Truncated pseudopotentials for alloy calculations

In first-principles plane-wave pseudopotential calculations, there is a subtle interplay between the convergence of the wave function and the pseudopotential expansions. Changing the cutoff of the plane-wave expansion often causes a change in the calculated physical quantities. We discuss the origin of this problem and how to ameliorate it by introducing a simple truncation of the pseudopotential in the reciprocal space. By exploiting the arbitrariness inherent in pseudopotentials, the method also provides an extra handle to "tune" the pseudopotentials to yield the best possible agreement with the all-electron results for bulk systems. We demonstrate the benefits of this truncation using Pd as an example and illustrate the results by calculations for some Pd-Al alloys. [S0163-1829(99)00836-X].