21P state of Be from exponentially correlated Gaussian functions

An accurate variational upper bound to the nonrelativistic clamped nucleus energy of the beryllium atom in the 21P state is computed from a 1200-term exponentially correlated Gaussian wavefunction with a Cartesian prefactor. New integrals necessary to evaluate matrix elements are presented. Test calculations were performed on 21P helium and 22P lithium atoms yielding energies which are, respectively, 1 nanohartree and 0.35 microhartree in error. The upper bound to the energy of 21P beryllium amounts to −14.473442016 hartree and the energy extrapolated to the basis set limit is −14.473458(5) hartree. The effect of the finite nuclear mass on the total and excitation energies is also assessed. The predicted excitation energy is 0.193947(7) hartree (42566(2) cm−1) in perfect agreement with the experiment.