  The charge density response function and the exchange hole are closely
related to each other via the fundamental fluctuation-dissipation theorem of
physics. A simple approximate model of the static response function is visually
compared on several examples in order to demonstrate this relationship. This
study is completed by illustrating the well-known isomorphism between the
exchange hole and the square of the dominant localized orbital lying in the
space region of the reference point of the exchange hole function. The
implications of these relationships for the interpretation of common chemical
concepts, such as delocalization, are discussed.
