Ab initio studies on [bmim][PF sub(6)]-CO sub(2) mixture and CO sub(2) clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF sub(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 sub(2) molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO sub(2) molecule are compared to find out that the CO sub(2) has specific interaction with a carbon atom present in the imidazolium ring. The CO sub(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 sub(2) suggests that there is very good organization of CO sub(2) molecules around themselves even in the [bmim][PF sub(6)]-CO sub(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 sub(2) clusters reveals the greater tendency of the clusters with more CO sub(2) units, to deviate from the linear geometry.