The ABINIT Users Mailing List ( CLOSED )

["Anglade Pierre-Matthieu" <anglade@gmail.com>]

Hi,

1.
a) DFT is not very fit for VdW forces for instance. If those are
important for you it is possible that DFT will not meet your goals.
b) Usually PW code are not well considered for simulation cells
including lot of vacuum. So the PW-Abinit may not be your best choice.
c) You can try :
-  the BigDFT parf of Abinit. Yet 400 atoms will ikely lrequired a
large computer.
- some linear scaling codes like : http://www.conquest.ucl.ac.uk/
or http://www.uam.es/departamentos/ciencias/fismateriac/siesta/
2. It depends on the previous choices. But you'd better count in days
than in seconds.
3. It also depends on the chosen approximation and on the properties
you are going to calculate ... Chemists usually rely on hybrid
exchange-correlation functional that improves the results for
molecules. With GGA or LDA, for solids, depending on the property
under consideration you usually go from less than 1% off (e.g. cell
parameter) to ~20% off (e.g. elastic moduli).

regards

PMA


On Mon, Jun 2, 2008 at 2:01 PM,  <sk00077@surrey.ac.uk> wrote:
> Dear all,
>
> I want to obtain the energy levels of the defect states on a Multiwalled CNT
> (MCNT).
> The defects are produced due to functionalisation and should be like holes 
> in
> the
> outer wall of the tube (i.e. some carbon atoms missing from their sites). 
> The
> edges
> of these holes may have some other species (e.g. -COOH, -OH) attached to 
> them
> but it is not necessary. I am assuming that (tight binding) DFT is best tool
> for this
> purpose.
>
> I am new to DFT and have no idea of which code will be best for my purpose: 
> I
> do not need very accurate estimates, I have a high end workstation, have no
> local
> expert on DFT and am rather short on time. I have come across the book by
> Richard M. Martin  "Electronic Structure: Basic Theory and Practical 
> Methods",
> but
> it will take some time for me to form my own opinion.
>
> So, could you please guide me a little for the task at hand? Particularly
> regarding
> following:
>
> 1. Whether I should use DFT at all?
>    If yes, would abinit be alright for this purpose?
>    if no, which other (free) packages should I look at?
> 2. How much time will it take to simulate say a ~400 atom tube? (this MCNT 
> will
>  have two concentric tubes of ~200 atoms each and outer tube will have a 
> hole
>  of certain size).
> 3. what can be said about the accuracy of the results? (I am doing 
> experiments
> on
>  this system so want to compare it).
>
> People have done simulation of defects on the CNTs (I came across only 
> Stone-
> Wales defects, and used to study mech. properties). If I missed something I
> would be grateful if you could please point me in right direction.
>
> Thank you very much.
> Shishir.
>



-- 
Pierre-Matthieu Anglade