3. Compute methane loading for one MOF

The average loading of the MOF at a given pressure will be computed using grand-canonical Monte Carlo (GCMC) simulations with the RASPA code.

  • The RASPA code needs several input parameters, some of which you will need to figure out

    parameters = ParameterData(dict={
        "GeneralSettings": {
            "SimulationType"               : "MonteCarlo",
            "NumberOfCycles"               : 2000,
            "NumberOfInitializationCycles" : 2000,
            "PrintEvery"                   : 2000,
            "ChargeMethod"                 : "Ewald",
            "CutOff"                       : 12.0,
            "Forcefield"                   : "<string>",
            "EwaldPrecision"               : 1e-6,
            "Framework"                    : 0,
            "UnitCells"                    : "<int> <int> <int>",
            "HeliumVoidFraction"           : 0.0,
            "ExternalTemperature"          : <float (Kelvin)>,
            "ExternalPressure"             : <float (Pascal)>,
        "Component": [{
            "MoleculeName"                 : "methane"
            "MoleculeDefinition"           : "TraPPE",
            "TranslationProbability"       : 0.5,
            "ReinsertionProbability"       : 0.5,
            "SwapProbability"              : 1.0,
            "CreateNumberOfMolecules"      :0,
    • Our simulations are performed under periodic boundary conditions. This means, we need to make our simulation cell large enough that a molecule will never interact with a two periodic copies of any of its neighbors. Given the cutoff radius of \(12\) Angstroms, how often do you need to replicate the unit cell of the material?

      Hint: The CIF files include information on the size of the unit cell.

    • To make things more interesting, we are going to use different force fields. Ask your instructor to give you a force field identifier.

  • You already performed a small GCMC calculation at 10 bar during the tutorial. Adapt the input file to your needs and run the calculation. Hint: Once running, the calculation should finish within 5 minutes.