Save matplotlib plot of the potential energy surface to a file.

        Args:
            filename: Filename to write to.
            img_format: Image format to use. Defaults to EPS.
            coords: internal coordinate name to use as abcissa.

def save_scan_plot(self, filename="scan.pdf",
                       img_format="pdf", coords=None):
        """
        Save matplotlib plot of the potential energy surface to a file.

        Args:
            filename: Filename to write to.
            img_format: Image format to use. Defaults to EPS.
            coords: internal coordinate name to use as abcissa.
        """
        plt = self.get_scan_plot(coords)
        plt.savefig(filename, format=img_format)