Nonrelativistic energy levels of the helium atom

Abstract

The nonrelativistic energy levels of a helium atom are calculated for S , P , D and F states. The calculations are based on the variational method of "exponential" expansion. The convergence of the calculated energy levels is studied as a function of the number of basis functions N . This allows us to claim that the obtained energy values (including the values for the states with a nonzero angular momentum) are accurate up to 28-35 significant digits.