code: def save_plot(self, filename, img_format="eps", ylim=None, units="thz"):
          
          plt = self.get_plot(ylim=ylim, units=units)
          plt.savefig(filename, format=img_format)
          plt.close()
docs: Save matplotlib plot to a file.
  
          Args:
              filename: Filename to write to.
              img_format: Image format to use. Defaults to EPS.
              ylim: Specifies the y-axis limits.
              units: units for the frequencies. Accepted values thz, ev, mev, ha, cm-1, cm^-1.