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A nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex potential energy landscape, using either quantum electronic-structure or classical atomic potential methods. The Fortran module “NEB” contained in the downloadable file “neb.F” implements our C2-NEB algorithm. Our more stable and reliable C2-NEB code is modified from the single climbing image (C1-NEB) open-source code authored by G. Henkelman (U. Texas - Austin). C2-NEB code is implemented to replace NEB subroutine in the VASP plane-wave electronic-structure code (available at


If you utilize the code, please cite the following papers: [1] Method and [2] First Application.

[1] N. A. Zarkevich and D. D. Johnson, J. Chem. Phys. 142, 024106 (2015). doi: 10.1063/1.4905209;
[2] N. A. Zarkevich and D. D. Johnson, Phys. Rev. Lett. 113, 265701 (2014). doi: 10.1103/PhysRevLett.113.265701.

Affiliations: Zarkevich, Ames Laboratory; Johnson, Ames Laboratory, Materials Science and Engineering