Assuming your initial and final structures are well optimized, I would lower the spring constant by half, as 0.1 is perhaps too high, which may cause excessive rigidity, triggering the error.

Rgds,

Gabriel Vinicius

Thanks for your reply, Gabriel Vinicius .

Unfortunately, NEB still doesn't work when reducing the spring constant. I have tried both 0.05 and 0.01, with no avail. I obtained both reactant and product geometries with a CASTEP geometry optimization, I hope they are well optimized.

Gotcha! Well, I'm not familiar with CASTEP's tags and can't really advise you further. I would try this calc using QE instead if I were you. It's like open-source, has more online resources, and a larger community to help.

Good luck, Pablo García-Aznar

Cheers

I haven't encountered this error, but I don't use the transition state search functionality very much. Are you running this via Materials Studio or directly on the command-line? Would you mind sharing your input files with me and I can take a look?

In general, I'd recommend asking specific questions like this on the CASTEP community list. Like Gabriel said for QE, it's worth asking the larger user community in cases like this:

https://www.jiscmail.ac.uk/lists/CASTEP.html

this is one of the advantages of us making CASTEP's source code available for free, lots of people can help!

Thanks for your reply, Philip James Hasnip.

I am running standalone CASTEP, academic license, version 23.1 .

Sure, I attach the input .param file.

For the .cell file, it contains %BLOCK LATTICE_CART, %BLOCK CELL_CONSTRAINTS (all fixed, so 0), POSITIONS_FRAC of reactants, intermediate and product, FIX_COM : false and kpoint_mp_grid : 1 1 1

What could be the problem?

Many thanks for your help!