A set of rules put forward by the US physicist John Slater (1900–76) on an empirical basis; they describe the effect on any electron in a many-electron atom of the other electrons screening it from the full effect of the nuclear charge Z. Slater postulated that the effective charge Z_eff that any electron experiences is given by:

where s is a quantity called the screening constant. Subsequently, values of s were calculated using the Hartree–Fock procedure.