[CP2K:8589] imaginary frequencies of water dimer even with tight convergence parameters

Matt W MattWa... at gmail.com
Thu Jan 26 15:41:52 CET 2017


What could be a harder test case than small water clusters?

Matt

On Thursday, January 26, 2017 at 2:38:56 PM UTC, Luis Ruiz Pestana wrote:
>
> Hi Ali,
>
> Thanks for the response! I am using 400 Ry because I needed it to be the 
> same cutoff that I used in some other AIMD simulations in the 
> condensed phase. Regardless, I have tried the suggested changes and I still 
> get imaginary frequencies. I am quite surprised that cp2k is having a hard 
> time with such simple small systems, am I missing something?
>
> Best,
> Luis
>
> On Wed, Jan 25, 2017 at 9:35 AM, Ali KACHMAR <ali.k... at gmail.com 
> <javascript:>> wrote:
>
>> Dear Luis,
>>  
>> 1. a cutoff of 400 Ry is a bit low for geometry optimization + 
>> vibrational frequency calculations on water systems. Please run your 
>> geometry optimization with tight convergence and a cutoff=550 Ry, 
>> Relcutoff=70 Ry
>>
>> 2. Starting from the optimized geometry, please run your vibrational 
>> analysis calculation using a DX=0.01, and add to the GEO_OPT section 
>>
>>   &GEO_OPT
>>     TYPE MINIMIZATION
>>     OPTIMIZER CG
>>   &END GEO_OPT
>>
>>
>> All the best,
>> Ali
>>
>>
>> On Tue, Jan 24, 2017 at 6:00 PM, <lar... at lbl.gov <javascript:>> wrote:
>>
>>> I am trying to compute the vibrational frequencies of small water 
>>> clusters, and I am having trouble getting rid of imaginary frequencies, 
>>> even for the water dimer, using very tight convergence parameters during 
>>> the geometry optimization.I have also tried to run the simulations with 
>>> periodic boundary conditions, different values of the displacement, etc., 
>>> but I still get a few imaginary frequencies. I have run out of ideas to try 
>>> so any advice will be greatly appreciated. I have attached here the input 
>>> files of the calculations. 
>>>
>>> Thanks for your time!
>>> Luis
>>>
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>>
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>
>
>
> -- 
> Luis A. Ruiz Pestana, PhD
> Postdoctoral Fellow
> University of California, Berkeley
> Lawrence Berkeley National Laboratory
> Berkeley, CA 94720
>
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