  The charge and entropy currents across a quantum point contact is expanded as
a series in powers of the applied bias voltage and the temperature difference.
After that, the expansions of the Seebeck voltage in temperature difference and
the Peltier heat in current are obtained. With a suitable choice of the average
temperature and chemical potential, the lowest order nonlinear term in both
cases appear to be of third order. The behavior of the third-order coefficients
in both cases are then investigated for different contact parameters.
