message: Fix small error in k2 term normalization
diff: @@ -949,9 +949,9 @@ class MBTR(Descriptor):
  amounts[index] = list(S.get_atomic_numbers()).count(number)
  y = gaussian_sum
  if i==j:
  - NANB = amounts[i] * amounts[j]
  - else:
  NANB = 0.5 * amounts[i] * amounts[j]
  + else:
  + NANB = amounts[i] * amounts[j]
  y_normed = (y * V) / (NANB*4*np.pi)
  if self.flatten:
  k2[start:end] = y_normed
  