Rotational potential surface for alkanes: Basis set and electron correlation effects on the conformations of n-butane.

In this study, accurate molecular orbital calculations have been performed to characterize the structures and energies of the important stationary points on the rotational surface of n-butane. Complete geometry optimizations are performed to determine the structures of the two minima (trans and gauche) and the two transition states (C2 and C(2V)) at several theoretical levels. Basic set effects are investigated in a systematic manner by performing single point computations with several progressively larger basis sets (up to triple zeta plus polarization functions on all atoms).