Interaction energy surfaces of small hydrocarbon molecules

Abstract

Nonbonding interactions of small alkane molecules were studied with ab initio methods. Previously reported energy data for ethane and propane dimers were supplemented with 1747 new configurations of dimers involving slightly larger hydrocarbons. The completed work provides interaction energy surfaces for all combinations of dimer pairs involving ethane, propane, isobutane, and neopentane and thus contains information of all chemical groups found in acyclic alkanes. The strongest attraction of the studied molecule pairs was encountered in isobutane C2h dimer, where an energy minimum of −1.784 kcal mol−1 at 4.28 Å separation of centermost carbon atoms was observed. The composite data set was fitted with a modified Morse pair potential energy function representing each interatomic C–C, C–H, and H–H interaction for easy transfer to molecular dynamics simulation programs. The new generic parameter set was shown to describe the ab initio data for these small alkane molecules with good accuracy. Qualitative comparisons with previously reported potential models were also made, and the relative capability of the models to reproduce quantum-chemical potential energy surfaces was investigated.