DENSITY-FUNCTIONAL EXCHANGE IDENTITY FROM COORDINATE SCALING

A density-functional exchange identity is derived in a very simple man ner through coordinate scaling for the external potential within the c oupling-constant approach. It is observed that this identity may be ex pressed as a recursion relation which is especially useful for testing approximations to the exchange functional, and to its corresponding e xchange potential, as part of a full density-functional calculation in volving correlation as well as exchange.