Knowledge Bank

Many-term valence-bond wave functions for the hydrogen molecule which used imaginary Slater-type orbitals (STO's) with principal quantum numbers on up to and including $n=6$ are described. These wave functions range from six to forty-two terms. The majority of the functions were optimized with respect to the orbital exponents and internuclear distance. The results show that for optimized orbital exponents a change in the principal quantum number of an STO of a given type, such as an np orbital, yields a very small change in that STO. It was found that wave functions using STO's with Slater exponents gave poor results because STO's with these exponents are much too diffuse. It was also found that regardless of the wave function in which a given term appeared, its value was nearly constant. The best energy obtained was ---1.1656 a.u. with the wave function using the 1s, $2p,3s,2p+,2p-$, and 3d STO's.