[DFTB-Plus-User] DFTB xTB-GFN2

[James A Charles]

Hi,

I recently saw that you were adding the GFN2 tight binding model to DFTB+ and was quite excited to try it. I did some basic tests with water dimers and trimers and got strange results. Perhaps there is a bug?

Here is for the dimer but similar for the trimer, GFN2 gives a negative, unphysical, binding energy :


model

Calc. binding energy [kcal/mol]

Ref. binding energy* [kcal/mol]

Relative diff. %

mio

4.99247

4.99

0.05

3ob3-1

4.59272

4.99

-7.96

GFN1

4.80922

4.99

-3.62

GFN2

-53.46331

4.99

-1171

*J. Phys. Chem. B 2005, 109, 33, 15677–15683


Is there anything I'm missing?

James Charles, PhD
Senior Research Associate
School of Electrical and Computer Engineering
Purdue University
465 Northwestern Ave,
West Lafayette, IN 47907
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