Momentum space densities for the beryllium isoelectronic series

One- and two-body densities in momentum space have been calculated for the atomic beryllium isoelectronic series starting from explicitly correlated m ultideterminant wave functions. The effects of electronic correlations have been systematically studied by comparing the correlated results with the c orresponding Hartree-Fock ones. Some expectation values such as [delta>(*) over bar *((p) over right arrow)], [p(n)], [delta>(*) over bar *((p) over r ight arrow (12))], [p(12)(n)], [delta>(*) over bar *((P) over right arrow)] , and [P-n], where (p) over right arrow, (p) over right arrow (12), and (P) over right arrow stand for the electron-nucleus, interelectronic, and two- electron center-of-mass momentum coordinates, respectively, and the angular correlation coefficient have been obtained. All the calculations have been carried out by using the Monte Carlo algorithm. (C) 2000 American Institut e of Physics. [S0021-9606(00)31042-X].