Computer simulation of the molecular dynamics of liquid dichloro methane

The molecular dynamics of CH₂Cl₂ in the liquid state have been simulated with two model representations of the intermolecular potential. These consist of a 3 × 3 and 5 × 5 atom-atom simulation with or without fractional charges at the atomic sites. A variety of thermodynamical and spectroscopic results show that the 5 × 5 potential is the more accurate. The effect of adding charges is significant but not pronounced. For example the simulated far infra-red spectrum looks 15% more like the real thing after an attempt has been made to include charge-charge electrodynamics. It is clear, however, that a better representation of the intermolecular pair potential of CH₂Cl₂ is needed to match the far infra-red results, and this can probably be obtained by measurements of the second $\text{dielectric}$ virial of CH₂Cl₂ over a sufficient temperature range. A coordinated experimental effort is needed to test the wide-range of simulated spectra now available for the asymmetric top CH₂Cl₂.