[CP2K:6983] Re: Re-optimising transition state using dimer method

[luca]

Hi Tobias,
if you are confident for cutoff value try to decrease convergence
criteria for DM method.
Actually, MAXFORCE=8E4 for a transition state characterizzation is not
to high. Pay attention, DM uses CG algorithm, thus, the convergence is
very slow (hundred of iterations)!
L

On Thu, 2015-09-10 at 06:39 -0700, Tobias Kraemer wrote:
> Dear SL and Luca,
> 
> 
> I am aware of the numerical noise problem in vibrational analysis. I
> have worked on this issue for a while, in order to sort out a reliable
> protocol for my systems. 
> I have seen many examples where vibrational analysis yielded >50
> imaginary modes. Presently I am using EPS_SCF of 10E-6 in combination
> with MAX_FORCE 8E-4 for transition states, while the vibrational
> calculations uses a tighter EPS_SCF of 10E-8 in combination with DX
> 0.01. Optimising to minima a use somewhat tighter criteria than in the
> TS searches. I've come to realise that it is not easy to get good
> convergence in NEB calculations (don't ask me for the reason, it is my
> simple observation) and if the SCF convergence fails, it is impossible
> to converge to some decent structure in reasonable time. However, for
> a good number of optimisations (TS and minima) on the same system,
> this protocol has proven quite robust. I have heard from other people
> that they have experience similar issues with NEB, and I come to the
> conclusion that this is far from being straightforward. 
> 
> In view of my experience with the system so far, the presence of one
> small (~i25 cm-1) mode indicates that it is not numerical noise. I
> will try however to increase the cutoff (I am using 500 Ry indeed at
> the moment), to see if this changes anything. I have tested this in
> the past, and it did not influence the outcome of the result. Same for
> DX (increased to 0.02) So perhaps the answer lies in converging the
> dimer method to a tighter cutoff, in order to get the desired
> geometry. 
> 
> Best
> 
> Tobi
> 
> 
> 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
>         
>         
>         
>         
>         &MOTION
>           &GEO_OPT
>             TYPE TRANSITION_STATE
>              &TRANSITION_STATE
>                METHOD DIMER
>                 &DIMER
>                 &ROT_OPT
>                   OPTIMIZER CG
>                 &END ROT_OPT
>                &END DIMER
>              &END TRANSITION_STATE
>             OPTIMIZER CG
>             MAX_FORCE 8.0E-4
>             MAX_ITER 500
>           &END GEO_OPT
>           &PRINT
>              &TRAJECTORY
>               &EACH
>                  GEO_OPT 1
>               &END EACH
>             &END TRAJECTORY
>           &END
>         &END MOTION
>         
>         
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