IMPORTANCE OF NONLINEAR CORE CORRECTIONS FOR DENSITY-FUNCTIONAL BASED PSEUDOPOTENTIAL CALCULATIONS

We have investigated the importance of nonlinear core corrections ~NLCC! for accurate density-functional based pseudopotential ~PSP! calculations. The quality of the PSP approach is assessed by comparing it to accurate all-electron calculations. It is found that a correct description of spin-polarized states requires the NLCC, even for first-row atoms. This is essential for simulations on magnetic systems and reaction processes that involve radicals. The NLCC is also essential for a realistic description of elements with more long-range core states such as alkali atoms. We propose a functional form for the partial NLCC, which is feasible in plane-wave calculations and suggest a scheme for choosing the default cutoff radius. @S0163-1829~99!02043-3#