Electron correlation in momentum space: the ground state of Li(2S)

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Abstract
Electron correlation is examined in momentum space for the individual intra- and inter-shell electron pairs in the ground state of Li(2S). It is established that the radial and angular components of the correlation have opposing influences on the inter-particle momentum distributions f(p12) and g(p12;p1), where p12= mod p1-p2 mod and p1= mod p1 mod . By examining the Coulomb shifts Delta f(p12) and, in particular, the partial Coulomb shifts Delta g(p12;P1) for each electron pair, such a feature enables one to identify the major component of correlation in different regions of momentum space. This represents a distinct advantage over the more traditional position space approach. For K alpha K beta , not only was it found that intra-shell correlation effects were influenced by the occupation of the 2s orbital but, more interestingly, the nature of the influence was seen to change markedly throughout different regions of space. For the K alpha L alpha and K beta L alpha inter-shells, the importance of angular correlation was highlighted and, for K alpha L alpha , the consequence of the Fermi effect was observed. Comparisons were made with a previous, and complementary, position-based study of Li(2S) and with the correlation effects found in momentum space for closed shell Li+(1S) and Be(1S).