def __calculate_atoms_per_cm3(self, used_lock=False):
        """calculate for each element, the atoms per cm3"""
        stack = self.stack
        _density_lock = self.density_lock

        for _name_of_compound in stack.keys():
            if used_lock and _density_lock[_name_of_compound]:
                continue
            molar_mass_layer, atoms_per_cm3_layer = _utilities.get_atoms_per_cm3_of_layer(
                compound_dict=stack[_name_of_compound])
            # Update layer molar mass
            stack[_name_of_compound]['molar_mass'] = {'value': molar_mass_layer,
                                                      'units': 'g/mol'}
            # Update atoms per cm3
            stack[_name_of_compound]['atoms_per_cm3'] = atoms_per_cm3_layer
            for _index, _name_of_ele in enumerate(stack[_name_of_compound]['elements']):
                stack[_name_of_compound][_name_of_ele]['atoms_per_cm3'] = atoms_per_cm3_layer * \
                                                                          stack[_name_of_compound][
                                                                              'stoichiometric_ratio'][_index]
        self.stack = stack
calculate for each element, the atoms per cm3