Structural Properties and Dynamics of Thiophene in Sub/Supercritical Carbon Dioxide from Car–Parrinello Molecular Dynamics Simulations

Structrual and dynamic properties of thiophene (C4H4S) in supercritical carbon dioxide were studied using Car–Parrinello molecular dynamics simulations. The geometries and energies optimized for the thiophene–CO2 complex show a stable C–H···O hydrogen bond interactions both in gas phase and in supercritical CO2. The radial distribution functions of CO2 around thiophene in the supercritical phase state show a correlation suggesting C–H···O hydrogen bond and S···C interaction. Local structural properties of the mixtures were investigated by angular-radial distributions and spatial distribution functions. The results show a mutually parallel arrangement between the thiophene plane and CO2 molecules at short distances and a high probability of the thiophene being located in the radial directions of the CO2 molecules. The decay of orientational correlations at 318.15 K shows slower relaxation compared to those of 298.15 K for first and second rank correlations. The vibrations of CO2 and thiophene molecules have been examined through an analysis of the velocity autocorrelation functions of the atoms. The C–H stretching modes of thiophene in the isolated configuration are less red-shifted and have a much narrower frequency range than that in the mixtures.