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["Semichaevsky, Andrey " <Andrey_Semichaevsky@uml.edu>]

Hello George,

 

Can you split your problem into:

1) calculation of the optical properties of a carbon nanotube; ABINIT GWA may be very slow for a large

system like you described but you may do just one k-point (Gamma) to estimate the "scissor operator",

i.e., the self-energy - related shift of the conduction band relative to the valence band;

 

2) calculation of the interatomic force-fields for CNT <->aminoacid interactions? This can be done

without an explicit use of GWA but using the estmated direct bandgap from 1).

 

Regards,

 

Andrey Semichaevsky

 

---

From: George Abadir [mailto:georgea@ece.ubc.ca]
Sent: Thu 10/25/2007 2:46 PM
To: forum@abinit.org
Subject: Re: [abinit-forum] Carbon nanotube - amino acid simulations

Dear Fabien,
                     Thanks alot for your response. What I need is to
include just one molecule of adsorbed amino acid on a 7-8 nm long tube.
Is this still too complex to do within the GWA? If so, are there any
crude corrections to the bandgap calculated from the DFT within the LDA
or GGA? Are there other methods to calculate the bandstucture of such a
system? I actually need an accurate bandgap because I am concerned with
the optical properties of the NT as well as the electronic ones.
                     Thank you very much for your help,
Regards,
George

Fabien Bruneval wrote:

> Dear George,
>
> The GW approximation is indeed implemented in Abinit. However, in
> Abinit it is just meant to calculate the electronic band structure in
> a periodic system.
>
> In principle, the GW approximation can be used to calculate total
> energies and forces, but the calculations are so cumbersome that only
> atoms have been calculated so far (see the work of R. van Leeuwen for
> instance).
>
> If you really want to treat big systems like nanotube + amino acid,
> you can forget about the GW approximation and turn to simpler methods.
>
> I hope to have clarified the situation.
>
>
> Fabien
>
>
>
>
>
>
>
> George Abadir wrote:
>
>> Dear Jean-Christophe,
>>                                   Thank you very much for your reply.
>> I am aware of the VDW problems with DFT. The point is that I need an
>> accurate bandstructure for the CNT. As far as I understand, the GW
>> approximation can do that and it is included in ABINIT. Could you
>> guide me to other packages that can perform the calculations within
>> the GW approximation for my problem? If not,  can ABINIT in principle
>> do the calculations may be at a large computational cost? Or will the
>> size of the supercell be prohibitive in your opinion?
>>                                  Thanks alot for your help,
>> Regards,
>> George
>>
>> Jean-Christophe Charlier wrote:
>>
>>>
>>> Dear George,
>>>
>>> ABINIT is probably not the best code to investigate amino
>>> acids adsorbed on carbon nanotubes because your simulation
>>> will need a large supercell and lot's of vacuum in order to
>>> avoid the interaction between the repeated images.
>>> DFT codes based on localized basis sets (and not plane-waves
>>> like ABINIT) for the expansion of the wavefunctions are probably
>>> more appropriate (i.e. Siesta, Gaussian, ...).
>>>
>>> In addition, DFT has some problem to accurately describe weak
>>> interactions such as VdW that you should observe when an amino
>>> acid is adsorbed at the surface of a nanotube.
>>>
>>>     Regards,                  Jean-Christophe
>>>
>>> On 25 Oct 2007, at 06:12, georgea@ece.ubc.ca wrote:
>>>
>>>> Hi all,
>>>>        I am a new user to ABINIT. My goal is to perform
>>>> simulations  of amino acids adsorbed on carbon nanotubes. My
>>>> question is: can  ABINIT perform such simulations to get the
>>>> electronic properties of  the nanotube after the adsorption of the
>>>> amino acid? If so, is  there a way to visualize my input structure
>>>> after building the  input file and before actually performing the
>>>> simulations?
>>>>        And if not, are there other tools that can do it and have the
>>>> GW approximation?
>>>>        Thanks alot,
>>>> Regards,
>>>> George
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>