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

Wei Lai wei.w... at gmail.com
Wed Dec 19 18:09:22 UTC 2018


Dear Juerg,

I have done further testing and may be closer to find out the source of
this discrepancy.  Basically, non-SCC results are "consistent" between CP2K
and DFTB+.  Fore SCC-DFTB, they differ in whether to include SCC at the
first scf (it also seems that DFTB+ applies non-scc scf first before
applying SCC energy).  I don't know the coding thoughts of SCC well enough
but I am wondering which one of these two is the better way.  Regarding why
CP2K results are sensitive to ALPHA I guess there are many local energy
minimums.

Thanks, Wei

CP2K:
Parameters Li-Mulliken-charge H0-energy SCC-energy
NonSCC full scf 0.737779     -417.18328600
SCC-1scf                 0.737779     -355.69044000 0
SCC-2scf                 0.720362     -361.83972460 0.137714872

DFTB+:
NonSCC full scf 0.737791      -417.18197790
SCC-1scf                 0.737791      -417.18197790 10.2841704
SCC-2scf                 0.711388      -417.10728727 9.561284596

On Wed, Dec 19, 2018 at 9:50 AM Wei Lai <wei.w... at gmail.com> wrote:

> 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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