code: def plot_cv(self, tmin, tmax, ntemp, ylim=None, **kwargs):
          
          temperatures = np.linspace(tmin, tmax, ntemp)
  
          if self.structure:
              ylabel = r"$C_v$ (J/K/mol)"
          else:
              ylabel = r"$C_v$ (J/K/mol-c)"
  
          fig = self._plot_thermo(self.dos.cv, temperatures, ylabel=ylabel, ylim=ylim, **kwargs)
  
          return fig
docs: Plots the constant volume specific heat C_v in a temperature range.
  
          Args:
              tmin: minimum temperature
              tmax: maximum temperature
              ntemp: number of steps
              ylim: tuple specifying the y-axis limits.
              kwargs: kwargs passed to the matplotlib function 'plot'.
          Returns:
              matplotlib figure