[CP2K-user] [CP2K:20264] imaginary frequencies of water dimer even with tight convergence parameters

[Muhammad Rafiq]

hi sir i have also problem of 1 negative frequency in my calculation i have 
tried a lot of times with different parameters


On Friday, January 27, 2017 at 12:13:21 AM UTC+8 Ali KACHMAR wrote:

> Hi Luis,
>
> BTW, The one water molecule is not also straight forward. But, I can 
> assure you if you do for one water molecule you will do for 2, 3, 4 
> molecules.
>
> Don't be surprised! Getting negative frequencies is quite common not only 
> in cp2k, but also in other DFT codes. 
>
> those are the frequencies for H2O
>         2.165588
>        64.392500
>       146.662981
>      1613.021758
>      3717.933517
>      3822.394550
>
> You are not missing anything rather than you have to insist to get 
> converged geometries.
>
> Best, Ali
>
> On Thu, Jan 26, 2017 at 5:41 PM, Matt W <MattWa... at gmail.com> wrote:
>
>> 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.kac... at gmail.com> 
>>> 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> 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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>>>
>>>
>>>
>>> -- 
>>> Luis A. Ruiz Pestana, PhD
>>> Postdoctoral Fellow
>>> University of California, Berkeley
>>> Lawrence Berkeley National Laboratory
>>> Berkeley, CA 94720
>>>
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