code: def _func(self, volume, params):
          
          e0, b0, b1, v0 = tuple(params)
          return (e0
                  + 9.0 / 8.0 * b0 * v0 * ((v0 / volume)**(2.0/3.0) - 1.0) ** 2
                  + 9.0 / 16.0 * b0 * v0 * (b1 - 4.) *
                  ((v0 / volume)**(2.0/3.0) - 1.0) ** 3)
docs: From Intermetallic compounds: Principles and Practice, Vol. I:
          Principles Chapter 9 pages 195-210 by M. Mehl. B. Klein,
          D. Papaconstantopoulos.
          case where n=0