NUCLEAR CUSPS IN THE HSF ELECTRON-DENSITY

The Hiller-Sucher-Feinberg (HSF) identity provides an alternative definition for the electron density. The behavior of the HSF electron density in the vicinity of nuclei is analyzed, It is shown that the HSF density possesses nuclear cusps at which its gradient is discontinuous. The discontinuities in the HSF density gradient satisfy a simple equation analogous to Kato's electron-nuclear cusp condition. However, in contrast to Kato's condition, the electron-nuclear cusp condition is satisfied by HSF densities originating from both exact and approximate electronic wavefunctions. Several numerical examples are presented to illustrate this property of the HSF electron density.