One- and two-body densities in position 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(r)>,
< r(n)>, <delta(r(12))>, < r(12)(n)>, <delta(R)>, and < R-n>, where r, r(1
2), and R stand for the electron-nucleus, interelectronic, and two electron
center of mass coordinates, respectively, have been obtained. All the calc
ulations have been carried out by using the Monte Carlo algorithm. (C) 1999
American Institute of Physics. [S0021-9606(99)30448-7].