Accurate structure factors from pseudopotential methods

Highly accurate experimental structure factors of silicon are available in the literature, and these provide the ideal test for any ab initio method for the construction of the all-electron charge density. In a recent paper [J. R. Trail and D. M. Bird, preceding paper, Phys. Rev. B 60, 7875 (1999)] a method has been developed for obtaining an accurate all-electron charge density from a first-principles pseudopotential calculation by reconstructing the core region of an atom of choice. Here this method is applied to bulk silicon, and structure factors are derived and compared with experimental and full-potential linear augmented plane-wave (FLAPW) results. We also compare with the result of assuming the core region is spherically symmetric, and with the result of constructing a charge density from the pseudo-valence-density plus frozen-core electrons. Neither of these approximations provide accurate charge densities. The aspherical reconstruction is found to be as accurate as FLAPW results, and reproduces the residual error between the FLAPW and experimental results.