[DFTB-Plus-User] Geometry is way off while using DFTD3...

[Karol Strutynski]

Hello,
You should run the freq calculations for the structure minimised with the
same hamiltonian. The general path is structure -> optimisation -> freq for
each hamiltonian. I had similar problems when I used wrong hamlitonian for
my minima (without b3 part). Just be sure that dftb_in file for frequencies
has the same hamiltonian part.

To be sure just make separate directories for both cases, and just to be
sure copy the dftb_in from optimization and adjust the driver to
SecondDerivatives{}, and remember to use relatively tigh SCC convergence
for frequencies (e.g. SCCTolerance =1e-8 ).

Other than that it's hard to say without the input files.

Best Regards,
--
Karol Strutynski
CICECO - Aveiro Institute of Materials
Department of Chemistry
Universidade de Aveiro
Office 29.3.25
3810-193, Aveiro, PORTUGAL
Phone: +48 739259476
Mail: strutynski.karol at gmail.com, skarol at ua.pt
ORCID: http://orcid.org/0000-0001-8733-9012On Mon, 7 May 2018 at 17:29,
siddheshwar chopra <sidhusai at gmail.com> wrote:

> Dear Karol,
> Thank you for the information. I used the DFTD3, Grimme's correction. I
had dftb optimization result, and then ran again separately with dftd3{}. I
ran scc with dftd3.
> Please could you throw more light into this?

> Regards,

> On Mon 7 May, 2018 4:47 pm Karol Strutynski, <strutynski.karol at gmail.com>
wrote:

>> Hello,

>> I encountered similar problems myself, but as it turns out it was my
error:
>> You have to be sure that you check the right minima with right
hamiltonian.
>> Practically speaking, the given structure is minima only with Hamiltonian
>> you used to get it.
>> You have to ensure that you have third order terms in your frequency
>> calculations for checking DFTB3 minima.

>> Best Regards,
>> --
>> Karol Strutynski
>> CICECO - Aveiro Institute of Materials
>> Department of Chemistry
>> Universidade de Aveiro
>> Office 29.3.25
>> 3810-193, Aveiro, PORTUGAL
>> Phone: +48 739259476
>> Mail: strutynski.karol at gmail.com, skarol at ua.pt
>> ORCID: http://orcid.org/0000-0001-8733-9012

>> On Mon, 7 May 2018 at 12:11, siddheshwar chopra <sidhusai at gmail.com>
wrote:

>> > Dear Balint,
>> > I am trying to compare DFTB and DFTD3 ground state optimization
results.
>> > I find that total energy obtained in DFTD3 is -2.7300 eV more than the
>> DFTB energy. That seems good to me. But, when I am checking for negative
>> frequencies, I find the geometries to be way off....

>> > For DFTB:
>> >      1   -2.47
>> >      2   -1.34
>> >      3   -0.53
>> >      4   -0.35
>> >      5    0.54
>> >      6    1.42

>> > For DFTD3:
>> >     1  -83.05
>> >      2  -32.67
>> >      3  -24.61
>> >      4    9.71
>> >      5   26.44
>> >      6   39.63

>> > Please tell me how to understand this and how should I proceed?

>> > Regards,
>> > --
>> > Dr. Siddheshwar chopra,
>> > M.Sc., Ph.D (Physics)
>> > Assistant Professor (Physics),
>> > Amity University, Noida, India.

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