[DFTB-Plus-User] [DFTB+: geom.opt periodic 2D graphene] - DFTB-Plus-User Digest, Vol 108, Issue 3

[Mohammad Amir Bazrafshan]

Dear Nuria,

In theoretical calculations, it is important to follow each method. For
example, if you optimize a structure using DFT methods, the bond lengths
may be different from the DFTB method, but the electronic structure will be
close. Remember that the geometry relaxation is important to achieve a
reasonable low energy state of the system.
So if you do not want to change the bond lengths, skip the geometry
optimization.

M.Amir

On Tue, Aug 15, 2023 at 1:30 PM <
dftb-plus-user-request at mailman.zfn.uni-bremen.de> wrote:

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>    1. DFTB+: geom.opt periodic 2D graphene (NURIA AGUILAR CUESTA)
>
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> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 14 Aug 2023 10:59:39 +0000
> From: NURIA AGUILAR CUESTA <naguilar at ubu.es>
> To: "dftb-plus-user at mailman.zfn.uni-bremen.de"
>         <dftb-plus-user at mailman.zfn.uni-bremen.de>
> Subject: [DFTB-Plus-User] DFTB+: geom.opt periodic 2D graphene
> Message-ID:
>         <
> DB8P191MB071693FF40187A0405EBD06FAB17A at DB8P191MB0716.EURP191.PROD.OUTLOOK.COM
> >
>
> Content-Type: text/plain; charset="iso-8859-1"
>
> To whom it may concern,
>
> this is the massage I would like to post to all the list members:
>
> "Hello everyone,
>
> my name is Nuria and a I'm a PhD student in computational chemistry.
> I'm kinda new to DFTB+ calculations.
> I am trying to run a geometry optimization on a periodic 2D graphene with
> variable cell. I tried an isotropic calculation as I do not want the bond
> distances nor the angles between C atoms to change, only as if it's read on
> the manual: 'Isotropic If optimising the lattice, allow only uniform
> scaling of the unit cell.'
> Despite that, the bond lengths and angles keep changing and the periodic
> boundary condition would not replicate the graphene periodic structure
> correctly creating interfaces large enough to consider the structure as a
> graphene sheet.
>
> I tried to run a non variable cell geometry optimization to check the rest
> of the input and the job ended correctly.
>
> The graphene structure has 720 C atoms and the PBC for that is shown below.
> The code I used to run the calculation was the following:
>
>    0.00000000000E+00   0.00000000000E+00   0.00000000000E+00
>    0.44529500000E+02   0.00000000000E+00   0.00000000000E+00
>    0.00000000000E+00   0.42871200000E+02   0.00000000000E+00
>    0.00000000000E+00   0.00000000000E+00   0.30000000000E+02
> }
>
> Driver = GeometryOptimization {
>   Optimizer = SteepestDescent {
>    ScalingFactor = 1.0
>   }
>   LatticeOpt = Yes
>   Isotropic = Yes
>   MaxSteps = 500
>   OutputPrefix = "geom.out"
>   AppendGeometries = Yes
> }
>
> I would greatly appreciate any help to run the calculation properly.
> Thank you all for your help.
>
> Kind regards,
> Nuria
>
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