8Grains:
  N_constituents: 8
  mechanical:
    type: RGC
    D_alpha: [4.0e-06, 4.0e-06, 2.0e-06]
    a_g: [0.0, 0.0, 0.0]
    c_alpha: 2.0
    cluster_size: [2, 2, 2]
    output: [M, Delta_V, avg_dot_a, max_dot_a]
    xi_alpha: 10.0