[ase-users] Optimization - fmax in NEB

[Jens Jørgen Mortensen]

Den 31-03-2013 17:21, Sungsik Kim skrev:
> Hello,
> This is Sungsik.
> Thank you for your help last time. I got correct NEB images now.
> I have a question about fmax in optimaztion.
> I need activation barrier for dissociative adsorption of methane on 
> platinum.
> I already get surface potential energy with fmax 0.05 which is default 
> by DACAPO.
> However, in getting the activation barrier with DACAPO calculator with 
> fmax=0.05,
> Calculation has not been completed even though I run it over 10days.
> And my computer looks like being exploded after 30000th calculation.
> I ran it by NEB with EMT calculator with different fmax in NEB code.
> Even though surface potential energy is a little different, but I got 
> the same activation
> energy in different fmax value such as 0.5 , 0.1, and 0.05 in optimize 
> in NEB.
> It is okay to use fmax value. 0.5 in optimazation in NEB to get 
> activation barrier ?
> I would like to know if this affects activation barrier too much?

I think one can often get away with quite large fmax, but it will depend 
on the reaction so you will have to do some tests yourself. What do you 
get if you plot the activation barrier as a function of iteration number 
for your 30000 iterations?  Does the barrier change?  Does the path change?

Maybe you can do some tests for a small system or if you have a 
realistic model potential you can use that for some quick tests - like 
you did with EMT.

What optimizer did you use?

Jens Jørgen

> Thank you for your time.
> Sincerely
> Sungsik
>
>
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