[Wien] [Wien2k Users] Lattice Stability using Structure Optimization

[Stefaan Cottenier]

Now read Martins mail again, and consider what he writes about enlarging 
the lattice constants (i.e. increasing the volume of the cell). Then, 
ponder what it means that you have 2 degrees of freedom here: a and c, 
or alternatively, volume and c/a.

Stefaan


Ghosh SUDDHASATTWA wrote:
> Dear Martin, 
> Probably I am responding to your mail after a long time. And moreover, you
> are absolutely correct. 
> If Pu is imagined to be in the Zr atomic positions, it is very natural that
> the occupation of Pu would naturally increase the c/a ratio  and there is no
> meaning to do a structure optimization for cases like -2 % or -5 % change in
> c/a ratio. The equilibrium c/a would be somewhere around +12-15 % change
> (gross)  and this is what is expected from physics. 
> That is what I get from Wien2k 
> 
> Thanks Stefaan and Martin, 
> 
> 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 Martin Pieper
> Sent: Tuesday, March 02, 2010 6:32 PM
> To: A Mailing list for WIEN2k users
> Subject: Re: [Wien] [Wien2k Users] Lattice Stability using
> StructureOptimization
> 
> Dear Ghosh Suddhasattwa,
> 
> being a beginner with Wien2k myself and not having read your exchange with 
> Stefaan I probably should be quiet to avoid confusion but maybe its simple: 
> Did you adapt (enlargen) the lattice constant when you put in Pu instead of 
> Zr? I would expect that Pu needs a lot more space than Zr and, therefore,
> you 
> might simply be too far away from any reasonable lattice constant and far
> out 
> of the trial range of the optimization procedure...
> 
> Best regards,
> 
> Martin
> 
> 
> Am Montag, 8. März 2010 schrieb Ghosh SUDDHASATTWA:
>> Dear Dr.Stefaan,
>>
>> Coming back to the problem we discussed regarding lattice stability a few
>> days back, I have done a few things but am not able to proceed further.
>>
>> I imagine Pu in a Zr lattice (hcp, space group 194)
>>
>> There is only one equivalent position (0.3333333 0.666667 0.25)
>>
>> I replaced Zr atom with the Pu atom.
>>
>> My approach was the following
>>
>> 1.	Calculate ENE without spin orbit and with spin orbit
>> 2.	Structure optimization (Option 5)
>>
>>
>>
>> The ENE without spin orbit was -118767.962 Ry and with spin orbit was
>> -118769.097 Ry.
>>
>> I chose Option 5 for the structure optimization and it created 16
> different
>> struct files.
>>
>> Optimize.job was run and it did not give any errors. (Removed # from x
>> dstart only)
>>
>> When I chose energy vs volume in plot; it gave a linear variation and not
>> like what is given in the UG guide for TiC.
>>
>> Can you please tell me if I have done any mistake?
>>
>>
>>
>> Suddhasattwa Ghosh
> 
> 
> 


-- 
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