Given fractional coordinates in the lattice basis, returns corresponding
        fractional coordinates in the lll basis.

def get_lll_frac_coords(self, frac_coords: Vector3Like) -> np.ndarray:
        """
        Given fractional coordinates in the lattice basis, returns corresponding
        fractional coordinates in the lll basis.
        """
        return dot(frac_coords, self.lll_inverse)