[Wien] How to fit birch Murnaghan EOS for the orthorhombic case

[delamora]

In the first case you have to do several calculations, in the option 6 you have 3x3x3 mesh and if you fit a 3D 2nd degree equation you get the answer with one, although long, calculation

f=a+bx+cy+dz+exy...

and the minimum will get you the optimized cell parapeters

Is this the most exact answer? I do not know, because you are fitting a parabola


Saludos


Pablo


________________________________
De: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> en nombre de BUSHRA SABIR <b_sabir437 at yahoo.com>
Enviado: sábado, 20 de mayo de 2017 03:52:53 p. m.
Para: wien at zeus.theochem.tuwien.ac.at
Asunto: [Wien] How to fit birch Murnaghan EOS for the orthorhombic case

Dear Wien2k users,

For an orthorhombic optimization case I have two queries:

I found two processes to optimize the orthorhombic structure 1. By Prof. Marks<http://www.google.com/url?q=http%3A%2F%2Fwww.mail-archive.com%2Fwien%40zeus.theochem.tuwien.ac.at%2Fmsg06932.html&sa=D&sntz=1&usg=AFQjCNGCMKrz7JWsrLLdCzs_cFgzw3v7dQ>  2. By Dr. Delamora<http://www.google.com/url?q=http%3A%2F%2Fwww.mail-archive.com%2Fwien%40zeus.theochem.tuwien.ac.at%2Fmsg10846.html&sa=D&sntz=1&usg=AFQjCNGASOL4Qw0CGGsITQZQUKxbn_SPBg>

To optimize the structure file according to the method suggested by Prof. Marks, I followed the below steps:

1. Vol optimization with option 1 in "x optimize" script. It will give optimized volume.
2. Using previously optimized structure, I will do here c/a optimization with option 3 from "x optimize". It will give us scaling for c/a. Updated c/a in the structure file obtained from this step and
3.  Using previously optimized structure, I will do here b/a A  optimization with option 4 from "x optimize". It will give us scaling for b/a. Used optimized b/a from here in the structure file obtained from this step after a fit.

Now my first Query is:
A. Is the final structure file (from step 3) is the well optimised for orthorhombic case?
B. Is this correct that the last step will give me a  fitted birch Murnaghan EOS?

For the process mentioned in "x optimize" with option 6 bu Delamora<http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10846.html>:


In the option 6 you can put one of the mentioned numbers
10, 27, 64,125 in which the parameters are varied by 3x3x3 (=27 different cases)  'a' is varied by -3 0 3, the same for 'b and 'c',

 then you have to fit a curve to these results


My second query is:

Is the fitting process is same for option 6 as for option 2 or 3 or we need to follow different approach?


Your help will definetly help us to shortout the problem.


Looking forward to hearing from you.


Regards


[http://mail.yimg.com/us.yimg.com/i/mesg/tsmileys2/01.gif]
________________________________
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20170521/41582fdb/attachment.html>