Correlated two-electron momentum properties for helium to neon atoms

Two-electron properties in momentum space for the atoms helium to neon have been calculated starting from explicitly correlated wave functions. The di fferent integrals involved in the calculation have been evaluated by using the Monte Carlo algorithm. In particular, the spherically averaged interele ctronic momentum distribution, gamma((2)) (p(12)), its radial moments [p(12 )(n)], with n=-2 to +3, the expectation value [p(1) . p(2)], and both the e lectron-electron coalescence, gamma((2))(0), and counterbalance, Gamma((2)) (0), densities have been calculated. A systematic study of the electronic c orrelation has been performed by comparing the correlated results with the corresponding Hartree-Fock ones. Finally an analysis of the structure of th e interelectronic momentum distribution in terms of its parallel and antipa rallel components has been carried out. (C) 1999 American Institute of Phys ics. [S0021-9606(99)30812-6].