PSEUDOPOTENTIALS WITH POSITION-DEPENDENT ELECTRON MASSES

Many of the computational limitations of the Green's-function quantum Monte Carlo (GFQMC) method could be overcome by using pseudopotentials. However, standard norm-conserving pseudo-potentials are unsuitable because they contain nonlocal angular-momentum projection operators. This prompted Bachelet, Ceperley, and Chiocchetti (BCC) to put forward a new class of pseudopotential specifically for use in GFQMC calculations. The BCC pseudo-Hamiltonian does not involve any nonlocal integral operators, but consists of a local potential and a kinetic-energy term with a position-dependent electron effective-mass tensor. We find that sensible BCC pseudopotentials exist only when the atomic valence eigenvalues increase with increasing angular momentum, and even when this condition is met it can be difficult to ensure the correct scattering properties in more than two angular-momentum channels. Nevertheless, we have constructed good BCC pseudopotentials for a wide selection of atoms and have done density-functional calculations in atoms and solids to test their transferability. It turns out that the transferability depends very much on the method used to construct the pseudopotentials (different methods can lead to very different pseudopotentials with very different transferabilities) but can be comparable to that of ordinary nonlocal pseudopotentials in some cases.