Corrections to the beryllium ground-state energy

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Abstract
A relativistic coupled-cluster calculation including single and double excitations has been performed for the ground-state energy of beryllium. Comparison with corresponding nonrelativistic calculations shows the effect of relativity on the pair correlation which, together with the relativistic corrections to the Hartree-Fock energy, can be combined with the most accurate nonrelativistic ground-state energy available. Many-body radiative corrections were estimated by multiplying accurate results for hydrogenlike Be with the ratio between the Dirac-Hartree-Fock and hydrogenic electron densities at the nucleus. The energy associated with the motion of the nucleus with its finite mass can be deduced with sufficient accuracy from experiment. Subtraction of all these corrections from the experimental result leads to an ‘‘experimental nonrelativistic energy’’ of -14.667 353(2) hartrees.