  Ab initio GW calculations are a standard method for computing the
spectroscopic properties of many materials. The most computationally expensive
part in conventional implementations of the method is the generation and
summation over the large number of empty orbitals required to converge the
electron self energy. We propose a scheme to reduce the summation over empty
states by the use of a modified static-remainder approximation, which is simple
to implement and yields accurate self energies for both bulk and molecular
systems requiring a small fraction of the typical number of empty orbitals.
