[CP2K-user] [CP2K:19846] Re: The treatment of atom mass in the mixing force_evals calculation

[Marcella Iannuzzi]

Dear Xu

The way to do this type of simulation is to apply the alchemical change.
You can find an example input in 

cp2k/tests/FE/regtest-1/Solv_alch_chng.inp

In practice, you need a full set of coordinates that contains both ions, 
this will be the subsystem for the mixed force_eval, which takes care of 
the propagation of the equations of motion, where each atom maintains its 
own mass. Then you prepare other coordinates set for the subsystems of the 
individual force evals. The mixed force_eval needs to have the mapping, 
indicating which atoms of the full set belong to which individual 
force_eval.
I think it is more difficult to explain it in words than understanding  it 
directly from the example input. 

Regards
Marcella


 

On Monday, January 29, 2024 at 11:10:36 AM UTC+1 wangx... at gmail.com wrote:

> Dear CP2K developers, 
>     I am sorry to bother you for a technical detail regarding the 
> treatment of atom mass in the mixing force_evals calculation.
>     I intend to investigate the free energy difference between Na-Cl and 
> K-Cl ion pairs in aqueous solutions through FPMD-based thermodynamic 
> coupling constant integration, i.e., transitioning Na(+) gradually into 
> K(+) using the &MIXED section:
> [image: CP1.png]
> together with the following settings in the &SUBSYS section:
> [image: CP2.png]
>     During the simulation, energies and forces are mixed via lambda to 
> solve the equation of motion. On the other hand, the masses of atoms are 
> also required in the equation of motion. I am wondering how CP2K handles 
> the mass of “Na” mentioned above in simulations with 0<lambda<1. 
> Specifically, is it calculated as 0.5*(mass_Na+mass_K), lambda*mass_Na+(1- 
> lambda)*mass_K, or utilizing another algorithm? Thanks in advance!
>
> Sincerely,
> Xu
>

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