Weak links between fast mobility and local structure in molecular and atomic liquids

Area of Science:

• Condensed matter physics
• Computational chemistry
• Materials science

Background:

• Supercooled liquids exhibit complex dynamics, including fast particle mobility.
• Understanding the relationship between local structure and dynamics is crucial for liquid state theory.

Purpose of the Study:

• To investigate the relationship between fast particle mobility and cage geometry in supercooled molecular and atomic liquids.
• To explore the influence of cage size, shape, and local forces on particle rattling dynamics.

Main Methods:

• Molecular-dynamics simulations of dense molecular (linear trimers) and atomic (binary mixtures) liquids.
• Utilized Lennard-Jones and Mie potentials to model interparticle interactions.
• Analyzed correlations between fast mobility, cage geometry, and local forces on a per-particle and subset basis.

Main Results:

• Weak correlations found between fast mobility and cage geometry on a per-particle basis.
• Grouping particles and cages revealed increased fast mobility with larger and more aspherical cages.
• Local forces within the first neighbor shell did not correlate with fast mobility in molecular liquids.

Conclusions:

• Cage geometry alone cannot fully explain the link between fast mobility and structural relaxation.
• Particle fast dynamics are likely influenced by collective effects extending beyond the immediate neighbors.
• Extended fast modes may play a significant role in the dynamics of supercooled liquids.