[Pw_forum] Questions about the relax/vc-relax calculation

[Jian XU]

Dear Shuai:

I'm also a new learner.

As for your first question, my experience is 'relax' is not equal to
'vc-relax'.

For short, 'relax' only change the atomic position, while 'vc-relax' has a
variable unit cell as well as variable position.

So if you do scf calculations by modifying the lattice constant and obtain
the lattice constant with the lowest energy, in my opinion, vc-relax may be
get similar result while the initial lattice constant is closed to the real
one.

Rds.


*————*

徐健    Jian XU

Dr. Eng.
Department of Metallurgical Engineering
College of Materials Science and Engineering
Faculty of Engineering, Chongqing University
​


On Sun, Jun 1, 2014 at 12:22 PM, Shuai <zhao-shuai at edu.life.kyutech.ac.jp>
wrote:

>  Dear QE users,
>
> I am a new learner and I have two questions about the relax/vc-relax
> calculation.
>
> The first is that if I do scf calculations by modifying the lattice
> constant and I could obtain the lattice constant with the lowest energy.
> And then on this basis if I do a relax calculation (not vc-relax), does its
> work equal to that of vc-relax?
>
> The second one is about the vc-relax calculation. After got the vc-relax
> result, I could find the new cell_parameters and atomic positions from the
> *vc-relax.out*. Thus do I need to set the new cell_parameters and atomic
> positions as the new parameters in the file of *nscf.in <http://nscf.in>*?
> or maybe the nscf calculation can read the cell_parameters and atomic
> positions automatically from the vc-relax.out?
>
> Thanks in advance.
>
> Best regards,
>
> Shuai
>
> --
> *Graduate School of Life Science and Systems Engineering*
> *Kyushu Institute of Technolog, Japan*
>
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