[Pw_forum] PBC problems

毛飞 maofei at mail.bnu.edu.cn
Mon Dec 16 13:10:42 CET 2013

Hi, Julen


Hi, Julen


Thank you for your immediate reply. I think you remarks are very usefully to me.

I have another question about the PBC in bulk calculation. Sometimes the authors said, the PBC is used in their work, the supercell size (e.g. 4×4×4 supercell) is chosen so as to minimize the spurious effects of the repetition. 


I wondering that what is meaning of 4, does it mean 4 primitive cells? And what is the relationship between the supercell and the simulation box.


Thank you in advance.


发件人: "Julen Larrucea" <julenlist at gmail.com>
发送时间: 2013年12月16日 星期一
收件人: "PWSCF Forum" <pw_forum at pwscf.org>
主题: Re: [Pw_forum] PBC problems

Dear Evan,

leaving distance between a molecule and the boundary is normally used only for simulating isolated molecules, or surfaces (in order to simulate the vacuum on one of the sides of the crystal).

The point in using PBC in bulk, is that you can simulate an infinite system by only computing a few atoms, and therefore there should not be any gap at all.

A quick tip: you can use for example JMol for opening your pw.x output, and then in the terminal type:

open "pw_output_file" {3 3 3}

This will show you 3 replicas of your system on each direction, and if you want to simulate bulk, it should look uniform.

  Best regards


On Mon, Dec 16, 2013 at 12:00 PM, 毛飞 <maofei at mail.bnu.edu.cn> wrote:

Dear all


I have a general question about doing calculation with periodic boundary condition (PBC). When I simulate the bulk materials (e.g. crystals), if I have applied the PBC in 3 dimensions of the simulation box, do I have to give some margins between the considered system and the boundary of the simulation box? Or there should be no space between them, the system should connected with its images seamlessly. But usually, as said in some papers, in order the minimize the spurious interaction with its images, the distance between the considered system and the boundary of the simulation box should be large enough.


I am a little puzzled with this issue. Any comment is appreciated. Thank you in advance.



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Dr. Julen Larrucea
Postdoctoral researcher,
BCCMS, HMI Group, University of Bremen
Phone: +49 421 218 64582
Fax: +49 421 218 64599
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