[CP2K-user] Some questions on vibrational analysis

[Marcella Iannuzzi]

Dear Azade

You are using a mode selective algorithm, which approximates the Hessian in 
an iterative way, starting from the predefined collective displacement 
vector. 
By assigning the involved atoms you define the initial guess, i.e. the 
space where to look for the modes. 
Whether or not you need to involve one or all molecules, depends on which 
modes you are aiming at. 
Assuming you are looking for the CO stretching and if they are all 
decoupled, one CO only might be enough. 

Being an iterative procedure, increasing the number of iterations enlarges 
the searched space and improves the approximation. The convergence criteria 
and the quality of the approximation are given in the output. As you can 
read, most of the errors of the non-converged modes are quite close to 
those of the the converged ones. 
Restarting the calculation and running more iterations should further 
improve the results. 

Kind regards
Marcella



On Wednesday, October 7, 2020 at 9:47:02 AM UTC+2 aza... at gmail.com 
wrote:

> Dear CP2K community,
>
> I am very new to the vibrational spectroscopy and its implementation with 
> CP2K. I tried to learn as much as I could from the previous conversations 
> and tutorials but there are still a few points which are unclear to me and 
> I hope you can help me with.
>
> I want to study the vibrational spectra of CO molecules on a Pd slab, for 
> various surface coverage. I use a dx value of 0.001A, EPS_DEFAULT 1.0E-12 
> and EPS_SCF 1.0E-10. My questions are the following:
>
> - When I have several CO molecules on the surface, would it make more 
> sense to use the 'INVOLVED_ATOMS' command for only one of the molecules or 
> all of them? My slab is  a 4x4, 5 layers, and I have a maximum of 8 CO 
> molecules on the surface.
>
> - In the output I get the following frequencies. Should I try to have all 
> such frequencies converged? If not, what do the ones which have not 
> converged mean? because when I use molden to look at the vibration modes, 
> the ones which have not converged are also present there, and I can see 
> their vibrational mode.
>
>   VIB|     61.573     0.004846      0.875E-07          0.440E-06           
> YES
>   VIB|    339.290     0.036719      0.409E-06          0.206E-05           
> NO
>   VIB|    652.872     0.001844      0.125E-05          0.424E-05           
> NO
>   VIB|    770.697     0.006918      0.198E-05          0.669E-05           
> NO
>   VIB|    875.719     0.009690      0.136E-05          0.686E-05           
> NO
>   VIB|   1005.729     0.018816      0.949E-06          0.478E-05           
> NO
>   VIB|   1136.781     0.002440      0.148E-05          0.501E-05           
> NO
>   VIB|   1235.179     0.010595      0.101E-05          0.509E-05           
> NO
>   VIB|   1309.728     0.013191      0.167E-05          0.565E-05           
> NO
>   VIB|   1392.711     0.023142      0.900E-06          0.453E-05           
> NO
>   VIB|   1549.969     0.048768      0.437E-05          0.148E-04           
> NO
>   VIB|   1634.615     0.011538      0.126E-05          0.636E-05           
> NO
>   VIB|   1654.494     0.026674      0.106E-05          0.357E-05           
> NO
>   VIB|   1774.636     0.014966      0.445E-06          0.224E-05           
> NO
>   VIB|   1824.832     0.028171      0.743E-06          0.251E-05           
> NO
>   VIB|   1861.463     0.022726      0.311E-06          0.156E-05           
> YES
>   VIB|   1895.821     0.014546      0.352E-06          0.119E-05           
> YES
>   VIB|   1942.303     0.549826      0.229E-06          0.115E-05           
> YES
>   VIB|   1995.758     0.002431      0.178E-07          0.601E-07           
> YES
>   VIB|   2004.175     0.000370      0.339E-07          0.171E-06           
> YES
>   VIB|   2172.351     0.006782      0.137E-10          0.692E-10           
> YES
>   VIB|   2182.669     0.015607      0.129E-10          0.651E-10           
> YES
>
> Sorry if my questions are more towards interpreting the output than 
> performing the test itself. Any explanations are highly appreciated. 
>
> Best regards,
> Azade
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20210115/c4d4300c/attachment.htm>