[CP2K-user] [CP2K:20756] Inconsistent geometry optimisations

['daniel Storm' via cp2k]

Hi everyone,

Just to provide some context, in our group we use CP2k to model molecular 
reactivity in the solid state, so slightly different than “standard” solid 
state chemistry. We run optimisations for minima and transition states 
(TS), whose character we confirm by running phonon calculations.

Now, to the issue. I am working with a crystal structure of an iridium 
organometallic salt, [Ir(PONOP)(H)Me][BArF4], however, I am encountering 
issues with achieving consistent optimisations. Despite starting from the 
same experimental structure, I am getting very different SCF energies (up 
to 3 kcal/mol) and I have observed minor differences in the resulting 
geometries. I think that those geometries are close enough to not show that 
big of an SCF difference, but my main worry is the fact that the starting 
point is always the same.

The convergence criteria that I am currently using is MAX_FORCE 1.0 x 10-4. 
I have attempted to improve this by tightening the criteria (MAX_FORCE, 
MAX_DR, RMS_DR and RMS_FORCE) to 1.0 x 10-6, but this didn’t fix the issue. 
All the optimisations are done with the PBE-D3 functional and 
DZVP-MOLOPT-SR-GTH basis set.

So, to sum up, I run optimisations with the same starting geometry that 
converge to different structures, and I am not sure why or which criterion 
to use to select one structure over the other, etc. 

I have worked with other organometallic salts in the past, and this is the 
first time I find this issue. I am using CP2k version 2023.2 in the HPC 
cluster Archer-2.

Has anyone seen this before? Any advice on how to proceed?

Thanks in advance,

Daniel.

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