OK, I've had a little lesson just now in supercells. (Thank you, Stephen Todd!)

I think the command is going to be:

load "myfile.xxx" {2 2 2} supercell "2x, x+y, z"

Now, that will load 8 SUPERCELLS, each which will be constructed based on the defined unit cell of the file. (An added UNITCELL parameter would let you set that as well.)

--The cell parameters will be changed
--The symmetry will be set to P1.
--The same "packed" and other load options will apply here, but to the supercell instead of the unit cell itself.

Is it safe to say that the numbers there have to be positive integers? I.E. not "-2x, x-y, -z" ?


Bob



 

On Fri, Sep 24, 2010 at 10:33 AM, P.Canepa <pc229@kent.ac.uk> wrote:

Dear Bob

OK I would like to have both visualize the supercell construction on the screen and export it  with the right cell parameter!

We should have also on right corner the parameters and the space group updated otherwise the user might be confused!

What do you think  ?


However XCRYSDEN works out the supercell simply graphically as it's only acting on  the input for cRYSTAL. Is then crystal which carries out the supercell recalculating the internal symmetry.


Xcrysden simply write something like that into a input file suitable for crystal:

SUPERCEL
 2 0 0
 0 2 0
 0 0 2

I am sorry if I don  answer at all your question.

I am pretty busy this time but I am looking forward to develop the outcar reader  for VASP.

Thank, Piero
--
Please consider the environment before printing this e-mail.

Pieremanuele Canepa
Room 104
Functional Material Group
School of Physical Sciences, Ingram Building,
University of Kent, Canterbury, Kent,
CT2 7NH
United Kingdom

e-mail: pc229@kent.ac.uk
mobile: +44 (0) 7772-9756456
-----------------------------------------------------------
________________________________________
From: Robert Hanson [hansonr@stolaf.edu]
Sent: Friday, September 24, 2010 4:24 PM
To: P.Canepa
Subject: Re: xcrysden supercell

So how can I help you get what you are interested in doing?



On Fri, Sep 24, 2010 at 10:14 AM, P.Canepa <pc229@kent.ac.uk<mailto:pc229@kent.ac.uk>> wrote:
You are right.

the  fractional coordinates don't change you are right!

Thank, Bob
--
Please consider the environment before printing this e-mail.

Pieremanuele Canepa
Room 104
Functional Material Group
School of Physical Sciences, Ingram Building,
University of Kent, Canterbury, Kent,
CT2 7NH
United Kingdom

e-mail: pc229@kent.ac.uk<mailto:pc229@kent.ac.uk>
mobile: +44 (0) 7772-9756456
-----------------------------------------------------------
________________________________________
From: Robert Hanson [hansonr@stolaf.edu<mailto:hansonr@stolaf.edu>]
Sent: Friday, September 24, 2010 2:42 PM
To: P.Canepa
Subject: xcrysden supercell

Piero,

I'm still trying to understand the supercell business. I see:

http://www.xcrysden.org/doc/crystal.html#__toc__14

Is this what you are talking about? I can't implement xCrysDen here, but I think I get the general idea. This seems to me to be more than just a "supercell" -- it's a selection of atoms within a certain bounding box defined using unit cell axes vectors: {2a, (a+b), c}

Certainly you could do that relatively easily in Jmol already, but it might not be obvious at first how to do that.


Is that the sort of thing you are after?

Really this should be very easy to do in Jmol right now, and if this is all you are after, we could certainly implement a new select WITHIN option for this.

In xcrysden, surely, the fractional coordinates don't change, do they?
How does this relate to your "export" idea. (Export to what, exactly, in what format?)

Bob

--
Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
http://www.stolaf.edu/people/hansonr
phone: 507-786-3107


If nature does not answer first what we want,
it is better to take what answer we get.

-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900



--
Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
http://www.stolaf.edu/people/hansonr
phone: 507-786-3107


If nature does not answer first what we want,
it is better to take what answer we get.

-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900



--
Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
http://www.stolaf.edu/people/hansonr
phone: 507-786-3107


If nature does not answer first what we want,
it is better to take what answer we get.

-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900