[Wien] Murnaghan equation

[Santhy Jaiker]

thank you stefaan.
  I will work out and tell you.
  
Stefaan Cottenier <Stefaan.Cottenier at fys.kuleuven.be> wrote:
  
> I am optimizing the volume of a hexagonal cell. I changed the 
> volume -9 to 0% reduction with step of -1 in optimize.job. I got 
> the smooth parabola. The minimum energy lies close to the volume of 
> -5% reduction. Volume at -5% reduction is V=999.6100. In Murnaghan 
> equation, minimum energy volume Vo=990.8361. I read your reply 
> about murnaghan question in 
> http://zeus.theochem.tuwien.ac.at/pipermail/wien/2006-November/008287.html.
> So Murnaghan equation gives minimum energy volume correctly.
> But after that i want to optimize c/a ratio. I had chosen the the 
> case_vol__-5.0.struct file to undergo change in c/a ratio at 
> constant volume. Because i don't have the struct file for volume Vo 
> showed by Murnaghan equation.
> am i in correct direction?

Nothing prevents you from making a case.struct with the optimal volume 
and same c/a as your initial series, and start the c/a optimization 
from there on. Once found the optimal c/a at that volume, make again a 
cell with that optimal c/a, and optimize the volume again, etc. etc., 
until nothing changes any more (often 2 such iterations are sufficient).

Alternative: optimize the volume for e.g. 5 different c/a ratio's, and 
determine the absolute minimum in an Energy versus (volume, c/a) plot 
(3D plot).

Stefaan



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Regards,
  Santhy Jaiker
   
  Research Scholar,
  Materials Thermodynamics Lab,
  Department of Metallurgical and Materials Engineering,
  Indian Institute of Technology Madras,
  Chennai - 600 036,  India
  Tel: 91-044-22575763
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