The chemical property of hardness is extremely important in the correct prediction of electron transfer between reacting chemical systems. Hardness is defined to be one-half the second derivative of the total energy of a chemical system with respect to the number of electrons. The requirement that the total energies of atom and pseudoatom match to second order with arbitrary changes in valence-state occupancy yields major decreases in the errors made when using pseudopotentials. The concept also clarifies the role of core density in pseudopotential application. A practical prescription is presented for generating such pseudopotentials and their corresponding core densities, and several ab initio results are compared with those of high-quality norm-conserving pseudopotentials. Significant improvements are found.

• Received 9 November 1992

DOI:https://doi.org/10.1103/PhysRevB.48.5031