Sets up a purely random structure with a given coordination.
        :param coordination: coordination number for the random structure

def setup_random_structure(self, coordination):
        """
        Sets up a purely random structure with a given coordination.
        :param coordination: coordination number for the random structure
        """
        aa = 0.4
        bb = -0.2
        coords = list()
        for ii in range(coordination + 1):
            coords.append(aa * np.random.random_sample(3, ) + bb)
        self.set_structure(
            lattice=np.array([[10, 0, 0], [0, 10, 0], [0, 0, 10]], np.float),
            species=["Si"] * (coordination + 1),
            coords=coords,
            coords_are_cartesian=False)
        self.setup_random_indices_local_geometry(coordination)