Function to create atomic lattice with n_atoms.

nx_atoms Integer, the length of lattice (in number of atoms).
ny_atoms Integer, the width of lattice (in number of atoms).
nz_atoms Integer, the depth of lattice (in number of atoms).
spacing The spacing between atoms in the lattice in Angstroms.
basis The basis in which to perform the calculation.
atom_type String, the atomic symbol of the element in the ring. this defaults to 'H' for Hydrogen.
charge An integer giving the total molecular charge. Defaults to 0.
filename An optional string to give a filename for the molecule.

molecule A an instance of the MolecularData class.

MolecularLatticeError If lattice specification is invalid.