[DFTB-Plus-User] DFTB (Hbonding damping function + 3rd Order energy term)

[Bálint Aradi]

Dear Mark,

  Today morning one of the authors of the 3rd order paper [J. Phys.
Chem. A., 2007, 111(42): 10861] finally sent me the results of 3rd order
and H-damping calculations with their code for some geometries I've sent
them.  We compared total energies for the sytems H2O, 2H2O, COOH, 2COOH,
CH3COOH- + H2O, each calculated with standard DFTB, DFTB + 3rd order and
DFTB + 3rd order + H-damping, respectively.

   The deviances between their calculation and DFTB+ for those fixed
geometries are below 1e-6 Hartree! That indicates, that the
implementation in DFTB+ should be correct.

  I've also checked the forces again (comparing them to finite
difference total energy calculations) and their are reasonable. So, any
unphysical results obtained with the 3rd order, are likely a
methodological problem (on-site 3rd order with arbitrary empirical
Hubbard-U derivatives not able to describe the desired effect). In that
case, however, I'd again suggest to ask the authors of the paper, as I
do not have much experience with this method.

  Best regards

    Bálint


Ps. If you find out something, it would be kind, if you could post it
also to the list, so other people interested in 3rd order DFTB can
profit from it.

Ps2. The third order DFTB should be part of the next official release of
DFTB+, which is scheduled for this summer.

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/en/~b_aradi


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 252 bytes
Desc: OpenPGP digital signature
Url : http://www.dftb-plus.info/pipermail/dftb-plus-user/attachments/20090406/0d586e38/attachment-0001.pgp