Re-optimising transition state using dimer method

Tobias Kraemer 161brun... at
Thu Sep 10 11:46:18 UTC 2015


I have tried out your suggestions regarding the dimer method, and in 
principle I have now successfully run this calculation. Unfortunately I 
didn't get the desired result, i.e. I didn't eliminate the spurious 
imagianary mode in the ts structure. What surprises me is the fact that 
there are hardly any noticable changes in the geometry. Changes affect the 
3. and 4. decimal place of bond distances and angles (negliglible). What I 
expected to see are somewhat more noticable movements in those parts of the 
molecule which correspond to the small imaginary mode and should refine to 
a minimum (say small rotations of certain groups or other soft modes). This 
hasn't happened apparently, and hence the new structure is almost identical 
to the input structure, and hence - unsurprisingly - yields the same 
undesired imaginary modes again. I want to point out that this spurious 
mode is around 25 cm-1, a very soft mode, but it must be possible to get 
rid of it (and in fact, the constrained optimisation which I have used in 
another but related example did exaclty this). Could you advice me here in 
terms of parameters I should change. I have played around with the angle 
tolerance parameter, what about DR? Shoud I use tighter geometry 
convergence? At the moment I am more worried about the fatc that there is 
hardly any change in the geometry during the dimer optimisation. What 
protocols do you normally employ when you optimise to a saddle point of 
higher order? How do you refine the TS?

Thanks for your help (inputs plut other files attached)




On Tuesday, September 1, 2015 at 5:11:13 PM UTC+1, Tobias Kraemer wrote:
> Hi all,
> I am trying to re-optimise a transition state structure which has a 
> spurious (small) imaginary mode on top of the large imaginary mode which 
> corresponds to the transition state. I've also tested doing a constrained 
> optimisation fixing selected atoms involved in the transition state, which 
> also worked in this particular case. Howeve, I would also like to try our 
> the dimer method for the purpose of re-optimising a transition state 
> structure. To this end, I have composed an input, however, the job crashes 
> and I keep getting an error message about certain line Search type not 
> being implemented (looks quite obvious from the message). However, I can't 
> seem to find what I need to change to make it work. Your advice would be 
> much appreciated. The motion section can be found below, full input file 
> also uploaded. 
> Any ideas on how to correctly set up a calculation using the dimer method 
> are welcome
> Thanks for your help
> Tobias
>  ************************************************************************
>  *** 16:48:48 ERRORL2 in cg_utils:cg_linmin processor 0  :: err=-1000 ***
>  *** UNIMPLEMENTED, Line Search type not yet implemented in CG for TS ***
>  *** search.                                                          ***
>  ************************************************************************
>  ===== Routine Calling Stack =====
>            10 cg_linmin
>             9 cp_cg_main
>             8 geoopt_cg
>             7 cp_rot_opt
>             6 cp_eval_at_ts
>             5 cp_eval_at
>             4 cp_cg_main
>             3 geoopt_cg
>             2 cp_geo_opt
>             1 CP2K
>   &GEO_OPT
>         &DIMER
>         &ROT_OPT
>           OPTIMIZER CG
>         &END ROT_OPT
>        &END DIMER
>     MAX_FORCE 8.0E-4
>     MAX_ITER 500
>   &PRINT
>       &EACH
>          GEO_OPT 1
>       &END EACH
>   &END
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