Bias-Deletion Metadynamics Revealing Volume-Rotation Coupling Mechanisms in Metal-Organic Frameworks

Area of Science:

• Computational Chemistry
• Materials Science

Background:

• Enhanced sampling methods in molecular dynamics simulations face challenges with interdependent modes in complex systems, leading to nonergodic behavior.
• Conventional methods often require complex collective variables and exhibit hysteresis or dependence on initial configurations.

Purpose of the Study:

• To introduce bias-deletion metadynamics, a novel technique for improved sampling in molecular dynamics.
• To enable systematic refinement of sampled configurational space and accurate free-energy surface recovery.

Main Methods:

• Bias-deletion metadynamics: a technique that conditionally deletes biases to allow repeated exploration of transition pathways.
• Benchmarking on alanine dipeptide to assess performance in recurrent rotational motion.
• Application to CAU-13 and a series of isoreticular metal-organic frameworks (MOFs) to resolve phase transitions and linker-framework coupling.

Main Results:

• Bias-deletion metadynamics successfully handles recurrent rotational motion, outperforming conventional metadynamics.
• The method resolves distinct phases of CAU-13 using only a volume bias.
• Intricate coupling between linker rotation and framework volume in MOFs (MIL-53(Al), NU-2002, MIL-cub, NU-2000) is uncovered, correlating linker dimensionality with volume-specific rotational preferences.

Conclusions:

• Bias-deletion metadynamics offers a robust approach for overcoming limitations in enhanced sampling methods.
• The technique accurately recovers free-energy landscapes and reveals complex molecular interactions, particularly in metal-organic frameworks.