[CP2K-user] [CP2K:13072] Re: Different values of "Total energy"  and " ENERGY| Total FORCE_EVAL" for a QS-DFT cal with no smearing.

hut... at chem.uzh.ch hut... at chem.uzh.ch
Wed Apr 8 09:10:37 UTC 2020


there are two parts to the energy/force calculation in CP2K.
1. SCF iteration, CP2K reports the energy calculated with the
   input density and the wfn gradient.
   At the end of the cycle, the output density of the last step
   is passed on.
2. Final energy is calculated from the output density of the SCF
   cycle together with consistent forces.

If the SCF energy and the final energy are considerably different,
you have a problem with the SCF convergence criteria.


Juerg Hutter
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland

-----cp... at googlegroups.com wrote: -----
To: "cp2k" <cp... at googlegroups.com>
From: "Unmesh Mondal" 
Sent by: cp... at googlegroups.com
Date: 04/07/2020 11:19AM
Subject: [CP2K:13072] Re: Different values of "Total energy"  and " ENERGY| Total FORCE_EVAL" for a QS-DFT cal with no smearing.

Dear Users,

As a follow up to my previous question, which subroutine of the code deals with the calculation of  final free energy (" ENERGY| Total FORCE_EVAL") from the DFT energy ("Total energy") in QS-DFT? 

The difference in the above mentioned quantities raises a doubt about the forces on the atoms used in dynamics. Can someone please let me know which energy quantity (amongst the two) is used to calculate the forces on atoms (I have not used any smearing in the calculation)?  

Please correct me if I have misunderstood any part.  

Unmesh Mondal

On Thursday, March 19, 2020 at 2:32:40 AM UTC+5:30, Unmesh Mondal wrote:
 Dear Cp2k users,

For a DFT calculation with no smearing, we expect the "Total energy"  and " ENERGY| Total FORCE_EVAL" to be same, as mentioned in 

But, for a PIGLET MD simulation where cp2k is the client and i-pi(http://ipi-code.org/) is the host, I find the above two quantities to be different for a particular scf step. Attached is the output(pimd_gle_4.out: line number: 8442) where I find this anomaly.

(The job script fires multiple instances of the cp2k executable with each running on separate node.)

What can be the reason for such an anomaly?
How to address the anomaly?

Also, attaching the cp2k input(in.cp2k) for the same. 

Unmesh Mondal
IISER Pune. India
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