[Wien] minimizing atomic positions and lattice constants simultaneously

[Laurence Marks]

I think you have used a slightly long approach, and unless there is a
typo error you have not done it quite right. Let's step back for a
moment and think about the problem.

For an orthorhombic cell (or did you mean tetragonal) a,b & c are all
different. What you want to find is the minimum in the energy as a
function of these three, E(a,b,c). Note, if tetragonal then it is just
E(a,c) or E(a/c,V).

Normally the largest change is with volume, so provided that the
ratio's a/c and a/b are not very wrong you would optimize this first,
then optimize the ratio's next. The volume would be option 1 in "x
optimize". You could then do option 3 or 4 for each volume (vary c/a
or b/a) although it is probably best to find the optimum volume first
then use these. There are some tools for this in the web interface,
although I almost always end up doing a simple fit with Excel.

An alternative is to go directly to option 6 in "x optimize".

If you have a tetragonal cell, you can take all the data you have and
do a 2D fit to find the minimum energy. Again, there are some tools or
you can use Excel. If it is orthorhombic then your step (3) was not
write and you have not varied a/b yet and need to.

Think about it a bit, it will become clearer.

On Mon, Jul 16, 2012 at 6:40 AM, Pradeep Kumar
<pradeep.tachyons at gmail.com> wrote:
> Dear Prof. Marks & Wien2k users,
>
> I am very new user of wien2k (version 11.1) just started work about a
> month back and this is my first mail in this archive.........
>
> I want to perform optimization of lattice constant and atomic
> positions simultaneously for an orthorhombic compound. I have gone
> through Optimization notes by L. D. Marks and as per I understand
> notes, I did following steps:
>
> (1) Calculate the total energy for 5 different volumes with fixed
> A:B:C ratio, and optimize the internal coordinates for each volume.
>
> (2) For each volumes, calculate the energy of five different c/a
> ratios and optimize the internal coordinates for each c/a ratio.
>
> (3) For each c/a ratios, calculate the total energy for five different
> volumes with fixed A:B:C ratio and optimize the internal coordinates
> for each volume.
>
> (4) Finally I have 5 volume directory and in each directories, I have
> 5 directories of c/a ratios with optimized internal positions (each
> with a set of 5 volumes )
>
> now my question is:  which file will give me optimized lattice
> constant and atomic positions both.
>
> Thanks in advance.
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 1-847-491-3996
"Research is to see what everybody else has seen, and to think what
nobody else has thought"
Albert Szent-Gyorgi