The structure and the dynamics of the ordered solid phase of CBr4, a rigid molecule model

Abstract

Various known parameters of the atom–atom potential for the bromine atoms interaction have been used to model the experimental structure and the cohesive energy of the ordered phase II of CBr4. The set of parameters corresponding to krypton has turned out to give the best agreement with the experimental observations. The frequencies of the lattice vibrations at the zone center and the elastic constants have then been calculated and shown to be in a good quantitative agreement with the existing experimental data. The validity of the rigid molecule approach has been briefly discussed.

Revisiting the Disorder–Order Transition in 1-X-Adamantane Plastic Crystals: Rayleigh Wing, Boson Peak, and Lattice Phonons

“…Clark et al proposed a mechanism of transition from phase I to phase III via a formation of an intermediate semiordered phase on the basis of the values of the transition entropies. The XRD investigation confirms the existence of this semiordered phase as orthorhombic, space group Pmcn with four molecules per unit cell, showing orientational disorder but with different degrees of freedom compared to phases I and III.…”

Local order and orientational correlations in liquid and crystalline phases of carbon tetrabromide from neutron powder diffraction measurements

“…The ordered phase has been studied in relation to the order-disorder transition and in comparison with similar materials, using diraction methods 1,9,16,17 , measurements of thermodynamic parameters 18 and via molecular dynamics simulations 19 . The structure is a distorted face centered cubic one, which could eventually be rened as monoclinic 1 .…”

Crystal Structure

“…Most established force fields are parameterized using a combination of vibrational spectroscopy (mainly for bond length, bond angle, and torsion parameters [24,27,3 1,38]), elastic constants [39], thermodynamic data (mainly for non-bonded parameters via second virial coefficients, critical point data, diffusion coefficients [17]; heats of sublimation [15,18,40-421 (hydrocarbons) [29,38, (peptides, proteins, and nucleic acids) [39] (others); heats of formation [46,47] (hydrocarbons); heats of vaporization [3 I] (hydrocarbons); or heats of adsorption [48] (hydrocarbons on graphite)); and structural data (mainly for equilibrium 5 …”

“…bond length and bond angles as well non-bonded parameters, but also for torsion potentials) [24,28,30,39,47,, obtained via X-ray, electron or neutron scattering techniques (crystal structures of molecular compounds were used at an early stage to calibrate non-bonded potential parameters [15,18,[40][41][42]461 (hydrocarbons) [ 16,29,43- 451 (peptides and proteins)). Today's force field developers also rely strongly on quantum mechanical nb initio and semi-empirical calculations, which can be used to calculate all force field parameters for small molecules containing the fragments of interest (cf.…”