Ab initio studies on [bmim][PF6]-CO2 mixture and CO2 clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1, n -butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO 2 molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO 2 molecule are compared to find out that the CO 2 has specific interaction with a carbon atom present in the imidazolium ring. The CO 2 is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO 2 suggests that there is very good organization of CO 2 molecules around themselves even in the [bmim][PF 6 ]-CO 2 mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO 2 clusters reveals the greater tendency of the clusters with more CO 2 units, to deviate from the linear geometry.