The file IBZKPT is compatible with the KPOINTS file and is generated if the automatic k-mesh generation is selected in the file KPOINTS. It contains the k-point coordinates and weights (and if the tetrahedron method was selected additional tetrahedron connection tables) in the 'Entering all k-points explicitly' format used for providing k-points 'by hand'. This file can also be generated with the external tool:
> kpointsIBZKPT may be copied to the file KPOINTS to save time, if one KPOINTS set is used several times.