[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
>> --
>> 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.
>> To post to this group, send email to cp... at googlegroups.com.
>> Visit this group at https://groups.google.com/group/cp2k.
>> For more options, visit https://groups.google.com/d/optout.
>>
>>
>> --
>> You received this message because you are subscribed to a topic in the
>> Google Groups "cp2k" group.
>> To unsubscribe from this topic, visit
>> https://groups.google.com/d/topic/cp2k/RfYbOq3j0DM/unsubscribe.
>> To unsubscribe from this group and all its topics, send an email to
>> cp2k+uns... at googlegroups.com.
>> To post to this group, send email to 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/20181219/623877ff/attachment.htm>
More information about the CP2K-user
mailing list