[CP2K-user] [CP2K:11289] Convergence problems with DFT+U in NPT ensemble

Krack Matthias (PSI) matthia... at psi.ch
Tue Feb 19 07:57:53 UTC 2019

Dear Ivan

I am wondering, if you performed a CELL_OPT run for your system in advance to relax the cell for a given external pressure? It is difficult to guess from the information you provide what the problem is. A cell change can also cause, of course, a change of the ground state. Especially during the initial part of a NPT_F run quite large cell fluctuation can occur.


From: cp... at googlegroups.com <cp... at googlegroups.com> On Behalf Of Ivan Scivetti
Sent: Montag, 18. Februar 2019 11:19
To: cp2k <cp... at googlegroups.com>
Subject: [CP2K:11289] Convergence problems with DFT+U in NPT ensemble

Dear CP2K community,

I am computing a transition metal oxide for which I am applying DFT+U corrections in a supercell composed of 384 atoms.
To analyse structural properties at room temperature (295K) and standard pressure (1 atm) I need to carry out MD simulations. Due to the complexity of the system (of hexagonal symmetry), I start with the NVT ensemble and eventually reach equilibration. Electronic convergence runs smoothly and efficiently with the OT scheme. Since I do not know the range of the supercell volumes that corresponds to a pressure of 1atm, I started from the experimental values but, as expected, I get average pressures of the order of 500 to 1000 bars depending on the composition of the system. I could keep trying with different volumes and approach to the desire 1 atm pressure. This task, however, is very demanding and rather cumbersome.
I then decided to consider the NPT_F ensemble. However, the electronic DFT+U energy starts increasing significantly during the first steps of the simulation and, eventually, convergence problems start to manifest due to the Mulliken population analysis, with a negative contribution to the DFT+U energy. I could also try the LOWDIN method for charges but forces are not available for this scheme. Thus, it seems that my settings for the NPT_F ensemble are not appropriate for this DFT+U simulation. I describe the relevant MD settings of the input file below:

    Timestep 0.5
    Steps 2000
    Ensemble NPT_F
    Temperature 300.0
       REGION massive
       TYPE CSVR
         TIMECON [fs] 10.
       &END CSVR
    &End Thermostat

     Pressure 1.0
     TIMECON [fs] 10.
   &End barostat

&End Motion

 The message I obtain is the following
 *** WARNING in dft_plus_u.F:1457 :: DFT+U energy contibution is negative ***
 *** possibly due to unphysical Mulliken charges. Check your input, if    ***
 *** this warning persists or try a different method!                     ***

Again, this problems does not arise with NVT simlation, only with NPT. I am wondering if I need of an extra flag in the motion/thermostat session to "tame" the MD run and the electronic convergence. I have carried out an extensive research in the web but it seems there is no previous record of such a type of simulation with CP2K.

Any help would be appreciated.
Thank you very much in advance.

You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+uns... at googlegroups.com<mailto:cp2k+uns... at googlegroups.com>.
To post to this group, send email to cp... at googlegroups.com<mailto:cp... at googlegroups.com>.
Visit this group at https://groups.google.com/group/cp2k.
For more options, visit https://groups.google.com/d/optout.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20190219/a5a6579b/attachment.htm>

More information about the CP2K-user mailing list