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].