[Wien] [Wien2k User Group] Volume optimization of Zirconium

[Stefaan Cottenier]

If this is the entire content of your case.outputeos:

 > Vol 	energy 	de(Birch-Murnaghan) Pressure
 > 314.2133 -14396.851	0.009235	-1.432
 > 314.2133 -14396.848	0.005909 -1.432

then you are make a eos fit through 1 single E(V) point... (actually 
through two, but they are the same). This doesn't make sense, as there 
are 4 free parameters in this eos. That's why you find very much rounded 
values for B and BP:

 > V0 B(GPa) BP EO
 > 309.5778 100.0000 5.000 -14396.842

(100 and 5, they are probably just the defaults).

Make your eos fit trhough at least 4 data points (5-10 is better). They 
should all be listed as (:VOL, :ENE) in case.vol.

Negative pressures correspond to volumes larger than the equilibrium volume.

Stefaan



Ghosh SUDDHASATTWA wrote:
> Dear Micheal,
>  As suggested, I did the volume optimization with -5% to +5% 
> The values are as shown for alpha-zirconium. 
> V0 B(GPa) BP EO 
> 309.5778 100.0000 5.000 -14396.842
> Vol 	energy 	de(Birch-Murnaghan) Pressure 
> 314.2133 -14396.851	0.009235	-1.432
> 314.2133 -14396.848	0.005909 -1.432
> ............................................................................
> ;
> Are these values possible. 
> I am really amazed to see the value of pressure which is negative!!!!
> The ground state energy is I guess -14396.842. Am I correct? 
> With spin orbit coupling, the ENE value was -14396.892 which are pretty
> close.
> 
> Then why these pressure values are negative. 
> I seek one more clarification. 
> In the energy plot curve option, there comes "by using "*". Scf files. 
> If we want to select a few files and not all the files for plotting, then do
> we have to enter the file names with commas separating them? 
> I ask this question because the points from the previous volume optimization
> also are coming in the current plot. 
> 
> Thanks 
> Suddhasattwa Ghosh 
> 
> 
> -----Original Message-----
> From: wien-bounces at zeus.theochem.tuwien.ac.at
> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Michael
> Fischer
> Sent: Sunday, January 10, 2010 3:44 AM
> To: wien at zeus.theochem.tuwien.ac.at
> Subject: Re: [Wien] [Wien2k User Group] Volume optimization of Zirconium
> 
> Hello,
> 
> I can only guess on this problem, but I am quite sure that changes of 
> the c/a ratio from -25% to +25% are much too large, since this probably 
> leads to an overlap of the RMT spheres.
> Try a set of calculations for smaller changes of the c/a ratio, e.g. 
> from -5% to +5%, and make sure beforehand that the RMT spheres do not 
> overlap in the most strongly distorted structures.
> 
> Regards
> Michael
> 
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-- 
Stefaan Cottenier
Center for Molecular Modeling (CMM)
Ghent University
Technologiepark 903 (2nd floor)
BE-9052 Zwijnaarde
Belgium

http://molmod.Ugent.be
email: Stefaan . Cottenier /at/ UGent . be