Virial theorem and pressure calculations in the GGA

It is shown that using a generalized gradient approximation (GGA) functiona l describing exchange and correlation (xc) effects in electronic structure calculations implies additional re terms in the virial theorem and the pres sure tensor. These new expressions generalize the forms well known in the l ocal density approximation and are useful for checking the numerical precis ion of self-consistent field calculations for atoms and solids, and for acc urate pressure computations in heavy elements. Numerical examples are given .