# Out of range atoms when fix nvt + fic gcmc

(1 yes, set M=0
fix ID group-ID gcmc N X M …
X = average number of GCMC exchanges to attempt every N step (add and delete process)
M = average number of MC moves to attempt every N steps (mc move process)
(2 doesn’t matter fix nvt is before or after. only depend on where you put ‘run’

1. fix 1 all nvt …
2. fix 2 yourgas gcmc N X 0 …
3. run 100000
1,2,3 or 2,1,3: 1,2 run simultaneously;
1,3,2: only run 1;
2,3,1: only run 2.
(3 Usually, when the number of gas molecules is varying in a narrow range, it could be regarded as equilibrium. you should read more paper to find out how others dealing with this changing character statistically.

I just use the lammps mail list recently, so I don’t quite understand how to use it, but I have so many urgent problems to solve. Please forgive me. I have read a lot paper about adsorption using GCMC. They just mention how many steps to equilibrium and how many steps to average, but not mention how to deal with the changing character statistically in detail. I am using the fix ave/time command to average the excess amount. And now the problem I am facing is that the temperature of the system fall to zero suddenly, I think this is unnormal. So many difficulties make me feel helpless. Can you give me more advice ? I attach my input script and the output file. Your help is much appreciated.

Yours

Sincerely

600kpa.out (73.8 KB)

in.600kpa_363K (5.48 KB)

temperature is a representation of the velocity of particles, which means your gas particles were not moving or no gas is in the system.
this is mailing list is built for dealing with technical problems. if no error or warning was reported in your simulation, it’s then your own to think about. Did you use suitable chemical potential? did the parameters of force field been rightly written? balabala…
those are problems related to your understanding of a certain system, which your tutor get you to do. I’m not a specialist in gcmc. I only know how to get it running in lammps. You should talk to your advisor more often. the knowledge of molecule simulation is not a skill that can be learned in a short time.

OK, many thanks for your response. I think we can talk more on other platform if you are Chinese. Can you give me your contact like QQ? I have a lot problems on molecule simulation, but my tutor can’t help me because of some reasons. I am willing to do everything in return.

Indeed. The only tip I can give in addition to Mengzi’s is to try and make your input simpler: Start with just NVE to make sure your system conserves total energy first. Then use NVT and see if your system stays stably (fluctuates about the right average) at the right temperature. Only after that I would try to add GCMC into the mix.