message: Added ensuring that only unique numbers in the given atomic numbers are used in MBTR.
diff: @@ -60,7 +60,8 @@ class MBTR(Descriptor):
  system, but should contain all the elements that are ever going
  to be encountered when creating the descriptors for a set of
  systems. Keeping the number of handled elements as low as
  - possible is preferable.
  + possible is preferable, especially if a dense representation
  + (e.g. numpy array) is needed as an output.
  k (set or list): The interaction terms to consider from 1 to 3. The
  size of the final output and the time taken in creating this
  descriptor is exponentially dependent on this value.
  @@ -140,7 +141,7 @@ class MBTR(Descriptor):
  super().__init__(flatten)
  self.system = None
  self.k = k
  - self.atomic_numbers = atomic_numbers
  + self.atomic_numbers = list(set(atomic_numbers)) # The given atomic numbers are first made into a set to remove duplicates, and then made into list for enabling ordering.
  self.grid = grid
  self.weighting = weighting
  self.periodic = periodic
  