[CP2K-user] [CP2K:11062] comparing CP2K-DFTB (5.1) and DFTB+ (18.2)

Wei Lai wei.w... at gmail.com
Wed Dec 19 14:50:39 UTC 2018


Dear Juerg,

Thanks for your suggestion.  Parameters I chose previously converged the
results reasonably.  To be more systematic,  I tried the following
combinations without specifying RCUT (I was doing that to make sure it's
less than 1/2 of the box size).  Comparison of these with those I presented
earlier still suggests strong sensitivity to ALPHA and difference from
DFTB+.

Thanks, Wei

Accuracy   GMAX ALPHA      Li-Mulliken-charge H0-energy SCC-energy
1.00E-06     21 0.583             0.57183     -414.5978042 8.302909355
1.00E-10     21 0.583             0.57183     -414.5978042 8.302909355
1.00E-14     21 0.583             0.57183     -414.5978042 8.302909355
1.00E-14     61 0.583             0.57183     -414.5978033 8.302910247
1.00E-14   101 0.583             0.57183     -414.5978027 8.302910732
1.00E-14   101 0.35 (default)     0.572372     -414.6135268 8.288678932




On Wed, Dec 19, 2018 at 3:41 AM <hut... at chem.uzh.ch> wrote:

> Hi
>
> the parameter in the EWALD section are not very user friendly
> (for historical reasons). In your case you should not keep
> RCUT at a small value and change ALPHA.
> It is better to use the default (RCUT calculated from EWALD_ACCURACY
> and ALPHA internally).
> Also you have to make sure that GCUT is big enough for your system
> to give converged values.
> With all these settings you should see the same behaviour as in DFTB+.
>
> 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: "Wei Lai"
> Sent by: cp... at googlegroups.com
> Date: 12/19/2018 04:50AM
> Subject: [CP2K:11061] comparing CP2K-DFTB (5.1) and DFTB+ (18.2)
>
> Dear CP2K users and developers,
>
>   I was testing the DFTB functionality of CP2K and comparing it to DFTB+.
> I was using Li2O (324 atoms) as an example and the CP2K input file is shown
> in the following (without the full coordinates).
>
>   I found CP2K-DFTB results are very sensitive to the choice of Ewald
> (SPME which is the only Ewald method available for DFTB) parameter (ALPHA
> in A^-1).  For a RCUT of 6 A, an estimate of ALPHA is usually 3.5/6=0.583.
> These results actually suggest indeed this is a good estimate.
>   ALPHA Li-Mulliken-charge    H0-energy      Repulsive energy
> SCC-energy    Tot energy
>   0.64     0.571831        -414.5978261 1.790186269
> 8.302889648  -404.5047502
>   0.583   0.57183          -414.5978042 1.790186269
> 8.302909311  -404.5047086
>   0.5       0.57183          -414.5978156 1.790186269
> 8.302899133  -404.5047302
>   0.35     0.572372        -414.6135268 1.790186269
> 8.288678932  -404.5346616
>   0.22     0.610178        -415.6039561 1.790186269
> 7.126741326  -406.6870285
>   0.219   0.611188        -415.6274692 1.790186269            7.090867312
> -406.7464156
>
>   On the other hand, DFTB+ (using Ewald instead of SPME) results are NOT
> very sensitive to ALPHA.  I am not sure what is the unit of ALPHA in DFTB+
> but I tried several values.  A value of 0.219 (hand tuned) in CP2K gave
> similar results to those in DFTB+ with an automatic ALPHA value.
>   ALPHA Li-Mulliken-charge    H0-energy      Repulsive energy
> SCC-energy    Tot energy
>   auto    0.61175023    -415.6390952 1.790189279            7.070521175
> -406.7783847
>   0.338   0.61175319    -415.6391637 1.790189279            7.07041506
> -406.7785594
>   0.64     0.6117653      -415.6394434 1.790189279            7.069981919
> -406.7792722
>   1          0.61178357    -415.6398657 1.790189279
> 7.069327807  -406.7803486
>
>   I am puzzled by this comparison and wondering if you have any insight on
> this.
>
>
> Thanks, Wei
>
>   &GLOBAL
>     PROJECT Li2O
>     RUN_TYPE ENERGY_FORCE
>     PRINT_LEVEL LOW
>   &END GLOBAL
>
>   &FORCE_EVAL
>     STRESS_TENSOR ANALYTICAL
>     METHOD QS
>     &DFT
>       &QS
>         METHOD DFTB
>         &DFTB
>           SELF_CONSISTENT T
>           DO_EWALD        T
>           DISPERSION      F
>           &PARAMETER
>               SK_FILE Li Li     ./Li-Li.skf
>               SK_FILE Li O      ./Li-O.skf
>               SK_FILE O Li      ./O-Li.skf
>               SK_FILE O O       ./O-O.skf
>           &END PARAMETER
>         &END DFTB
>         EPS_DEFAULT 1.0E-12
>         EXTRAPOLATION ASPC
>         EXTRAPOLATION_ORDER 2
>       &END QS
>
>       &SCF
>         SCF_GUESS RESTART ! can be used to RESTART an interrupted
> calculation
>         MAX_SCF 100
>         EPS_SCF 1.0E-7
>         ADDED_MOS 216
>         CHOLESKY INVERSE
>         &SMEAR ON
>           METHOD FERMI_DIRAC
>           ELECTRONIC_TEMPERATURE [K] 300
>         &END SMEAR
>         &MIXING
>             METHOD DIRECT_P_MIXING
>             ALPHA   0.1
>         &END
>       &END SCF
>
>       &POISSON
>          PERIODIC XYZ
>         &EWALD
>           EWALD_TYPE SPME
>           ALPHA  .64
>           GMAX   21
>           RCUT 5
>         &END EWALD
>       &END
>     &END DFT
>
>     &SUBSYS
>      &CELL
>       PERIODIC XYZ
>         A     13.9765253067         0.0000000000         0.0000000000
>         B     0.0000000000        13.9765253067         0.0000000000
>         C     0.0000000000         0.0000000000        13.9765253067
>       &END CELL
>
>       &COORD
>   Li            1.1647105      1.1647105      1.1647105
>   Li            1.1647105      1.1647105      5.8235526
>   Li            1.1647105      1.1647105     10.4823942
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