[CP2K-user] [CP2K:12777] Negative frequencies in vibrational analysis

sumit agrawal sumitag... at gmail.com
Fri Jan 17 10:39:07 UTC 2020

Hi Lucas Lodeiro,
Thanks for your response. Actually I want to do vibrational analysis in the 
matrix such as Ar and N2. So basically I want to make a cubic cell of the 
Ar or N2 and i want to put my molecule of interest inside this cube. So can 
you tell me what is the exact procedure to do such kind of calculations? 
Should I have to make a cubic cell first then optimized first and after 
optimization of this cubic cell I have to put my molecule of interest 
inside this and again I have to optimize this system? or simply should I 
make a system of interest and optimize this. 

And one more inquiry I want that my interest in systems has less than 100 
atoms so should I have to apply PBC of such kind of systems?

Thanks, Sumit

On Thursday, January 16, 2020 at 7:31:13 AM UTC-8, Lucas Lodeiro wrote:
> Hi Sumit,
> If a vibrational mode presents a "negative" frequency (really it is an 
> imaginary frequency, due to the hessian element is the negative one), it is 
> because your system is not at minimmum stationary point (it could be in a 
> 1° order saddle point). To fix it you must to do a geometry optimization 
> first, to reach a stationary point, then a vibrational analysis will have 
> useful information.
> It is important to note that a vibrational analysis with Harmonic 
> approximation does not have sense if you do not found a stationary point on 
> the Potential Energy Surface.
> Regards - Lucas Lodeiro
> El mar., 14 ene. 2020 a las 9:23, sumit agrawal (<sum... at gmail.com 
> <javascript:>>) escribió:
>> When I am trying to do to vibrational analysis, there are some modes that 
>> have negative frequencies. How can I solve this issue? 
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