HARDNESS CONSERVATION AS A NEW TRANSFERABILITY CRITERION - APPLICATION TO FULLY NONLOCAL PSEUDOPOTENTIALS

The concept of chemical hardness has been recently adopted in the fram ework of Kohn-Sham theory as a faithful ab initio measure of pseudopot ential transferability. A fully self-consistent hardness theory was de veloped and employed to evaluate the transferability of semilocal pseu dopotentials. Hardness contains most of the relevant physical informat ion determining the transferability of pseudopotentials and is an impo rtant step forward with respect to the logarithmic derivative analysis . We discuss the main features of chemical hardness and the relations between chemical hardness and the original definitions of absolute and local hardness. We then apply the new criterion to investigate the tr ansferability of fully nonlocal Kleinman-Bylander pseudopotentials. Ha rdness conservation allows us to obtain a meaningful comparison betwee n them and the conventional norm-conserving ones and gives us a criter ion to improve the pseudopotential transferability of fully nonlocal p seudopotentials by suitably resetting their local part. (C) 1997 John Wiley & Sons, Inc.