[Wien] RMT choice and cell size

[L. D. Marks]

Almost certainly your initial RMT's were too large; provided that the 
spheres do not overlap the dependence upon RMT's of lattice parameters is 
rather weak.

On Sat, 18 Mar 2006, Chandrika wrote:

> Hello Wien Users,
> In doing volume optimisations I found that derived cell dimensions are very sensitive to RMT. For example when I optimised the structure of a cubic SiC with RMT 1.8 I get optimised a,b,c ~ 4.1 A. When I reduced RMT to 1.4, I get optimised a, b, c ~3.6 A. This is a large change.
> My question is how small should one go with RMT reduction? How much smaller than the covalent radius can RMT go (Si = 1.1 A)? Do I keep reducing it till I get the lowest energy crystal size? I am interested in deriving total energy and cell diemnsions.
> I have read the Optimisation Notes  by Marks (highly useful) and the FAQ by Blaha but perhaps I have missed a point.
> Please suggest.
> Thank you in anticipation.
> Chandrika
>
> -----------------------------------------------------------------------------------------
> Dr (Ms) Chandrika Varadachari
> Raman Centre for Applied and Interdisciplinary Sciences
> 16A Jheel Road
> Calcutta 700075
> India
> Tel : 91-33-24830029
> Fax : 91-33-24180610
> web : www.rcais.org.in
>

Note: if you have an old email address for me, please note that "nwu" has
been changed to "northwestern".
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Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
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Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
http://www.numis.northwestern.edu
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