During a TS search, freeze the catalyst or not ?

[jianmin]

Dear all and especially Prof. Graeme,

Attached is the ball-and stick structure of a homogeneous catalyst monomer that I am working on. The atom at the center and in dark yellow is iron (Fe), linking to two ligands.

I was trying to search the transition state (TS) of dihydrogen molecule splitting (H2 -> H + H) on the Fe atom of the monomer by the dimer method. During the TS search, I have of course allowed H2 or two H atoms to relax; also, I have allowed all atoms of the catalyst monomer to move, in which a lot of degrees of freedom are on the run. But the VASP job by the dimer method failed to find a meaningful TS.

Does it indicate that I should fix all atoms of the catalyst monomer and only allow the two H atoms to move ? Is it valid ?

[graeme]

It sounds like you know both the initial and final states of your reaction of interest. I suggest using an NEB calculation to find the saddle point that connects them.

[jianmin]

Prof. Graeme, thanks for the heads-up. I will run the NEB method first.