Modeling and simulation for ionic liquids in oil.

Molecular Dynamics (MD) simulation setup for modeling Ionic Liquids (ILs) in oil using LAMMPS. The code sets up a simulation where an IL (e.g., 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6]) is mixed with an oil molecule (e.g., hexane).

Prerequisites:

• Install LAMMPS (Download)

• Prepare IL and oil molecule force fields (e.g., OPLS-AA, GAFF)

LAMMPS Input Script

This script sets up a coarse-grained simulation of ILs in oil.

lammps

# LAMMPS Input File for Ionic Liquids in Oil Simulation

units real

atom_style full

boundary p p p

# Read initial structure file (ILs + oil molecules)

read_data ionic_liquid_oil.data

# Define force field (example: OPLS-AA)

pair_style lj/cut/coul/long 12.0

pair_modify mix arithmetic

bond_style harmonic

angle_style harmonic

dihedral_style opls

# Define Neighbor List

neighbor 2.0 bin

neigh_modify every 1 delay 0 check yes

# Define Electrostatic Solver (Ewald Summation)

kspace_style pppm 1.0e-4

# Set Temperature Control (NVT Ensemble)

fix 1 all nvt temp 300.0 300.0 100.0

# Compute Interfacial Properties

compute rdf all rdf 100

compute msd all msd

# Output Thermodynamic Data

thermo 1000

thermo_style custom step temp pe ke etotal press density

# Dump File for Visualization

dump 1 all atom 1000 dump.ionic_liquid_oil.lammpstrj

# Run Simulation

timestep 1.0

run 500000

Explanation:

1. System Setup:

   • Uses real units (suitable for molecular systems).

   • Periodic boundary conditions (p p p).

   • Reads molecular structure from ionic_liquid_oil.data.

2. Force Fields:

   • Uses Lennard-Jones & Coulomb interactions (lj/cut/coul/long).

   • Electrostatics handled with PPPM (Particle-Particle Particle-Mesh) solver.

3. Simulation Control:

   • Runs an NVT ensemble (constant temperature).

   • Uses Ewald summation for accurate electrostatics.

   • Computes radial distribution function (RDF) and mean square displacement (MSD).

4. Thermodynamics & Output:

   • Outputs temperature, energy, pressure, and density every 1000 steps.

   • Saves trajectory (dump.ionic_liquid_oil.lammpstrj) for visualization in VMD or OVITO.

Next Steps:

• Prepare Input Data (ionic_liquid_oil.data): Use Packmol or VMD to generate molecular coordinates.

• Run Simulation:

  lmp_stable -in ionic_liquid_oil.in

Analyze Results:

• RDF (compute rdf): Check IL-oil interactions.

• MSD (compute msd): Study IL diffusion in oil.