[CP2K-user] [CP2K:18468] Re: COM drifting

Marcella Iannuzzi marci.akira at gmail.com
Fri Feb 17 14:46:23 UTC 2023

Dear Simone, 

Did you run BOMD with this system? 
It is always better to start sampling with SGCPMD from a stable BOMD.

I don't know how you have determined the cutoff. One way to do it would be 
to calculate the BO forces with increasing cutoff to check the deviation. 
Since the parameters have been tested for the "almost identical system", I 
understand that for that system under the same conditions the COM did not 
drift. Is it so?

Concerning the setting:
The time step is very large. 0.5 would be safer.
EPS_SCF  is rather tight to be a SGCPMD
The preconditions is poor
MAX_SCF_HIST is commented out

However it is difficult to judge without knowing how the wfn's convergence 
is behaving.


On Friday, February 17, 2023 at 2:58:55 PM UTC+1 Simone Ritarossi wrote:

> Dear Marcella,
> I chose the cutoff as the minimum possible. Without COMVEL_TOL there is 
> drifting (along x) that must not be there. I would like to solve the 
> drifting without the forcing of COMVEL_TOL (e.g. by increasing the cutoff 
> so that the forces can be calculated better? )
> The noisygamma was chosen from previous simulations on almost identical 
> systems, as advised by the supervisor.
> Why do you say that " Your settings for SGCPMD look strange." ?
> Many thanks in advance,
> Simone
> Il giorno venerdì 17 febbraio 2023 alle 10:12:09 UTC+1 Marcella Iannuzzi 
> ha scritto:
>> Dear Simone,
>> The cutoff looks indeed small. 
>> Does the COM drift by BOMD? Have you tried without COMVEL_TOL? 
>> Your settings for SGCPMD look strange. 
>> Have you run the needed tests for the nosy-gamma to find the right 
>> parameters?
>> Regards
>> Marcella
>> On Friday, February 17, 2023 at 2:25:00 AM UTC+1 Simone Ritarossi wrote:
>>> Dear cp2k-users,
>>> I have a problem with COM (center of mass) drifting (along x). I'm 
>>> running a LANGEVIN  (SGCPMD) on my  heterostructure, consisting of a GST + 
>>> TiTe2 (633 atoms),  where I consider van der Waals interactions (with 
>>> DFT-D3).  The cutoff is 320 Ry: maybe is it too small? Maybe at a 
>>> temperature of 600K a gamma of 1.9e-3 is too big?
>>> I noticed that by using COMVEL_TOL=0 I have the following behaviour: the 
>>> temperature of the whole system does not correspond to the average 
>>> (weighted according to the number of atoms) of the temperatures of the 
>>> individual atomic species. 
>>> Many thanks in advance,
>>> Simone

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