Dear Catrina
To perform a bilk calculation you will need a "supercell" anyway...
eventhough it is a 1x1x1 supercell for pure bulk phases or bigger ones for
other porpouses. Apart of that the parameters u gave in your mail dosent
help that much to help you.
The cell parameters for a bulk opmitization should be close to the
ideal cristal ... for the same kind of cristal you are trying to model ( HCP
for Zn, wurtizite for ZnO or GaN, and so on ) and for a bulk calculation no
more than 1 unitcell is necessary for construct the suppercell.
Another thing is .... there is nothing wrong in principle if you
want to reproduce the results of somebodyelse ( usually this is my favorite
method to test my pseudopotentials and basis and also other codes), but
instead to try complicated cases like 6x6x3 suppercells which are probably
related with defects ( as Dr. Appostinik has already suggested ) I would do
that for small thing ( like a perfect bulk with few atoms :) )
I dont want to looks arrogant, but the questions u are placing here are
actually more related with basic solid-state physics than with SIESTA.I can
understand you, because I'm a chemist who started to study solid-state not
so long ago and I've done quite a bit of dummy questions here in the
beggining ... If I an give u a hint: is always usefull to expend some time
with some basic solid-state before to run the calculations ... it helps a
lot!
Regards
NH
On Tue, Nov 25, 2008 at 4:49 PM, catrina desport
<[EMAIL PROTECTED]>wrote:
> Dear Andrei Postnikov,
>
> I am sorry if my words were confusing. Actually, it is not the matter of
> imitating at all. I just wanted to know if having supercell for some systems
> like bulk hexagonal helps to get better answers.
>
> I didn't enclose their article to keep it from judgements, but in a
> presentation I found from the work they did, I saw the below lines:
>
> Bulk ... (hexagonal system)
> SIESTA: TM pseudopotential, ... basis, ... Ry mesh cutoff, LDA
> Piezoelectric constant
> Berry Phase: e33=... C/m2
> Our O(N) method: e33=... C/m2
> 6×6×2 supercell
>
> Again, I insist, it is not the matter of imitating at all, just wanted to
> know if there's a helpful method to get reasonable parameters for hexagonal
> systems, especially those which are abit unstable.
>
> I hope to have your valuable response.
> Regards,
> Catrina
>
> ------------------------------
> *From:* "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
> *To:* [email protected]
> *Sent:* Tuesday, November 25, 2008 6:32:02 PM
> *Subject:* Re: [SIESTA-L] URGENT (supercell for bulk)
>
> > To all respected siesta users:
> >
> > Considering
> > an article on a hexagonal lattice, written by authors who have worked
> > with siesta, I have encountered that they have used 6x6x2 supercell for
> > their "bulk" system !!!
>
> Dear Catrina:
> if it is really supercell used in their calculation and not just
> superc: Internal auxiliary supercell
> message, then they should have had a good reason for doing it
> (usually, modeling a point defect, ....) and not just bulk?
>
> > I need to know how they have done it to
> > generate the appropriate supercell
>
> I'd guess, rather by hand or by using the SuperCell block
> (once, and then exporting the generated coordinates in the input file)
>
> > for better optimization for my
> > system as well.
>
> I wonder how can supercell help in "better optimization of your system"?
>
> > Please do guide me, it is very urgent for me.
>
> This is difficult for two reasons:
> you do not explain what you want to do,
> and refer to other peoples' work which you apparently want to imitate,
> without giving any details or reference.
>
> Best regards
>
> Andrei Postnikov
>
>
