A b i n i t i o and semiempirical SCF–MO computations for N+4; comparison of spin unrestricted and spin restricted methods

Abstract

Various basis sets (all but one minimal) were used in spin unrestricted ab initio SCF–MO computations on N+4. Computed values of the N+4 dissociation energy, D (N2−N+2), ranged from 49–72 kcal/mole for linear N+4 at a fixed internuclear separation R of 2.00 Å. Smaller dissociation energies were obtained by a spin restricted ab initio method in which the α- and β-spin eigenvector matrices were forced to be the same. All dissociation energies are larger than the experimental bond energy, but the smallest value was obtained with the extended basis set by the spin restricted ab initio method. There De(N2−N+2) was found to be 32.7 kcal/mole at Re=1.90 Å. Minimal basis set semiempirical computations were found to give results similar to those obtained by ab initio computations.