Nonadiabatic hyperspherical approach to two-electron systems

Energy values for the ground and three lowest excited singlet S states of helium have been calculated using hyperspherical coordinates in a variational basis consisting of Sturmian functions in R, Legendre polynomials in θ₁₂, and problem-optimized functions in {α}. No adiabatic hypothesis is made. The convergence and energy values are superior to previous calculations using similar methods, but not as good as calculations in which r₁₂ is explicitly included. Plots of (H-E){Φ}(R,{α},θ₁₂) versus R and {α} are presented, and they show that the greatest departure from zero is in the {α}{}0 region.