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

[siddheshwar chopra]

Hello Karol,
I hope you dont mind me asking you some questions, as I am very new to
dftb. Thank you for your kind help.
I really dont understand what you mean by using same hamiltonian. Do you
mean the optimized geometry (So)? I will however send you input files
tomorrow positively.
I optimize the ground state geometry. Then I use the newly generated
(optimized) "geom.out.gen" as the input coordinates for second derivatives.
Then I use the hessian for modes. Is that right?

Regards,


On Mon 7 May, 2018 10:46 pm Karol Strutynski, <strutynski.karol at gmail.com>
wrote:

> 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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