Accurate electron-pair, momentum-space properties for the helium atom

An explicitly correlated wave function, expanded in a basis set of 100 Gaussian geminals, is fully optimized for the ground state of the helium atom. The wave function is used to obtain a systematic set of intracular and extracular electron-pair properties in both position- and momentum-spaces. Comparison of the position-space properties with nearly exact values obtained from Hylleraas-type wave functions shows that the Gaussian geminal values are rather accurate. This lends credence to our claim that the momentum-space properties reported here are essentially definitive. Comparison is made with recent results obtained from multi-configuration Hartree-Fock calculations, and from Monte Carlo computations.