Hello Lammps-users,
I am facing some problems with the deposition of Si and C on SiC.
Firstly, it is not equilibrating properly with pps, what minimization parameters should I use to obtain a completely relaxed structure?
This is the command I am using:
fix 1 all box/relax x 0.0 y 0.0 z 0.0 vmax 0.0005
min_style cg
min_modify dmax 0.5
minimize 1.0e-30 1.0e-30 100000 100000
Secondly, when I am depositing atoms, the temperature is suddenly dropping to zero.
This is what is happening:
Step atoms temp press pe ke etotal
434000 1317 2517.3257 58983.326 -3.7866521 0.19740814 -3.589244
434500 1317 2429.0814 59003.337 -3.7911558 0.19048804 -3.6006677
435000 1318 2473.1946 58894.028 -3.7754933 0.19380024 -3.5816931
435500 1318 2275.6262 58473.64 -3.7910645 0.17831871 -3.6127458
436000 1319 2456.9553 59155.425 -3.7786001 0.19238175 -3.5862183
436500 1319 2304.5649 58688.996 -3.7871849 0.18044945 -3.6067355
437000 1320 2473.0001 58798.11 -3.7820481 0.19349138 -3.5885567
437500 1320 2419.5468 58787.375 -3.7763062 0.18930911 -3.5869971
438000 1321 2440.7364 58649.97 -3.7796339 0.19082246 -3.5888114
438500 1321 2474.6758 59190.692 -3.7707757 0.19347592 -3.5772998
439000 1320 0 15360457 383.9492 0 383.9492
439500 1320 0 15332358 382.89594 0 382.89594
440000 1321 0 15325569 382.30368 0 382.30368
440500 1321 0 15324020 382.24901 0 382.24901
441000 1322 0 15323362 381.94065 0 381.94065
441500 1322 0 15322939 381.92862 0 381.92862
I used velocity command to reach 50K, then I used nvt ensemble to ramp the system from 50K to 2400K (it is my deposition temperature) and then I annealed it at 2400K after which I started with deposition. What is wrong with my script?
Kindly help me with this.
In anticipation of your reply,
Ananya Singh
Hello Lammps-users,
I am facing some problems with the deposition of Si and C on SiC.
Firstly, it is not equilibrating properly with pps, what minimization
parameters should I use to obtain a completely relaxed structure?
what do you mean by "completely relaxed" and how do you determine that?
please note, that a minimizer will steer a system to the next viable
minimum, which may not be the global minimum. that is a common property.
finding the global minimum of a many-particle system is a very non-trivial
task except in a select few high-symmetry cases.
This is the command I am using:
fix 1 all box/relax x 0.0 y 0.0 z 0.0 vmax 0.0005
min_style cg
min_modify dmax 0.5
minimize 1.0e-30 1.0e-30 100000 100000
Secondly, when I am depositing atoms, the temperature is suddenly dropping
to zero.
This is what is happening:
Step atoms temp press pe
ke etotal
434000 1317 2517.3257 58983.326 -3.7866521 0.19740814
-3.589244
434500 1317 2429.0814 59003.337 -3.7911558 0.19048804
-3.6006677
435000 1318 2473.1946 58894.028 -3.7754933 0.19380024
-3.5816931
435500 1318 2275.6262 58473.64 -3.7910645 0.17831871
-3.6127458
436000 1319 2456.9553 59155.425 -3.7786001 0.19238175
-3.5862183
436500 1319 2304.5649 58688.996 -3.7871849 0.18044945
-3.6067355
437000 1320 2473.0001 58798.11 -3.7820481 0.19349138
-3.5885567
437500 1320 2419.5468 58787.375 -3.7763062 0.18930911
-3.5869971
438000 1321 2440.7364 58649.97 -3.7796339 0.19082246
-3.5888114
438500 1321 2474.6758 59190.692 -3.7707757 0.19347592
-3.5772998
439000 1320 0 15360457 383.9492 0
383.9492
439500 1320 0 15332358 382.89594 0
382.89594
440000 1321 0 15325569 382.30368 0
382.30368
440500 1321 0 15324020 382.24901 0
382.24901
441000 1322 0 15323362 381.94065 0
381.94065
441500 1322 0 15322939 381.92862 0
381.92862
I used velocity command to reach 50K, then I used nvt ensemble to ramp the
system from 50K to 2400K (it is my deposition temperature) and then I
annealed it at 2400K after which I started with deposition. What is wrong
with my script?
how can anybody know? mind reading?? you are only providing some
extremely vague description.
have you visualized your system to see what is happening?
it is very suspicious, that you are losing an atom between steps 438500 and
439500.
axel.
Dear Axel,
Actually, I am performing deposition of Si and C atoms on a SiC substrate after which I need to form an equilibrated structure to analyze the formation of different polytypes of SiC and see its effects after changing some parameters mentioned in the attached research paper.
I have reviewed my script many times and tried each and every possible combination to remove this error. I am attaching the research paper I am following, my lammps script and log.lammps files with this mail. Kindly find the attachments.
Here are the list of problems I am facing:
-
In the research paper I am following, they have described a table( Table 5 ) in which they have specified the lattice parameters obtained after using MEAM potential,Tersoff potential, etc. and with MEAM potential, they are getting a=3.063 and c=10.020 lattice parameter where a=3.073 and c=10.053 is the experimental value and they are using 2d boundary condition. So, to incorporate all of these parameters, I am using pps boundary condition but the lattice parameters I am getting are 4.498 instead of 3.063 while c (z-direction ) is starting 5.67 instead of 10.053 (please refer to log(PPS).lammps for this. While with ppp, I am getting quite precise values but they(in research paper) are using 2-d periodic boundary condition.
-
They haven’t specified any ensemble they are using for increasing the temperature but after reading 7-8 research papers related to deposition, I decided to use nvt ensemble but when the deposition starts, the temperature drops to zero causing the velocity of ad-atoms to fall to zero(in case of ppf and ppp). This problem was not happening while tersoff potential. Am I missing something while calling this potential file? Are there some parameters which need to be specified for using this potential?
-
While using pps, deposition is not happening as there is an error which says deposition region extends outside the simulation box
Regards,
Ananya Singh
[in.finalSiC(pps)|attachment](upload://uZ6HdPtQrDGjXVvgr8OuU1mobXz.finalSiC§ (4.6 KB)
log(PPS).lammps (77.9 KB)
Governing factors for the formation of 4H or 6H-SiC.pdf (9.78 MB)
log(PPP).lammps (475 KB)
[in.finalSiC(ppp)|attachment](upload://8xB7Sw6pg702wntPqz6zR1WT1vX.finalSiC§ (4.59 KB)
Dear Axel,
Actually, I am performing deposition of Si and C atoms on a SiC substrate
after which I need to form an equilibrated structure to analyze the
formation of different polytypes of SiC and see its effects after changing
some parameters mentioned in the attached research paper.
please understand, that i don't have time to study and review your
research. that is your job or - at best - the job of your adviser. if you
have trouble understanding what is going on, simplify your simulation until
you do understand everything and then add the skipped pieces back,
one-by-one and study carefully what is happening.
i also notice, that you are asking more questions, but have failed to
answer mine.
what is happening in point 3 is *very* self-evident. you cannot maintain an
vacuum region with shrinkwrap (s) boundaries, it will *immediately*
collapse due to lack of atoms in them. you need to use shrinkwrap with
minimum (m) instead for that purpose.
axel.