how can i get the adsorption isotherm in lammps

Hi all,
recently, i am studying the gas(may be methane) adsorption in silica nanopore. I model the united-atom methane and the silica nanopore. But, when i want to study the adsorption between them, i have met some difficulties:
First, i notice that, many people said MD+GCMC needed in adsorption simulation. But, i don’t know what roles the MD and GCMC plays respectively in the adsorption simulation.
Second, i attempted three different simulation as following. I found that, when i performed the pure GCMC in my simulation, and i set the temperature to 300K, but, the results i got in ‘.out’ file is quite lower, alway 0~5k.When i performed nvt+gcmc, the temperaturn in output i got was still lower.When i perfomed npt+gcmc+npt, the temperature i got in out file seem right, about 300K.When i performed nvt + gcmc, and i added some commands, the temperature i got is 300 in 100 step, but after that, an error occured:“ERROR: Computed temperature for fix temp/rescale cannot be 0.0 (…/fix_temp_rescale.cpp:145)”.
The input and out files as below.

Third, my attempting simulation is so slow, a pure gcmc simulation done need about 5 days using 4 processor,.I want to know , if this is normal or it is my input error.

Last, when i get the output information, how can i judge the adsorption equilibrium? And, when i plot the adsorption isotherm, what value should i use? average amount of the gas molecule?
That’s all

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See my response to your later query. And congratulations on realizing that you needed to start by studying a simple example, before attempting to run your silica nanopore problem.