TY - JOUR

T1 - Beryllium atom reinvestigated

T2 - A comparison between theory and experiment

AU - Mårtensson-Pendrill, Ann Marie

AU - Alexander, Steve A.

AU - Adamowicz, Ludwik

AU - Oliphant, Nevin

AU - Olsen, Jeppe

AU - Ster, Per

AU - Quiney, Harry M.

AU - Salomonson, Sten

AU - Sundholm, Dage

PY - 1991

Y1 - 1991

N2 - We compare the theoretical and experimental energies for the ground state of the beryllium atom and investigate possible sources for the small discrepancy of about 60 hartrees found by Bunge [Phys. Rev. A 14, 1965 (1976); 17, 486(E) (1978)]. Indications that the correlation energy may be underestimated in Bunges work have been confirmed by a recent, very extensive multiconfigurational Hartree-Fock (MCHF) calculation. We emphasize that the critical part of the comparison between theory and experiment is the sum of the first and second ionization energies the third and fourth are known more accurately from theory and present the theoretical results accordingly. Before a comparison with experimental results can be performed, corrections must be added to account for mass polarization, for the effect of relativity including the Breit interaction and for radiative effects. The previously unknown mass-polarization contribution to the first ionization energy has recently been determined experimentally. Relativity is most important for the 1s electrons and this effect was included in Bunges work, whereas the relativistic effect on the correlation involving the 2s electrons was neglected. Here, these contributions have been calculated to leading order. A crude estimate of the contribution to the Lamb shift from the 2s electrons is also given. When the revised relativistic corrections are combined with recent results from a very extensive MCHF calculation, the discrepancy in the beryllium ground-state energy is reduced to (1050) hartrees.

AB - We compare the theoretical and experimental energies for the ground state of the beryllium atom and investigate possible sources for the small discrepancy of about 60 hartrees found by Bunge [Phys. Rev. A 14, 1965 (1976); 17, 486(E) (1978)]. Indications that the correlation energy may be underestimated in Bunges work have been confirmed by a recent, very extensive multiconfigurational Hartree-Fock (MCHF) calculation. We emphasize that the critical part of the comparison between theory and experiment is the sum of the first and second ionization energies the third and fourth are known more accurately from theory and present the theoretical results accordingly. Before a comparison with experimental results can be performed, corrections must be added to account for mass polarization, for the effect of relativity including the Breit interaction and for radiative effects. The previously unknown mass-polarization contribution to the first ionization energy has recently been determined experimentally. Relativity is most important for the 1s electrons and this effect was included in Bunges work, whereas the relativistic effect on the correlation involving the 2s electrons was neglected. Here, these contributions have been calculated to leading order. A crude estimate of the contribution to the Lamb shift from the 2s electrons is also given. When the revised relativistic corrections are combined with recent results from a very extensive MCHF calculation, the discrepancy in the beryllium ground-state energy is reduced to (1050) hartrees.

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U2 - 10.1103/PhysRevA.43.3355

DO - 10.1103/PhysRevA.43.3355

M3 - Article

AN - SCOPUS:0001108392

SN - 1050-2947

VL - 43

SP - 3355

EP - 3364

JO - Physical Review A

JF - Physical Review A

IS - 7

ER -