[Wien] RMT choice and cell size

[Chandrika]

Dear Marks,
Thanks for the information and thanks also for a very good manual for 
beginners.
Just another question : Is there a 'rule of thumb' about how much smaller 
than covalent/atomic radius the RMT should generally be. How do you say that 
1.8 would be too big RMT for SiC?
Thank you once again,
Best wishes,
Chandrika
----- Original Message ----- 
From: "L. D. Marks" <L-marks at northwestern.edu>
To: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
Sent: Monday, March 20, 2006 5:35 AM
Subject: Re: [Wien] RMT choice and cell size


> 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".
> -----------------------------------------------
> Laurence Marks
> Department of Materials Science and Engineering
> MSE Rm 2036 Cook Hall
> 2220 N Campus Drive
> Northwestern University
> Evanston, IL 60201, USA
> Tel: (847) 491-3996 Fax: (847) 491-7820
> email: L-marks at northwestern dot edu
> http://www.numis.northwestern.edu
> -----------------------------------------------
>
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