Electron Correlation in the (1s²2s)²S and (1s²2p)²P States of the Lithium Isoelectronic Sequence in Position and Momentum Space

In Part 1, the correlation problem is briefly reviewed and is followed by an outline of some approaches to electron correlation. In Part 2.1, correlation effects in the ground state of a series of open-shell systems in the form of Li-like ions are examined. The analysis is performed by using a partitioning technique which allows correlation effects in the individual electronic shells to be studied. These effects are examined by means of Coulomb holes, partial Coulomb holes, various correlation coefficients T and several one- and two-particle expectation values. The use of partial Coulomb holes illustrated changes in the relative importance of angular and radial correlation effects as the location of the test electron was varied. Comparisons are made between the K-shell results for the Li-like ions and those for the corresponding shell in some He- and Be-like ions. Similarly, the inter-shell results for Li are compared with their counterparts in both the Be atom and some excited states of He. In Part 2.2, the study of correlation effects is extended to an examination of the Li-like ions in the (1s²p)²P excited state. These results are compared with those for the ground state, discussed in Part 2.1. In the light of the results obtained in position space, a parallel investigation of the Li-like ions was carried out in momentum space and those results are presented in Part 3. In momentum space, the contrasting behaviour of the angular and radial components gave insight into the way electron correlation in the K-shell was influenced by the occupation of the L-shell. In addition, the analysis highlighted certain weaknesses in the description of the inter-shells in the excited state wavefunctions. The momentum results for the K-shell are compared for the ground and excited states of Li with Li+, Be²+ and also with the Be results.