zero barrier from NEB calculations

Hi,

The barrier might be very small so that your second image is already on the
other side of the barrier.

If the computation cost is law you can increase the number of image until
you get a barrier.

The computationally most efficient way would be to use the free-end neb
with the last replica being the second replica of your previous complete
path. This way you will focus on the important part of your transition path.

Emile