Fit energies as function of volumes.

        Args:
            volumes (list/np.array)
            energies (list/np.array)

        Returns:
            EOSBase: EOSBase object

def fit(self, volumes, energies):
        """
        Fit energies as function of volumes.

        Args:
            volumes (list/np.array)
            energies (list/np.array)

        Returns:
            EOSBase: EOSBase object
        """
        eos_fit = self.model(np.array(volumes), np.array(energies))
        eos_fit.fit()
        return eos_fit