Assessment of dynamical and nondynamical correlation energy components forthe beryllium-atom isoelectronic sequence

The partitioning of electron correlation energy into dynamical and nondynam ical components is examined in the context of the local- scaling transforma tion version of density- functional theory. An assessment is made of the re lative importance of these components for the beryllium atom and its isoele ctronic sequence. In particular, the problem of finding a multiconfiguratio n reference wave function differing only in dynamical correlation from the exact wave function is considered. It is shown that to a good approximation this reference wave function is given by Psi = C(1)1s(2)2s(2) + C(2)1s(2)2 p(2). The concepts of "long-range" and "short-range" correlation are re-exa mined from a perspective based on the reference wave function. (C) 1999 Ame rican Institute of Physics. [S0021-9606(99)30704- 2].