Relative pair dynamics in simple supercooled liquids: longitudinal contributions.

Area of Science:

• Condensed matter physics
• Materials science
• Computational chemistry

Background:

• Understanding atomic and molecular dynamics is crucial for characterizing material properties.
• Pair correlation functions provide insights into interatomic interactions and system behavior.

Purpose of the Study:

• To investigate the pair dynamics of simulated argon across different thermodynamic states (crystal, melting, supercooled, quenched liquid).
• To analyze the longitudinal dynamics and its temperature dependence.
• To relate pair dynamics to the density of states (DOS) and diffusivity.

Main Methods:

• Simulating argon samples at various temperatures (20 K, 55 K, 85 K).
• Tracking tagged pairs and evaluating specific correlation functions, deltaB(r(0);t).
• Analyzing the power spectrum of deltaB(r(0);t) to obtain the density of states (DOS).
• Modeling relaxation processes using damped harmonic oscillator (DHO) functions and exponential functions.

Main Results:

• Oscillatory behavior in deltaB(r(0);t) observed, varying with temperature and initial pair distance.
• Crystal dynamics show rapid decay of oscillations, while supercooled liquids exhibit a temperature-dependent plateau.
• Power spectrum of deltaB(r(0);t) correlates with DOS, revealing Einstein and Debye frequencies in crystals.
• Liquid states show memory of crystal vibrational modes, with an additional low-frequency contribution impacting DOS and diffusivity.

Conclusions:

• Pair dynamics are sensitive to the thermodynamic state of argon.
• Liquid states exhibit complex dynamics, retaining vibrational memory from the solid phase.
• A low-frequency DOS excess in liquids influences diffusivity, especially near the glass transition temperature.