2(1)P 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 2(1)P state is computed from a 1200-ter m exponentially correlated Gaussian wavefunction with a Cartesian prefactor . New integrals necessary to evaluate matrix elements are presented. Test c alculations were performed on 2(1)P helium and 2(1)P lithium atoms yielding energies which are, respectively, 1 nanohartree and 0.35 microhartree in e rror. The upper bound to the energy of 2(1)P beryllium amounts to -14.47344 2016 hartree and the energy extrapolated to the basis set limit is -14.4734 58(5) hartree. The effect of the finite nuclear mass on the total and excit ation energies is also assessed. The predicted excitation energy is 0.19394 7(7) hartree (42566(2) cm(-1)) in perfect agreement with the experiment. (C ) 2001 Elsevier Science B.V. All rights reserved.