The repetition score is a measure for how many of the atoms in the electrode candidate can be repeated beyond the electrode extension in the central region by translating them by a multiple of the electrode length, minus the number of atoms in the electrode candidate itself.

As an example: If we have 8 atoms in the electrode candidate, and we find 2 complete

repetitions of these atoms beyond the electrode extension (translating them by 1*electrode_length, and by 2*electrode_length)

then the score for this candidate would be 8.

If we find exactly one complete repetition, the score would be zero.

If only 4 of the 8 atoms are repeated, the score would be -4.

So, a negative score can still mean that the electrode candidate is suitable, but it is not always guaranteed.

Note that, all this applies to "full" (i.e. not minimal) electrodes.