It would be better to provide atomic coordinates for bulk systems in Ang or AU instead of FRAC, since the atomic position tends to be translated in FRAC to keep the fractional coordinate within 0 to 1. The translation tends to generate a confusing movie in the visualization of the result.
Only three routines are added to implement the NEB functionality. They are neb.c, neb_run.c, and neb_check.c. The main routine is neb.c. It may be easy to implement related methods in neb.c.