The nudged elastic band (NEB) method is used for finding the transition state of a reaction or a diffusion event. The NEB method initially takes a guess at the configuration of several states that occur as the reaction proceeds. These states can often be obtained from linear interpolation between initial and final states. The NEB algorithm then converges these images onto the minimum energy path (MEP).
Theory
G. Mills, H. Jonsson and G. K. Schenter, Surface Science, 324, 305 (1995); H. Jonsson, G. Mills and K. W. Jacobsen, `Nudged Elastic Band Method for Finding Minimum Energy Paths of Transitions', in `Classical and Quantum Dynamics in Condensed Phase Simulations', ed. B. J. Berne, G. Ciccotti and D. F. Coker (World Scientific, 1998)
VASP
Nudged Elastic Band, VASP (http://cms.mpi.univie.ac.at/vasp/vasp/Elastic_band_method.html)
Nudged Elastic Band, Climbing Image(http://theory.cm.utexas.edu/vtsttools/neb.html)