get_psp(self, sym=None, z=None)
get the pseudopotential filename from the psp database

:Parameters:

sym : string
the chemical symbol of the species

z : integer
the atomic number of the species


you can only specify sym or z. Returns the pseudopotential
filename, not the full path.

get_psp_nuclear_charge(self, psp)
get the nuclear charge of the atom from teh psp-file.

This is not the same as the atomic number, nor is it
necessarily the negative of the number of valence electrons,
since a psp may be an ion. this function is needed to compute
centers of ion charge for the dipole moment calculation.

We read in the valence ion configuration from the psp file and
add up the charges in each shell.

get_psp_valence(self, psp)
get the psp valence charge on an atom from the pspfile.