Comparison of Standard and Modified Orthogonalized Plane-Wave Methods

We compute electron energy levels for some selected irreducible representations of two crystals, Cu and La${\mathrm{Sn}}_3$, using both the standard orthogonalized plane-wave method (OPW) and a modified form of this method (MOPW). It is shown that (for a nonrelativistic nonself-consistent treatment, at least) the convergence, in the sense of the number of symmetrized plane waves required, is both more rapid and more reliable for MOPW than for OPW. For the two crystals chosen, standard OPW was found to be reasonably good for La${\mathrm{Sn}}_3$ but inadequate for Cu, whereas MOPW was quite adequate for both.