Generated by Axel Kohlmeyer, starting from CAMPOS data:
http://www.physics.rutgers.edu/~dhv/uspp/uspp-cur/Work/038-Sr/038-Sr-gpw-nsp-campos/
adapted to PBE, with additional constraints to ensure that the amount of 
negative charge is negligibly small. This supersedes a previous potential
that had too large values of negative charge.