[CP2K-user] [CP2K:16895] Re: What is the precision on forces emitted by CP2K's energy forces job?

Matt D ucecmtd at gmail.com
Wed Apr 27 08:50:02 UTC 2022

Hi Alex,

The quality of the forces you calculate will depend on the accuracy to 
which the SCF problem is solved. The tolerance for the latter is given by 
EPS_SCF - a typical value for EPS_SCF during a geometry optimisation would 
be around 1e-7 Ha. Another important parameter for the SCF tolerance is 
EPS_DEFAULT, this should be decreased from the default value of 1e-10 to 
1e-14 to complement the value of 1e-7 for EPS_SCF. The error in the forces 
with respect to these parameters should be sqrt(EPS_SCF) < error on force; 
and sqrt(EPS_DEFAULT)  < EPS_SCF.

The default units in CP2K are always atomic units, so the force is in 
Hartree/Bohr. If you want to change the units you put in the input, this is 
possible but I have forgotten the exact syntax. I think it is something 

KEYWORD [unit] 0.025

and the "unit" is replaced by one of the units in this list:


Best wishes,

On Monday, 25 April 2022 at 21:56:44 UTC+1 alexvd... at gmail.com wrote:

> Hi,
> I'm curious what the precision on forces in a cp2k energy_forces job. In 
> particular, how does it depend on various input variables, such as EPS_SCF? 
> Also, in the forces section, the printout says the units are in atomic 
> units. Is that also the default unit for all force dependent convergence 
> criteria, such as in a NEB job?
> Thanks,
> Alex

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