[CP2K:1694] Re: DFTB charge equilibration discrepancy

[Juerg Hutter]

Hi

so it's not Ewald, good.
Without more information it is still wild guessing:

Could it be an odd number of electrons? What happens if
you are using "LSD" for NO?

Could it be that your DFTB+ run is using a l-dependent
hardness by default? CP2K has only a single hardness
value per atom implemented.
Or is DFTB+ taking another hardness value from the
input file, CP2K is using the s-value.

regards

Juerg

----------------------------------------------------------
Juerg Hutter                   Phone : ++41 44 635 4491
Physical Chemistry Institute   FAX   : ++41 44 635 6838
University of Zurich           E-mail: hut... at pci.uzh.ch
Winterthurerstrasse 190
CH-8057 Zurich, Switzerland
----------------------------------------------------------


On Tue, 13 Jan 2009, Nir wrote:

>
> Hi Juerg,
>
>> there might be several reasons for this problem.
>> To get more information could you do the following tests:
>>
>> - run both programs without EWALD (and PERIODIC NONE in CP2K)
>>    in order to verify that we agree on the basics
>
> Thank you for your speedy reply.  Unfortunately turning off the Ewald
> sums in both codes (and using PERIODIC NONE in CP2K) did not produce
> agreement.  I also tried doing the same by using the "cluster" option
> with DFTB+ without success.  Is there anything else you can suggest to
> try?  Again, DFTB/DFTB+ and CP2K agree very well for systems such as
> CO, H2O and CH4, but disagree for CO and NO.  I'm using the scc input
> files provided by CP2K for all three codes.
>
> Thanks again,
>
> Nir
>
>>
>> - Converge all EWALD parameters in both codes in order to
>>    exclude problems with different implementations
>>
>> When we tested the implementation we reached agreements
>> with the reference code (DMON) far better than 1%
>>
>> best regards
>>
>> Juerg
>>
>> ----------------------------------------------------------
>> Juerg Hutter                   Phone : ++41 44 635 4491
>> Physical Chemistry Institute   FAX   : ++41 44 635 6838
>> University of Zurich           E-mail: hut... at pci.uzh.ch
>> Winterthurerstrasse 190
>> CH-8057 Zurich, Switzerland
>> ----------------------------------------------------------
>>
>> On Thu, 8 Jan 2009, Nir wrote:
>>
>>> Hi All,
>>
>>> I have been benchmarking the DFTB implementation in CP2K against a
>>> version of the DFTB code from Prof. Frauenheim's group (www.dftb.org)
>>> and have run into some problems.  FYI, the DFTB code I used force
>>> matches to DFTB+ to within 1%.  Specifically, for this problem we are
>>> interested in systems containing C, N, O, and H.  For the benchmarking
>>> tests I'm talking about, both codes were run using charge
>>> equilibration (scc) and Ewald sums, without dispersion, and using
>>> identical parameter files.  Similar very low SCF convergence criteria
>>> were used for both codes.
>>
>>> For most systems I tested (e. g., CH4, H2O, CN, diamond), the two
>>> codes compared very well and the forces and computed energies matched
>>> to within ~1%.  However, the forces and energies were considerably off
>>> for systems containing C-O, N-H, and N-O bonds (e. g., CO, NH3 and
>>> NO2, respectively).  I hacked into both codes and saw that the
>>> repulsive forces are virtually identical for both CP2K and the DFTB
>>> code, but that for some reason they equilibrate to different charges
>>> for the above systems.   Any help or insight into solving this problem
>>> would be greatly appreciated.  I uploaded a tar file called
>>> nir_dftb.tar of sample input and output files for a single NH3
>>> molecule containing the following files (with hopefully self-
>>> explanatory names):
>>
>>> cp2k.nh3_single.inp
>>> cp2k.nh3_singe.out
>>> cp2k.charges.dat
>>> DFTB.nh3_single.out
>>> DFTB.FRC_nh3_single.DAT
>>> DFTB.CHR_nh3_single.dat
>>
>>> In case it matters, I ran cp2k.popt on a single node on a Linux-x86-64
>>> machine compiled with the intel fortran compiler.
>>
>>> Thanks for your help!
>>
>>> Nir
> >
>