The 2p² ³p state of some He-like systems : electron correlation effects
In Part I the nature of the electron correlation problem is briefly discussed and some approaches to its solution and analysis are described. In addition, some previous work concerning the 2p2 3P state of helium-like systems is reviewed. In Part II, position space electron correlation effects in the 2p2 3P state of H-, He, Li+ and Be++ are investigated. This study is conducted by examining the effects of correlation on a variety of radial, angular and interparticle distribution functions and expectation values. A number of different correlated and uncorrelated wavefunctions are employed for this purpose, allowing the merits of different approaches to be assessed. In particular, a natural orbital analysis performed on a configuration interaction wave- function is used to gauge the relative importance of the angular and radial components of correlation, which are found to act in unison. It is seen that the correlation effects are similar in kind to those found in the ground state systems, though they are of a greater magnitude in this doubly excited state. The variation of the correlation effects with the atomic number, Z, is also examined. To complement the results for position space, a parallel study of electron correlation effects in momentum space is presented in Part III. In contrast to the position space investigation, the radial and angular components of correlation are found to have opposing effects, producing a rich and informative total correlation effect. As in position space, the Z-dependent correlation behaviour is studied and it is seen to be more informative in momentum space. The correlation effects in momentum space are similar to the effects in ground state systems, but are of a greater magnitude. Some techniques used in this research are described in three appendices in Part IV.