[CP2K-user] [CP2K:14677] Calculating dipole moments for static dielectric constant calculation. Please help me decide whether and how to use Ewald summation.

[hut... at chem.uzh.ch]

Hi

if you use Quickstep (DFT) then all calculations will use 
the Ewald method unless PERIODIC NONE is specified.
The EWALD section will not be used.
This means you should use hte periodic dipole moment for your
calculation.

regards

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: "Stns" 
Sent by: cp... at googlegroups.com
Date: 02/03/2021 11:27PM
Subject: [CP2K:14677] Calculating dipole moments for static dielectric constant calculation. Please help me decide whether and how to use Ewald summation.

I would like to repeat calculations of the static dielectric constant that someone did years ago with a different code, for use in other calculations.  My basic setup is below.

I'm not an expert and it's a challenge.  One previous problem was that I did not realize I was not calculating "traditional" dipole moments that are compatible with the fluctuation formula used in exercises like the one at the link in red below.  I now include "PERIODIC FALSE" (please see my setup at the bottom of this message) and the problem seems to have been fixed, but I mention it here in case it is not.
https://www.cp2k.org/exercises:2018_uzh_acpc2:mol_sol

The issue now is that I have realized I should be using Ewald summation in my periodic boundary conditions.  I thought I was (that it was the default).  In my setup below that I have been using, I have:

    &POISSON
       PERIODIC XYZ 
    &END

However, I came across an example input file in a CP2K exercise online and saw that he included explicit language related to Ewald summation, so it appears I have not been using it so far.  The example uses:

          &POISSON
       &EWALD
         EWALD_TYPE ewald
         ALPHA .45
         GMAX  19
       &END EWALD
     &END POISSON
Could someone please point me in the right direction?  Should I replace my simple "PERIODIC XYZ" with the example directly above (in red)?  How can I figure out reasonable values for ALPHA and GMAX if so?  Any advice would be very helpful.  Thank you.



My setup (below).
      &GLOBAL
   PROJECT X
   RUN_TYPE MD
 &END GLOBAL
 &FORCE_EVAL
   STRESS_TENSOR  ANALYTICAL
   METHOD  Quickstep
   &DFT
     &PRINT
       &MOMENTS
       FILENAME = moments
       ADD_LAST NUMERIC
       PERIODIC FALSE
       &EACH
         MD 1
       &END
       &END MOMENTS
     &END PRINT
     BASIS_SET_FILE_NAME BASIS_MOLOPT
     POTENTIAL_FILE_NAME POTENTIAL_SET
     CHARGE 0
     MULTIPLICITY 1
     &MGRID
        CUTOFF [Ry] 600
        REL_CUTOFF [Ry] 60
     &END
     &QS
        METHOD GPW
        EPS_DEFAULT 1.0E-10
        EXTRAPOLATION ASPC
        EXTRAPOLATION_ORDER 4
     &END QS
     &POISSON
        PERIODIC XYZ 
     &END
     &SCF
       SCF_GUESS ATOMIC 
       MAX_SCF 30
       EPS_SCF 1.0E-6 
       &OT
         PRECONDITIONER FULL_SINGLE_INVERSE
         MINIMIZER DIIS
       &END OT
       &OUTER_SCF 
         MAX_SCF 10
         EPS_SCF 1.0E-6 
       &END
       &PRINT
         &RESTART OFF
         &END
       &END
     &END SCF
     &XC
       &XC_FUNCTIONAL
          &PBE
          &END
       &END XC_FUNCTIONAL
       &XC_GRID
             XC_DERIV  SPLINE2_SMOOTH
             XC_SMOOTH_RHO NN50
       &END XC_GRID
       &VDW_POTENTIAL
          POTENTIAL_TYPE PAIR_POTENTIAL
          &PAIR_POTENTIAL
             PARAMETER_FILE_NAME dftd3.dat
             TYPE DFTD3
             REFERENCE_FUNCTIONAL PBE
             R_CUTOFF [angstrom] 16
          &END
       &END VDW_POTENTIAL
     &END XC
   &END DFT
   &SUBSYS
     &CELL 
       ABC X X X
     &END CELL
     &COORD
       XXX
     &END COORD
     &TOPOLOGY
     &END
     &KIND X
       BASIS_SET DZVP-MOLOPT-SR-GTH
       POTENTIAL GTH-PBE-q9
     &END KIND
   &END SUBSYS
 &END FORCE_EVAL
 &MOTION
   &MD
      XXX
   &END MD
   &PRINT
     …
   &END PRINT
 &END MOTION  
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