[Pw_forum] Fw: defect formation energy

[marsamos at democritos.it]

I think that calculations relaxing the volume should give defect 
formation enthalpy. But I always saw people fixing the defective cell 
to its original volume, as in general one is interested in low defect 
concentration and the elastic field created by the defect is larger 
than the simulation cell --> giving rise to a too large variation in 
the volume.

Quoting Duy Le <ttduyle at gmail.com>:

> if the defect concentration is too hight, when you do vc-relax the lattice
> parameter will be re-optimized. In reality, the defect concentration is
> about zero.
>
> On Fri, Sep 18, 2009 at 8:43 AM, xirainbow <nkxirainbow at gmail.com> wrote:
>
>> Dear:
>>
>> When you calculate without vc-relax, you deal with a point defect.
>> When you use vc-relax, you change the crystal parameters. That is to say,
>> you deal with a new kind of crystal, not a point defect.
>> It is just my own point of view ??
>>
>>
>>
>>>
>>> Ali Kazempour
>>> Physics department, Isfahan University of Technology
>>> 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
>>> Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>>>
>>> --- On *Fri, 9/18/09, ali kazempour <kazempoor2000 at yahoo.com>* wrote:
>>>
>>>
>>> From: ali kazempour <kazempoor2000 at yahoo.com>
>>> Subject: defect formation energy
>>> To: forum at democritos.it
>>> Date: Friday, September 18, 2009, 5:31 AM
>>>
>>>
>>> Hi
>>> for study of point defect ,  i do relax calculation and obtain positive
>>> defect formation energy while by vc-relax i gain negative. ?
>>> what is the difference between positive and negative formation energy?
>>> waht is the physical reasons?
>>> thanks a lot
>>> Ali Kazempour
>>> Physics department, Isfahan University of Technology
>>> 84156 Isfahan, Iran. Tel-1: +98 311 391 3733
>>> Fax: +98 311 391 2376 Tel-2: +98 311 391 2375
>>>
>>>
>>
>>
>> --
>> ____________________________________
>> Hui Wang
>> School of physics, Nankai University, Tianjin, China
>>
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>>
>
>
> --
> --------------------------------------------------
> Duy Le
> PhD Student
> Department of Physics
> University of Central Florida.
>



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