Similarity analysis of the conformational potential energy surface of n-pentane

Wave-function-based ab initio (Møller–Plesset perturbation theory and Hartree–Fock SCF), tight-binding (SEOEM), semiempirical (MNDO, AM1, and PM3) and density functional (B3LYP) quantum chemical methods have been applied to the generation of the full conformational potential energy surface of n-pentane. All the critical points (local minima, first-order saddle points, and local maxima) have been localized in each case. Their numbers, 11, 20, and 9, respectively, are precisely in accordance with the topological theory of periodic functions. There are fourteen unique critical points on the conformational potential energy surface of n-pentane. tive similarity indices computed for pairs of conformational potential energy surfaces have revealed that of the generated surfaces the SEOEM one is the most similar to that obtained at the Møller–Plesset level of theory. Surprisingly, the highest similarity index has been obtained for the pair of the Hartree–Fock and B3LYP surfaces.