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[lammps-users] Simulation of Si3N4
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[lammps-users] Simulation of Si3N4

From: "Khourshaei Shar, Ali" <akhoursh@...6666...>
Date: Mon, 18 Dec 2017 01:06:02 +0000

Hi Prof. Kohlmeyer,

I got your point and my apology for failing to elaborate appropriately on the problem. For potential, I used tersoff potential which was calibrated by Brito Mota. For the initial configuration, I downloaded the .Cif file of Beta silicon nitride from and also I built it using the space group and then I replicated it to obtain a thin layer ( ending in the same results for both cases ). For stress, I used virial and for strain,  it is engineering strain. I attached my files  ( Si3N4. in as my initial configuration and as my input command SiN as the parameters of tersoff potential). I also, attach the diagram I expect to get based on a published paper [1]. But, anyway the answer I get is not correct as I obtain a high value of fracture stress and even strain. I will deeply appreciate your help within any comment. Honestly, this is the problem that I'm working on it for a month. But, unfortunately I couldn't solve it and I really think that to the best of my knowledge I'm doing the simulation correctly.

Eagerly looking forward to hear back from you,

Kind regards,



From: Axel Kohlmeyer <akohlmey@...24...>
Sent: Sunday, December 17, 2017 7:35:19 PM
To: Khourshaei Shar, Ali
Subject: Re: [lammps-users] Simulation of Si3N4

On Sun, Dec 17, 2017 at 3:25 PM, Khourshaei Shar, Ali <akhoursh@...6666...> wrote:

Dear LAMMPS users,

I'm trying to simulate mechanical behavior of Beta silicon nitride thin layer in z direction. To gain that, I used the attached input files and I get the attached curve as stress -strain curve. However, the curve shouldn't be correct as Si3N4 is a brittle material and based on the literature we expect it to fail within 5% of strain and a stress below 20 GPa. So, I tried several possibilities. But, I couldn't solve the issue. Therefore, I wonder if you could please help me out. 

help you how?
you don't provide any tangible information to assess where any potential problems could be. there could be issues with the force field, issues with the geometry, issues with the workflow, issues with the choice of parameters, issues with the units, issues how you compute properties and so on.

thus one would need a well functioning crystal ball to provide meaningful help.
i've tried several times to request one from santa@...7292..., but apparently i seem to be stuck on the "naughty" list.
perhaps you can put in a good word for me.





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Dr. Axel Kohlmeyer  akohlmey@...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

Attachment: Stress - Strain.PNG
Description: Stress - Strain.PNG

Attachment: Stress - Strain ( Paper ).PNG
Description: Stress - Strain ( Paper ).PNG

Attachment: Input files.rar
Description: Input files.rar