Viscosity Calculations with Hybrid Particle-Field Molecular Dynamics Simulations

Area of Science:

• Computational physics
• Fluid dynamics
• Molecular dynamics simulations

Background:

• Hybrid particle-field (HPF) molecular dynamics (MD) simulations can exhibit artifacts in nonequilibrium shear flow due to the absence of explicit particle collisions.
• These artifacts lead to nonlinear velocity profiles, limiting the accuracy of traditional HPF methods.

Purpose of the Study:

• To address the limitations of HPF simulations by integrating multiparticle collision dynamics (MPCD).
• To accurately calculate fluid viscosities and investigate the performance of the combined HPF-MPCD method.

Main Methods:

• Hybrid particle-field (HPF) molecular dynamics simulations were combined with multiparticle collision dynamics (MPCD).
• Nonequilibrium MD simulations of shear flow were performed to analyze velocity profiles and viscosity.
• The MPCD collision period (Tcol) was tuned to adjust fluid viscosity.
• Momentum conservation was analyzed using 8-point central difference gradient interpolation.

Main Results:

• The integration of MPCD into HPF successfully mimicked collision dynamics, yielding linear velocity profiles comparable to Lennard-Jones (LJ) simulations.
• A general equation for viscosity (η(ρ, T)) was derived, showing a weaker dependence on temperature and density for HPF-MPCD systems compared to LJ fluids.
• HPF and HPF-MPCD methods demonstrated significant computational efficiency, achieving up to 3 orders of magnitude faster simulations than traditional MD.
• The 8-point central difference gradient interpolation method proved superior in accuracy and stability for momentum conservation.

Conclusions:

• The HPF-MPCD method accurately calculates fluid viscosities and overcomes artifacts present in standard HPF simulations.
• This approach offers a scalable, versatile, and computationally efficient alternative to traditional MD for simulating complex fluid systems.
• The findings highlight the potential of HPF-MPCD for large-scale, high-sampling simulations in fluid dynamics.