crystal and molecular structures of carbon disulfide CS2

“…[30][31][32][33][34][35][36][37][38] They use intermolecular potential of Buckingham type ͑exp Ϫ6 Ϫ1͒, with or without inclusion of Coulombic interactions, and several approximations, among which the most obvious one is the disregard of temperature effects. To our knowledge, only Impey and Klein, with their NMD technique, try but do not succeed in reproducing the experimental variation of the lattice parameter c of CS 2 structure, with temperature.…”

“…These effects were neglected in previous crystal structure and lattice dynamics calculations without thermal effects and using the rigid molecule approximation. [30][31][32][33][34][35][36][37] However it was suggested experimentally that CS 2 is a flexible molecule. 38 Even the new molecular dynamics ͑NMD͒ technique does not succeed in reproducing the experimental variation of the lattice parameter c of CS 2 structure with temperature.…”

Dynamical Model for the Lattice Frequencies and Crystal Field Splittings of Carbon Disulphide

“…I n general, there have been problems in simultaneously satisfying the equilibrium and energy of the crystal and obtaining a good fit to the experimental frequencies. For example, Grout and Leech [12] found it necessary to change the orientation of the molecules from that determined experimentally in order to obtain equilibrium and to increase the value of the molecular quadrupole moment beyond that determined by independent measurements or calculations, in order t o match the frequencies. On the other hand, Burgos and Righini [la] used anisotropic atom-atom interactions in order to avoid these difficulties.…”