Orbital Exponent Optimization in Elementary VB Calculations of the Chemical Bond in the Ground State of Simple Molecular Systems

Orbital exponent optimization in the elementary ab-initio VB calculation of the ground states of H[subscript 2][superscript +], H[subscript 2], He[subscript 2][superscript +], He[subscript 2] gives a fair description of the exchange-overlap component of the interatomic interaction that is important in the bond region. Correct bond lengths and about 85% of the experimental bond energies are obtained, giving a satisfactory first account of 1-electron (H[subscript 2][superscript +]), 2-electron (H[subscript 2]), 3-electron (He[subscript 2][superscript +]) chemical bonds and an adequate description of the corresponding Pauli repulsion in He+He. (Contains 1 figure, 6 tables and 2 notes.)