[ase-users] Optimization - fmax in NEB

[Sungsik Kim]

I am sorry.

Because the activation energy for dissociative adsorption of methane is
zero,

I ran associative desorption of oxygen on platinum surface with EMT
calculator.

That is 0.625eV.

Sungsik




2013/4/2 Sungsik Kim <sungsik312 at gmail.com>

> Hello, Jens
>
> Thank you for your help.
>
> I used QuasiNewton optimizer with fmax=0.05 for initial and final surface
> potential energy.
>
> And I used FIRE optimizer with fmax=0.05 for NEB calculation with DACAPO
> calculator.
>
> However, the calculation had not been completed, I changed fmax to 0.5 to
> reduce computing time.
>
> 30000th does not mean iteration. It is the number of calculation in
> optimization on python shell.
>
> I tested path and energy barrier with EMT calculator by your comment
> because DACAPO calculator take lots of time.
>
> In this run, I used Quasinewton optimizer for initial and final state and
> FIRE for NEB, all with EMT calculator.
>
> First I ran it with different fmax such as 1.0, 0.5, 0.1, 0.05, and 0.01
> in NEB calculation.
>
> I got 0.625ev for activation energy for those fmax = 0.05.
>
> Second I run it with fmax = 0.05 with different iteration such as 5, 10,
> 20, 30, 40, 50.
>
> In this run, I still got the same activation energy, 0.625eV.
>
> Path is getting more refined until 30 iteration. But after 40 it is a
> little changed. it is slightly fluctuated initially.
>
> Finally, even though I used different fmax such 0.5 and different
> iteration, I got the same activation energy.
>
> Does it mean that I can used fmax= 0.5 to get activation energy for
> dissociative adsorption of methane on Pt with DACAPO calculator?
>
> Thank you for your help again.
>
> Sincerely
>
> Sungsik
>
>
>
>
>
> 2013/4/2 Jens Jørgen Mortensen <jensj at fysik.dtu.dk>
>
>>  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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>>
>>
>>
>
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