[CP2K-user] [CP2K:17223] Re: SG-CPMD/cons. Q

Marcella Iannuzzi marci.akira at gmail.com
Thu Jun 23 14:07:41 UTC 2022

Dear Alexandra

If you properly selected the noisy gamma and the equipartition theorem is 
satisfied, the generated  Langevin dynamics should sample the canonical 


On Tuesday, June 21, 2022 at 12:44:20 PM UTC+2 a.celi... at gmail.com wrote:

> Dear cp2k-users,
> thanks to Marcell's suggestions and to Onofrio:
> -Always start sgcpmd from a well converged wfn obtained along a standard 
> BOMD run with diagonalisation and smearing
> -  Let the first steps run on many scf iterations if needed, i.e., set 
> MAX_SCF large enough
> -  But use a relative large eps_scf. The wfn is not going to be optimised 
> as in the BOMD, energy convergence  around 10^-5 is desirable
> - Use FULL_ALL preconditioner + ASPC
> - Use a small time step
> - Tune properly GAMMA and NOISY_GAMMA
> Now my calculations are converging! Thanks a lot! Per MD step roughly 5 
> iterations.
> My system is water/Pt(111),  therefore I used the GAMMA and NOISY_GAMMA 
> from Lan, Jinggang, Jürg Hutter, and Marcella Iannuzzi. "First-principles 
> simulations of an aqueous CO/Pt (111) interface." *The Journal of 
> Physical Chemistry C* 122.42 (2018): 24068-24076.
> My question is regarding the cons. Q. In ENSEMBLE NVT the cons. Q is equal 
> to the total energy of my system plus energy of thermostat. The energy of 
> the thermostat can be also printed (for only NVT ENSEMBLE) and I was able 
> to verify it. In ENSEMBLE LANGEVIN, which is also at constant temperature, 
> the cons. Q is equal to the total energy of my system. Is that correct? 
> Maybe I am missing something, because I would interpret it as my system is 
> NVE instead of NVT. Can anybody enlighten me, please?
> I attached the plots of the energies (Hartree units), E_T = cons. Q - Ek - 
> Ep in case of Langevin and NVT ensemble. I know that is a very short 
> simulations but it is just for getting some understanding.
> Many thanks in advance,
> Alexandra

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