code: def cal_panh(self, v, temp):
          
          if (self.eqn_anh is None) or (self.params_anh is None):
              return np.zeros_like(v)
          params = self._set_params(self.params_anh)
          return func_anh[self.eqn_anh](v, temp, *params,
                                        self.n, self.z, t_ref=self.t_ref,
                                        three_r=self.three_r)
docs: calculate pressure from anharmonic contributions
  
          :param v: unit-cell volume in A^3
          :param temp: temperature in K
          :return: pressure in GPa