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I'm doing Nudged elastic band calculations using VASP TST tools to calculate the diffusion energy barriers in the Ni system (with a vacancy and a Re atom as the solute).

Now, in the elastic band method, the endpoints, ie , the first and the last images are kept fixed. So, instead of using unrelaxed POSCAR files, I run VASP calculations for the endpoints to get the relaxed structure (ISIF =3) and then use the obtained CONTCAR file as the POSCAR in the NEB calculations.

The calculations worked fine for the simple solute-vacancy exchange, but for solvent-vacancy exchanges with a solute atom lying nearby (in order to calculate the correlation factors), the calculations are not going beyond the 1st ionic step and I?m getting the following in the output file:-

?VERY BAD NEWS! internal error in subroutine IBZKPT:
Reciprocal lattice and k-lattice belong to different class of lattices. Often results are still useful... 168?

I'm using a 3x3x3 atom supercell and gamma centred 5x5x5 k-points.
I haven't tweaked the ISYM or the SYMPREC tags in the INCAR file.

Where is the problem?

NEB only runs for cells which the SAME lattice parameters (constant volume and cell-shape) for initial and final states, therefore ISIF=3 is not appropriate to determine the geometries of the initial and final states.