Electron correlation in momentum space: The beryllium-atom isoelectronic sequence

Abstract

Various momentum-space properties are computed for the Be atom and its isoelectronic sequence from highly accurate configuration-interaction wave functions that include more than 90% of the correlation energy. We assess the effects of electron correlation in momentum space by making a comparison with the results obtained from the Hartree-Fock level. The results reveal differences that indicate that the inclusion of electron correlation is necessary if one is to obtain highly accurate momentum space quantities. Additionally, our results show that the sum of the position and momentum-space entropies increases in going from the Hartree-Fock to the configuration-interaction level, supporting the argument that this sum may be used in assessing the quality of a basis set. The observation that the entropy sum and the other calculated properties remain stable with the inclusion of more electron correlation suggests that these properties are not sensitive to the amount of electron correlation and that density convergence criteria may be more useful in obtaining an accurate electronic distribution than criteria based solely on the amount of correlation energy.