code: def cal_pst(self, v):
          
          p_h = self._hugoniot_p(v)
          p_th_h = self._hugoniot_pth(v)
          p_st = p_h - p_th_h
          return p_st
docs: calculate static pressure at 300 K.
  
          :param v: unit-cell volume in A^3
          :return: static pressure at t_ref (=300 K) in GPa