[CP2K:1692] DFTB charge equilibration discrepancy

[Juerg Hutter]

Hi Nir

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

- 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
> >
>