[CP2K-user] [CP2K:13601] strange curve of the binding energy of Na-Cl

[Patrick Gono]

Dear Mejdeddine,

You are using a non-periodic Poisson solver, suitable for this system of
isolated atoms. However, the cell dimensions and atomic coordinates have to
be chosen in such a way that the electronic density on the edges of the
unit cell is negligible. Keep in mind that the cubic unit cell is situated
with one corner in location (0, 0, 0) and the opposite corner in (10, 10,
10) Center the atoms in the middle of the cell, either manually, or by
switching on the CENTER_COORDINATES
<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/SUBSYS/TOPOLOGY/CENTER_COORDINATES.html>
statement
in the TOPOLOGY
<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/SUBSYS/TOPOLOGY.html>
section,
which should center them in the middle of the unit cell by default.

Apart from that, I don't see any other immediate issue. What binding energy
plot do you get? What is strange about it?

Yours sincerely,
Patrick Gono

On Mon, 6 Jul 2020 at 14:56, mejdeddine mokhtar <mejdit... at gmail.com>
wrote:

> Dear CP2K developers and users,
>
> I've tried to compute the binding energy of Na _ Cl (singlet state so the
> Multiplicity should be 1)but I got a strange curve at large distances. I
> don't have a lot o experience in using cp2k so I attached the script that
> I've used to calculate the potential energy at varying distance. Could
> someone check if I did something wrong? any help would be appreciated.
>
> &GLOBAL
>     PROJECT NaCl
>     RUN_TYPE ENERGY
> &END GLOBAL
>
> &FORCE_EVAL
>
>   METHOD Quickstep
>   &DFT
>       BASIS_SET_FILE_NAME BASIS_MOLOPT
>       POTENTIAL_FILE_NAME GTH_POTENTIALS
>       CHARGE 0
>       MULTIPLICITY 1
>
>     &MGRID
>        CUTOFF [Ry] 400
>     &END
>
>     &QS
>        METHOD GPW
>        EPS_DEFAULT 1.0E-6
>     &END
>
>     &POISSON                      # POISSON solver for non-periodic
> calculation
>        PERIODIC NONE
>        PSOLVER WAVELET
>     &END
>     &SCF
>       SCF_GUESS ATOMIC ! can be used to RESTART an interrupted calculation
>       MAX_SCF 300
>       EPS_SCF 1.0E-6 ! accuracy of the SCF procedure typically 1.0E-6 -
> 1.0E-7
>       &OT
>         PRECONDITIONER FULL_SINGLE_INVERSE
>         MINIMIZER DIIS
>       &END OT
>       &MIXING
>          METHOD BROYDEN_MIXING
>          ALPHA  0.4
>          BETA   1.5
>          NBROYDEN 8
>       &END MIXING
>       &OUTER_SCF ! repeat the inner SCF cycle 10 times
>         MAX_SCF 100
>         EPS_SCF 1.0E-5 ! must match the above
>         OPTIMIZER  DIIS
>       &END
>     &END SCF
>     &XC
>       &XC_FUNCTIONAL PBE
>       &END XC_FUNCTIONAL
>     &END XC
>   &END DFT
>    &SUBSYS
>     &CELL
>       ABC [angstrom] 10.00 10.00 10.00
>     &END CELL
>     &COORD
> Na    0.0 0.0 0.0
> Cl    0.0 0.0 MYDIST
>     &END COORD
>     &TOPOLOGY
>       CONNECTIVITY GENERATE
>       &GENERATE
>         BONDLENGTH_MAX 9
>       &END
>     &END
>     &KIND Na
>       BASIS_SET DZVP-MOLOPT-SR-GTH
>       POTENTIAL GTH-PBE
>     &END KIND
>     &KIND Cl
>       BASIS_SET DZVP-MOLOPT-SR-GTH
>       POTENTIAL GTH-PBE
>     &END KIND
>   &END SUBSYS
> &END FORCE_EVAL
>
>
> The bash script used to get the calculation running is the following:
>
> rm -f ener_profile
>
> #for dist in `seq 2.3 0.1 6.0`
> for dist in 4.0 5.0 6.0 7.0 8.0 10.0; do
>
>   #
>   # compute energy
>   #
>   echo "Computing potential energy for distance $dist"
>   sed "s/MYDIST/${dist}/g" mode1.inp > inp
>   cp2k.popt inp > out
>   ener=`grep ' ENERGY| Total FORCE_EVAL' out | awk '{print $NF}'`
>   echo $dist $ener >> ener_profile
>
> done
>
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