[Wien] volume_optimization

[Peter Blaha]

Well, I would say it is UNUSUAL that theory is wrong by 20 %, although 
we know that such cases may occur (van der waals bonds).

But TiC MUST NOT differ by such a large amount. You are doing something 
wrong.

Torsten Andersen schrieb:
> Dear Mr. Thapa,
> 
> it is not unusual that the theoretical lattice constant differs by 20% 
> with respect to the experimental one. You should try different 
> XC-Potentials in order to see which one comes closest.
> 
> For (ii) and (iii), the lattice constants in the Wien code are the ones 
> in the unit cell, so there is usually direct correspondence to experiment.
> 
> Best regards,
> Torsten Andersen.
> 
> 
> RK_Thapa wrote:
>> Dear S. Cottenier,
>> I have a question with regard to lattice constant by volume optimization.
>> (i) For TiC case, experimental a=3.328Ang, whereas by volume optimisation it comes out quite different like a=2.734 Ang.
>> (ii) Is it that we have to divide by 4 the volume obtained by volume_optimization as it TiC is a FCC structure.
>> (iii) Similarly, the case of BCC crystals, we  must divide volume by 2, then we are getting the correct value of theoretical lattice constant.
>> Requesting you to answer me please. Sorry for the simple question and doubt.
>> Regards,
>> R.K.Thapa
>> Mizoram,India
>>
>>
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> 

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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