Optimized norm-conserving pseudopotentials

The authors investigate the construction of norm-conserving 'soft-core' pseudopotentials with improved convergence properties of the plane-wave and perturbation expansions. The key factor is found to be the kinetic energy of the valence pseudo-orbitals. The total kinetic energy controls the convergence of the perturbation expansion of the total energy, the kinetic energy contained in the Fourier components beyond a certain cut-off limits the convergence of the plane-wave expansion. The simultaneous optimization of both expansions allows them to use the same pseudopotential in a rapidly convergent total-energy calculation for the crystalline phases, and in the calculation of interatomic forces to be used in atomistic simulations of the disordered phases.