A molecular dynamics study of liquid chloroform

Molecular Dynamics simulations of liquid chloroform with 200 molecules in the basic cube have been performed at 295 and 325 K. The interactions were described by a rigid five-site model with (12/6) Lennard-Jones spheres and partial charges at the atom positions. At room temperature four simulation runs have been carried out. Three of them differ in the method with which the Coulomb forces have been truncated at the cut off distance. For the fourth one the charges have been removed in order to study their influence on the MD results. The intermolecular structure functions have been calculated from the simulation and are found in good agreement with results from an x-ray measurement and with four out of five structure functions from neutron diffraction studies with isotopic substitution. Strong disagreement between simulation and experiment exists, however, for the six atom-atom radial distribution functions. The origin of this discrepancy is traced back to the difference in one of the five neutron structure functions (CH37Cl3); because of the consistency of the simulation results with each other and with the other experimental data, it can be attributed to uncertainties of the neutron scattering experiment. It is also shown that the expansion of the molecular pair correlation function in terms of spherical harmonics does not converge rapidly enough for the calculation of the first five so called g-coefficients with a sufficient degree of reliability from five neutron diffraction measurements. The self-diffusion coefficients have been calculated for 295 and 324 K, respectively, and found in good agreement with experimental results. Rotational diffusion coefficients, the spectral densities of hindered translations and of the librations are reported. Various reorientational correlation functions have been calculated, which reproduce satisfactorily the corresponding experimental results. The MD calculations show clearly that the description of the dielectric relaxation needs a multi-particle correlation function, whereas the far infrared absorption is due to single-particle motion.

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