One- and two-body densities for the beryllium isoelectronic series

One- and two-body densities in position space have been calculated for the atomic beryllium isoelectronic series starting from explicitly correlated multideterminant wave functions. The effects of electronic correlations have been systematically studied by comparing the correlated results with the corresponding 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(12), and R stand for the electron-nucleus, interelectronic, and two electron center of mass coordinates, respectively, have been obtained. All the calculations have been carried out by using the Monte Carlo algorithm. (C) 1999 American Institute of Physics. [S0021-9606(99)30448-7].