[CP2K-user] [CP2K:21858] Thermostat choice and time constant effects for small Al clusters in MD

[hamid zabihi]

I’m running molecular dynamics simulations for a small aluminum cluster 
(Al₆) and tested two thermostats — *CSVR* and *Nosé–Hoover* — with 
different time constants: very small (5, 15 fs), moderate (200 fs), and 
large (400 fs).

A few questions came up during these tests:

   1. 
   
   Is there any *preferred choice between CSVR and Nosé–Hoover* when 
   simulating *small metallic clusters* (e.g., 4–6 atoms)?
   2. 
   
   With *CSVR*, the system temperature shows large fluctuations (often 
   rising up to ~300 K) instead of stabilizing near the target 100 K, even 
   with small time constants.
   3. 
   
   With *Nosé–Hoover*, the temperature profile is smoother and closer to 
   equilibrium, but using *very small time constants* seems to make the 
   thermostat *too restrictive*, potentially altering the physical nature 
   of the MD trajectory.
   4. 
   
   On the other hand, using *larger time constants (200 or 400 fs)* makes 
   it *difficult for the system to reach thermal equilibrium* within a 
   reasonable simulation time.
   
I have attached the *resulting temperature evolution figures* and the 
corresponding *md.inp files* used for each simulation for reference.

Do you have any recommendations for:

   - 
   
   Choosing between CSVR and Nosé–Hoover for small cluster dynamics
   - 
   
   Selecting an appropriate time constant range to balance thermal 
   equilibration and realistic trajectory sampling
   
Any advice or best practices for such small systems would be greatly 
appreciated.

Thank you!

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