Dear lammps users.
I want to estimate the amount of liquid in the pores at 100% relative humidity at any temperature.
Therefore, using the gcmc command, we are first trying to calculate the chemical potential of water vapor at 100% relative humidity.
A data file is created by inserting water molecules into the cell so that the relative humidity becomes 100% (temperature 80 ° C.)
In the input file I have written the following and made a test calculation.
(not using fix nvt command)
please see some comments below. i am not at all an expert on GCMC, so i am focusing on unrelated issues and am copying aidan, who is more qualified to comment on fix gcmc specifically.
Dear lammps users.
I want to estimate the amount of liquid in the pores at 100% relative humidity at any temperature.
Therefore, using the gcmc command, we are first trying to calculate the chemical potential of water vapor at 100% relative humidity.A data file is created by inserting water molecules into the cell so that the relative humidity becomes 100% (temperature 80 ° C.)
In the input file I have written the following and made a test calculation.
(not using fix nvt command)
unit lj
kspace_style pppm 1e-4
pair_style lj/cut/coul/long 7.913730 11.303883
fix 3 water gcmc 10 100 100 0 3456543 0.70 12 36 -16.25 0.1 mol my_one_water maxangle 180 full_energy
run 1000
please note, that LAMMPS is an MD code and not particularly well suited doing MC moves only. specifically for molecules, i would also want to run time integration. without that, running fix gcmc only every 10th step doesn’t make much sense. also your cutoffs are extremely large for reduced units. since you compare to real units why not use real units in LAMMPS as well, that would eliminate problems from unit conversions.
etc
It was confirmed that the number of particles changed, and on average it was the same as the number of particles inserted. I would like to ask 4 questions.
- Calculating the chemical potential at 80 ° C. and 100% relative humidity using the ideal chemical potential definition at the following URL yielded mu = -11.29 (-47.23 kJ / mol).
http://lammps.sandia.gov/doc/fix_gcmc.htmlHowever, when actually calculating with mu = -11.29, the number of particles increased steadily.
When estimating the chemical potential, is there anything to consider?
impossible for me to say with so little information.
- Is it possible to output the profile of chemical potential mu?
I want to judge whether or not the set chemical potential has been reached.
i don’t understand the question. to my knowledge the chemical potential is an input parameter.
- Looking at the profile, kinetic energy and temperature change. I thought that movement of particles was not solved in GCMC. Is it OK to ignore these values?
not sure what you are asking here.
- GCMC was carried out using the structure calculated by MD. In the final record in MD
ecoul+elong = -39.866109
However, at the 0 step of GCMC
ecoul+elong = -3.59306
.
Why has the value deviated greatly?
(Other energy is nearly equal)
impossible to say without more information about your respective input files for both the original run and the restart.
axel.
Dear Axel
Thank you very much for your reply.
It may be said that I am wrong because I do GCMC calculation for the first time.
First, I describe input.file and output.file below
Input.file