QUANTUM-FIELD THEORETICAL METHODS IN CHEMICALLY BONDED SYSTEMS .5. POTENTIAL-ENERGY CURVES FOR N-2(X(1)SIGMA(G)(-]2N(S-4)()))

Many-body perturbation theory is applied to the nitrogen triple bond f or bond distances ranging from the atomic regime to about 0.6a(0) shor ter than equilibrium. A full-optimized reaction space model is used to compute orbital spaces with an even-tempered gaussian-type basis set and also with a nominal Bagus-Gilbert Slater-type basis set. Conservat ion of orbital angular momentum in the atomic regime leads to perturba tive theory for Hartree-Fock plus proper dissociation. Angular momentu m conservation can also be enforced with a scaled Slater-Condon parame ter. Third-order dissociation energies and spectroscopic constants app roach limits of the chosen basis sets. (C) 1993 John Wiley & Sons, Inc .