[Pw_forum] Equation of state with PW.x

[GAO Zhe]

Dear Furman:
I think, the easier and better way to make such a "compress" is using isostatic pressure, which can be specified by parameter "press" in "cell" namelist, especially for the un-cubic system. For example, in HCP structure, the cell is determined by "a" and "a/c", while the volume changing, not only "a", but also "a/c" ratio changes, too.
Therefore, you can do a batch of "vc-relax" tasks with different press and gather the final volume and total energy to fit EOS. The aim compress, as 10% or 20% shrinkage, can be found from EOS fitting result, where you can obtain the P-V curve.


--
GAO Zhe
CMC Lab, Materials Science & Engineering Department,
Seoul National University, South Korea
 

At 2012-06-08 15:17:36,"David Furman" <sirok4 at gmail.com> wrote:


Hello dear users and developers,

 

I'm trying to calculate the equation of state of Europium oxide, but I have some doubts regarding my procedure.

I have the xyz coordinates of the unit cell in angstroms which I put into atom_positions and also define the needed celldm's().

 

I'm interested to compress the material to different values (say, 0%, 10% and 20% volumetric compression) and calculate the total energy each time.

 

Do I have to change the given initial xyz coordinates in atom_positions AND the celldm() , or just change the celldm() accordingly to the compression and pw.x will do the proper changes to the positions of the atoms ?

 

I have done some calculations with uncompressed unit cell and with 20% compressed unit cell (by changing to the proper compressed celldm() values) but the difference in energy was about 0.5 Ry which i believe to be quite small. (Of course I checked previously for convergence).

 

Am I doing it wrong ?

 

Any help will be greatly appreciated

 

David Furman, Graduate Student| Fritz Haber Research Center for

Molecular Dynamics, The Hebrew University of Jerusalem | +972-8656-8909

 
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