Total-energy calculations using a gradient-expanded kinetic-energy functional

Using an approximate kinetic-energy functional, we have performed total-energy calculations on bulk and surface Si. The scheme is based on the Thomas--Fermi--von Weizs\"acker approximation of the kinetic-energy functional. The method is applied to the ground-state configuration of c-Si and H/Si(100) surfaces. The results are compared with those of experiments and detailed Kohn-Sham-Car-Parrinello type calculations. Encouraging agreement is found. We also compare our results with those obtained using the simpler Thomas-Fermi form of the kinetic-energy functional. In general, the von Weizs\"acker correction improves the results.