LAMMPS WWW Site - LAMMPS Documentation - LAMMPS Mailing List Archives
Re: [lammps-users] Simulation of Si3N4
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [lammps-users] Simulation of Si3N4


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 18 Dec 2017 15:23:53 -0500

you seem to be deforming in z direction, yet your system is extremely shallow in z. i would suggest to check, if your result is dependent on the thickness of your system in z.

axel.

On Sun, Dec 17, 2017 at 8:06 PM, Khourshaei Shar, Ali <akhoursh@...6666...> wrote:

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 crystallography.net 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 Input.in 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,

Ali


[1] http://pubs.acs.org/doi/abs/10.1021/jz4007977


From: Axel Kohlmeyer <akohlmey@...24...>
Sent: Sunday, December 17, 2017 7:35:19 PM
To: Khourshaei Shar, Ali
Cc: lammps-users@...396...sourceforge.net
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.

axel.

 

Sincerely,

Ali


------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
lammps-users mailing list
lammps-users@...655....net
https://lists.sourceforge.net/lists/listinfo/lammps-users




--
Dr. Axel Kohlmeyer  akohlmey@...12...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
lammps-users mailing list
lammps-users@...6297....sourceforge.net
https://lists.sourceforge.net/lists/listinfo/lammps-users




--
Dr. Axel Kohlmeyer  akohlmey@...12...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.