Comparative study of unconventional 1s basis functions for the 1Σ/sub g/+ ground state of H2 and He2++

We investigated various nonstandard 1s basis functions (generalized Slater--Gaussian, ellipsoidal Gaussian, floating spherical and ellipsoidal Gaussian, rational function, Hulthen approximation, two-Slater-type orbital, generalized Guillemin--Zener function, and various noninteger-n elliptical orbitals) for approximating the 1Σ+/sub g/ ground state of H2 and He2++. A CI trial wave-function including sigma/sub g/-type MO's is adopted and molecular integrals are evaluated numerically. The energy improvement on the 1s STO is small except for noninteger-n orbitals which closely approach the ''SCF limit''