(no subject)

Hi Lammps-users,

I am working on a deposition model on a 4H-SiC substrate. I’m facing yet another problem while running my simulation with MEAM, the pressure of the system has increased abruptly to a very large value and when I’m using any of the ensembles, the simulation stops and a non-numeric pressure error is occurring. I’m looking on how to resolve this issue. Please help me with this.

Here’s the simulation:

LAMMPS (31 Mar 2017)
Lattice spacing in x,y,z = 3.073 5.32259 10.053
Created orthogonal box = (0 0 3.41802) to (30.73 53.2259 100.53)
1 by 1 by 1 MPI processor grid
Created 1200 atoms
Reading potential file library.meam with DATE: 2012-06-29
Reading potential file SiC.meam with DATE: 2007-06-11
1200 atoms in group depo
400 atoms in group surface
400 atoms in group heat
400 atoms in group fix
1200 atoms in group Film
Changing box …
WARNING: Temperature for thermo pressure is not for group all (…/thermo.cpp:480)
Neighbor list info …
update every 1 steps, delay 10 steps, check yes
max neighbors/atom: 2000, page size: 100000
master list distance cutoff = 6
ghost atom cutoff = 6
binsize = 3, bins = 11 18 33
2 neighbor lists, perpetual/occasional/extra = 2 0 0
(1) pair meam, perpetual
attributes: full, newton on
pair build: full/bin/atomonly
stencil: full/bin/3d
bin: standard
(2) pair meam, perpetual, half/full from (1)
attributes: half, newton on
pair build: halffull/newton
stencil: none
bin: none
Setting up Verlet run …
Unit style : metal
Current step : 0
Time step : 0.001
Per MPI rank memory allocation (min/avg/max) = 10.63 | 10.63 | 10.63 Mbytes
Step Time Temp Press Lx Ly Lz
0 0 300 52337350 30.73 53.225921 97.112098
ERROR: Non-numeric pressure - simulation unstable (…/fix_nh.cpp:1029)
Last command: run 50000

P.S. : Thank you for solving my previous problem, I installed the MEAM package and it’s working now.


Ananya Singh

Dear T. Majdi,

Thank you for devoting time on my problem.

Earlier, I was also working with Tersoff potential for deposition. There is no doubt that deposition occurs but after deposition when I try to stabilize the final deposited structure, I am not able to obtain a layered/ordered structure. Also, I read in some research paper that the Tersoff potential produces amorphous structure and I wish to obtain an ordered one. For that reason, I installed MEAM package as it is said to produce layered structures.

The research paper that I am following uses MEAM potential, and they are getting crystalline structures after deposition. How is it possible? I am not able to figure out which factor I’m missing. Your help would be a great support.

Additionally, will SW potential result into ordered structures on stabilization after deposition?

Thank you


Ananya Singh

Dear Ananya,

I’m not particularly familiar with the MEAM potential. From what I understand, you can obtain ordered structures with any potential if it is correctly parameterized. If the article you are working based off is using your exact potential file and obtaining ordered structures then I think there may be a problem with one of the following:

  • Energy of incident atoms

  • Temperature of the substrate you are depositing on

  • Deposition rate (needs to be suitably low)

If these parameters are fine then perhaps using a smaller time step may help. I use 0.0004-0.0008 ps.

I follow the work of Dr. Zhou and his colleagues regarding thin film deposition. He has written some excellent manuscripts and has studied the effect of the various deposition parameters. Here are his relevant articles:



In his 2012 article he developed a bond order potential for depositing CdTe and in his 2013 he developed a SW potential for depositing CdTe and other materials. I’m copying an important description he gives in his 2012 article. I hope this helps!

"… past MD vapor deposition
simulations of semiconductors have used predominantly
Stillinger–Weber potentials. While Stillinger–Weber poten-
tials can be readily parameterized to ensure the lowest energy
tetrahedral crystal (e.g. diamond) and therefore the crystalline
growth of such a crystal, they do not capture the property
trends of other configurations encountered during growth. As
a result, these simulations are incapable of predicting accurate
defect structures. Tersoff potentials, which can improve over
Stillinger–Weber potentials in predicting property trends of
different configurations, are difficult to parameterize to ensure
the lowest energy for the equilibrium structure. As a result
of poor parameterizations, many literature Tersoff potentials
incorrectly predict amorphous growth. "

Best wishes,