code: def set_xtal_info(self, space_group, unit_cell):
          
          self.space_group = space_group
          self.unit_cell = unit_cell
docs: Set the crystallographic information for the structure
          :param space_group: the space group name, e.g. "P 21 21 21"
          :param unit_cell: an array of length 6 with the unit cell parameters in order: a, b, c, alpha, beta, gamma