calculate static pressure at 300 K.

        :param v: unit-cell volume in A^3
        :return: static pressure at t_ref (=300 K) in GPa

def cal_pst(self, v):
        """
        calculate static pressure at 300 K.

        :param v: unit-cell volume in A^3
        :return: static pressure at t_ref (=300 K) in GPa
        """
        params = self._set_params(self.params_st)
        return func_st[self.eqn_st](v, *params)