def plot(self, thin_number=10, volume_temp_exp=None):
        """Plot three figures.

        - Helmholtz free energy at volumes and temperatures.
        - Equilibrium volumes at temperatures.
        - Thermal expansion coefficients at temperatures.

        """
        import matplotlib.pyplot as plt

        plt.rcParams["pdf.fonttype"] = 42
        plt.rcParams["font.family"] = "serif"

        fig, axs = plt.subplots(1, 3, figsize=(7, 3.5))
        axs[0].xaxis.set_ticks_position("both")
        axs[0].yaxis.set_ticks_position("both")
        axs[0].xaxis.set_tick_params(which="both", direction="in")
        axs[0].yaxis.set_tick_params(which="both", direction="in")
        self._plot_helmholtz_volume(axs[0], thin_number=thin_number)
        axs[1].xaxis.set_ticks_position("both")
        axs[1].yaxis.set_ticks_position("both")
        axs[1].xaxis.set_tick_params(which="both", direction="in")
        axs[1].yaxis.set_tick_params(which="both", direction="in")
        self._plot_volume_temperature(axs[1], exp_data=volume_temp_exp)
        axs[2].xaxis.set_ticks_position("both")
        axs[2].yaxis.set_ticks_position("both")
        axs[2].xaxis.set_tick_params(which="both", direction="in")
        axs[2].yaxis.set_tick_params(which="both", direction="in")
        self._plot_thermal_expansion(axs[2])
        plt.tight_layout()
        return plt