Molecular Dynamics Force-Field Refinement against Quasi-Elastic Neutron Scattering Data

Area of Science:

• Materials Science
• Computational Chemistry
• Condensed Matter Physics

Background:

• Quasi-elastic neutron scattering (QENS) probes dynamics at length and time scales relevant to molecular dynamics (MD) simulations.
• Current fitting methods rely on time-independent equilibrium measurements, limiting analysis of dynamic data.
• Bridging simulation and experimental dynamics data offers opportunities for enhanced model accuracy.

Purpose of the Study:

• Develop and validate an algorithm to fit simulation-derived incoherent dynamical structure factors against QENS data.
• Address challenges in fitting, including environmental disparities and simulation sampling limitations.
• Refine force-field parameters for molecular systems using experimental dynamics data.

Main Methods:

• Developed an algorithm to fit simulation-derived incoherent dynamical structure factors to QENS data.
• Applied the method to full-atom molecular dynamics simulations of octa-methyl polyhedral oligomeric silsesquioxane.
• Focused on refining the force-field parameter for methyl group rotation activation energy.

Main Results:

• Successfully fitted simulation data to experimental QENS data, probing diffusive dynamics.
• Overcame simulation-experiment environmental disparities and sampling limitations.
• Achieved a simulated activation energy within 5% of the experimentally derived value, well within experimental error.

Conclusions:

• The developed fitting method effectively refines force-field parameters by integrating simulation and QENS dynamics data.
• The methodology shows promise for analyzing other diffusive motions and systems, including coarse-grain models.
• The approach can be extended to coherent dynamic structure factors without additional complexity.