  A general formula for the orbital magnetic moment of interacting electrons in
solids is derived using the many-electron Green function method. The formula
factorizes into two parts, a part that contains the information about the
one-particle band structure of the system and a part that contains the effects
of exchange and correlations carried by the Green function. The derived formula
provides a convenient means of including the effects of exchange and
correlations beyond the commonly used local density approximation of density
functional theory.
