code: def kunc_p(v, v0, k0, k0p, order=5):
      
      return cal_p_kunc(v, [v0, k0, k0p], order=order,
                        uncertainties=isuncertainties([v, v0, k0, k0p]))
docs: calculate Kunc EOS
      see Dorogokupets 2015 for detail
  
      :param v: unit-cell volume in A^3
      :param v0: unit-cell volume in A^3 at 1 bar
      :param k0: bulk modulus at reference conditions
      :param k0p: pressure derivative of bulk modulus at reference conditions
      :param order: order for the Kunc equation
      :return: pressure in GPa