Correlation Energy Calculation for the 1Σg+ Ground State of the Nitrogen Molecule

Abstract

Starting from a molecular Hartree—Fock wavefunction an extensive configuration-interaction calculation (201 configurations) has been carried out for the 1Σg+ ground state of N2. The matrix elements of the electrostatic Hamiltonian were calculated automatically. Both Brillouin—Wigner and Rayleigh—Schrödinger perturbation expansions, carried to a sufficient order, are shown to be good tools to find the lowest eigenvalue and eigenvector of very large matrices. Fifty percent of correlation energy is attained by this exact treatment. Since the second-order Rayleigh—Schrödinger perturbation expansions are a good approximation to the exact results, it supplies, in addition to a good test for the selecting of configurations, a practical means of evaluating pair correlations. By using this approximation and 3043 configurations, 66% of the correlation energy was found.

The calculation of the electric dipole moment of CO

“…The method of calculating the correlated wave function has already been discussed in detail for N, [9] so we need indicate only briefly what we have done here.…”

Exposé d'une méthode de détermination des orbitales virtuelles pour les interactions de configurations. Application à l'etat fondamental de l'atome de béryllium

“…L'utilisation des orbitales virtuelles correspondantes pour compltter la suite des orbitales ntcessaires n'est qu'une solution partielle au problkme (car il n'y a pas d'orbitales virtuelles pour les types de symttrie n'apparaissant pas dans la configuration primitive!) et ne permet en outre, le plus souvent, qu'un abaissement relativement lent de 1'Cnergie nkcessitant l'emploi d'un nombre ClevC de configurations [5]. Watson La (n + 1)-ikme orbitale &ant ainsi dtterminte, on rCpkte la m&me optration pour construire la (n + 2)-itme orbitale, la fonction de base B l'origine de la construction de la (n + 1)-ikme orbitale Ctant cependant tcartCe.…”