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.