The mass of each species of ion in the calculation may be specified in the cell file. The format for the BLOCK is
%BLOCK SPECIES_MASS units
%ENDBLOCK SPECIES_MASS
Each species is treated on a separate line. The first entry for species n is either the atomic symbol or the atomic
number and the second entry is the mass, which has default units of atomic mass units. If the mass of any species is
not specified then the default value of the mass will be assigned to that
species.