[CP2K:6980] Re: Re-optimising transition state using dimer method

S Ling lingsa... at gmail.com
Thu Sep 10 12:46:30 UTC 2015

Hi Tobias,

One thing you need to keep in mind is that in CP2K, the vibrational modes
are calculated numerically, i.e. they will be sensitive to the DX value you
specified in your &VIBRATIONAL_ANALYSIS section. You will also need to use
extremely tight energy and force convergence criteria to obtain a very good
geometry for the VIBRATIONAL_ANALYSIS calculation.


On 10 September 2015 at 12:46, Tobias Kraemer <161brun... at gmail.com>

> Hello,
> 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)
> Tobias
> 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
>>        METHOD DIMER
>>         &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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