[DFTB-Plus-User] Optimizing polyyne chain in DFTB+ for low BLA range: Need guidance

[Khadidja Chaib Edderraa]

Hello,
I am writing to you to provide further details regarding the structure I
used before optimization for the chain. The structural parameters I
employed were d1=1.51 Å and d2=1.22 Å. However, after performing the
relaxation, I obtained a BLA value of approximately 0.11 Å, which is
significantly larger than the range predicted by DFT (0.01-0.05 Å).

On Fri, Jun 2, 2023, 12:10 Khadidja Chaib Edderraa <
k.chaibedderraa at univ-chlef.dz> wrote:

> Dear ,
>
> I hope this email finds you well. I am currently working on optimizing a
> polyyne chain using DFTB+ and aiming to achieve a low range of bond length
> alternation (BLA) in my system. After exploring the available resources, I
> believe your expertise in DFTB+ could provide valuable insights and
> guidance for my research.
>
> To provide some context, my research focuses on  ensuring that the
> molecular structure represents the most stable configuration and optimizing
> the polyyne chain is crucial for achieving BLA values  that align closely
> with experimental and other simulation data.
>
> The specific details of the polyyne chain I'm studying are as follows:
> - Number of carbon atoms: 2 carbon
> - Parameterisation data (Slater-Koster files)  used to perform
> calculations : 3ob, mio, ob2, matsi
> - Geometry optimization:  using  conjugate gradient algorithm but have not
> obtained the desired results.
>
> My main questions are as follows:
> 1. What are the recommended optimization settings or parameters for a
> polyyne chain in DFTB+ to achieve a low BLA range?
> 2. Are there any specific convergence criteria that I should consider
> during the optimization process?
> 3. Are there any DFTB+ features or functionalities that could be
> particularly useful for optimizing polyyne chains and reducing the BLA
> range?
>
> Thank you very much, and I look forward to your response.
>
> Sincerely,
> Khadidja
> k.chaibedderraa at univ-chlef.dz
>
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