[CP2K-user] [CP2K:18290] Meaning of SHADOW_GAMMA

[Thomas Kühne]

Dear Amit, 

Gamma_L and Gamma_D of the paper refers to GAMMA and NOISY_GAMMA within the CP2K code. 
SHADOW_GAMMA is the opposite of NOISY_GAMMA and induces a Langevin friction without adding 
the corresponding noise according to the fluctuation-dissipation theorem. This can be used, (i) to determine 
NOISY_GAMMA by reproducing the dissipation as a function of SHADOW_GAMMA, or (ii) to use the 
Langevin equation at the presence of intrinsic noise in the forces e.g. due to the usage of low-precision 
arithmetic. 

Best, 
Thomas Kühne

> Am 02.01.2023 um 23:41 schrieb Amit Gupta <amit.welcomes.u at gmail.com>:
> 
> Following the conversation of this thread: https://groups.google.com/g/cp2k/c/fmZX3_2kivc
> 
> I did a parameter sweep of my system using FIST dynamics, and determined that
> GAMMA = 0.35
> NOISY_GAMMA=1e-5 
> 
> yields best thermostat stability in my system. The paper mentioned in above conversation however uses slightly different terminology of Gamma_L (Langevin friction) and Gamma_D(intrinsic friction). And their values are rather low (1e-8 for Gamma_D and 0 for Gamma_L ). I would like to understand
> 
> 1. How are GAMMA, NOISY_GAMMA, and SHADOW_GAMMA are related to Gamma_L and Gamma_D?
> 2. Does the value I got (0.3 and 1e-5) pass the initial smell test? Or do they look non-physical (I mostly use Nose thermostat but needs to use Langevin for this study for replicating a paper)? 
> 
> Thank you
> 
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==============================
Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
Germany
thomas.kuehne at upb.de
+49/(0)5251/60-5726

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