Before running GEMC adsorption simulations for a large number of nanoporous materials, the total number of adsorbate molecules for the simulations in each materials needs to be judiciously chosen. This is because a too small system size will deplete the vapor box, and a too large system size will result in large amounts of computation wasted in simulating the vapor box.

A rule of thumb is to make the vapor box length at least 30 angstroms at the lowest temperture and highest pressure. This can be done by

• Estimate the saturation loading either using a simulation with an ideal gas box at very high pressure and low temperature, or calculating from the pore volume (void fraction * unit cell volume * number of cells) of each zeolite and multiply it by the liquid density of the adsorbate.
• Add the number of ideal gas molecules at the lowest temperature and highest pressure in a 30-angstrom box to the saturation loading. This will become the total number of molecules for each material.

To generate the input files for all simulations in a farmed job, you will need to create the following "seed" files:

• A JSON configuration file jobdata.json specifying the zeolites, state points, and length for each job. An example jobdata.json file looks like below (note that JSON does not support comment, and the description after # is intended only for explanation in this document):

{
    "cif": "/home/siepmann/sun00032/simulations/pcod/cifs", # location of zeolite structures
    "ztb": "/home/siepmann/sun00032/simulations/pcod/ztb", # location of zeolite structuretabulated potentials
    "exe": "/home/siepmann/exe-farm/src/topmon 1 1 1", # path to MCCCS-MN executable, including job-farming command line arguments
    "zeolites": "../pcod.txt", # file to the list of zeolites
    "pressures": [0.100, 0.271, 0.739, 2.009, 3.00, 5.460, 14.840, 40.340], # list of all pressures
    "temperatures": [77.00, 92.40, 110.88, 133.06, 159.67, 191.60, 229.92, 275.90], # list of all temperatures
    "n_indep": 4, # number of independent simulation
    "t_init": 3, # total length of initialization (volume relaxation) in hours
    "t_equil": 24, # total length of equilibration in hours
    "t_prod": 24, # total length of production in hours
    "max_walltime": 6, # maximum length of each job
    "arch": "HPE" # HPC architecture to generate job script
}

• A JSON file ninit.json containing the number of molecules to be initialized for each zeolite. A example ninit.jsob file looks like below:

{
    "8056830": 1964,
    "8067418": 1357,
    "8078629": 1366,
    "8080784": 1154,
    ...
}

• A seed directory seed/ which contains the template input files of a simulation. The seed/ directory needs to contain two files at bare minimum: topmon.inp and fort.4.
  • The seed/topmon.inp file is usually a symbolic link to a master topmon.inp file in the root directory of the job. Then all topmon.inp files in the farmed simulations will be linked to the same master file.
  • The seed/fort.4 file will be copied and manipulated for each stage of the simulations.
• A text file containing the list of zeolites zeolite.txt is also usually created in the root directory.

Before generating input files for all simulations, the working directory will look like below:

.
├── jobdata.json
├── ninit.json
├── seed
│   ├── fort.4
│   └── topmon.inp
└── zeolites.txt

With a working directory with required files listed above, run

python /path/to/mcccs_proc/quickfarm/initialize.py

to create input files for all simulations. After running the initaialize.py script, the working directory will look like:

.
├── jobdata.json
├── ninit.json
├── job.sh # job submission script
├── jobs # job list file to be used by MCCCS-MN
│   └── run1.txt
├── seed
│   ├── fort.4
│   └── topmon.inp
├── simulations # directories containing simulation inputs
│   └── ...
├── test # test directory for dry run
│   └── ...
└── zeolites.txt

Before running the large farmed job by job.sh, it is recommended to first perform a sanity check using the sample files produced in the test/ directory to make sure there is no error in the simulation input files. To do this, simply run the MCCCS-MN job farming executable under the test/ directory with 2 processes:

cd test
mpirun -n 2 /path/to/MCCCS-MN/topmon 1 1 1
cd ..

A successful test is marked by MCCCS-MN exiting without any errors (exit code 0).

Then the farmed job can be submitted to the job scheduler of the HPC cluster:

sbatch job.sh

After a job is completed, use quickfarm/next.py to batch process all input files in a farmed job to the next round of simulations. Usage of the next.py script is:

python next.py [current_stage] [next_stage (optional)]

Choices of current_stage and next_stage arguments inlcude init, equil, and prod. When executing the script with only the first argument, the simulations of the farmed jobs will be kept in the same stage (initialization, equilibration or production), and the files generated from the last round will be stored in a directory named init-$x, equil-$x, or prod-$x, where $x will automatically increment if the simulations are kept in the same stage. When executing the script with two arguments, the simulations will be switched into the next stage, for example, from equilibration to production. The job count $x will be also restored to 1 for the next stage.

Before submitting a job after running next.py, make sure that the file jobs/done.txt does not exist. Otherwise the content in jobs/done.txt will be excluded in the next run.

After all simulations stages have completed, run next.py prod again to store the last round of simulation outputs into the prod-$x folder.

Simulation outputs can be collected using a custom script, the getData.py file in Rob DeJaco's MCFlow, or the readfort12/readfort12_mpi scripts provided by this repository.

To use readfort12 or readfort12_mpi, an additional file run.txt need to be created to specify the directories to collect data, then the executable is run in the root directory of the farmed job:

cp jobs/run1.txt runs.txt
mpirun -n 4 ./readfort12_mpi prod-1 prod-2 prod-3 [...]

The program will create a CSV file fort12.csv which contains ensemble averages for each simulation from the fort.12 output file.