Set displacemens

        Parameters
        ----------
        displacemens : array_like
            Atomic displacements of all atoms of all supercells.
            Only all displacements in each supercell case is supported.
            shape=(supercells, natom, 3), dtype='double', order='C'

def displacements(self, displacements):
        """Set displacemens

        Parameters
        ----------
        displacemens : array_like
            Atomic displacements of all atoms of all supercells.
            Only all displacements in each supercell case is supported.
            shape=(supercells, natom, 3), dtype='double', order='C'

        """

        disp = np.array(displacements, dtype='double', order='C')
        if (disp.ndim != 3 or
            disp.shape[1:] != (self._supercell.get_number_of_atoms(), 3)):
            raise RuntimeError("Array shape of displacements is incorrect.")

        if 'first_atoms' in self._displacement_dataset:
            raise RuntimeError("This displacement format is not supported.")

        self._displacement_dataset['displacements'] = disp