Percolation transition and bimodal density distribution in hydrogen fluoride

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Physics

Background:

• Hydrogen-bond networks are crucial for the properties of associating fluids like water.
• Strong hydrogen bonding in molecules such as hydrogen fluoride (HF) can lead to unique network structures.
• Understanding these networks is key to characterizing liquid phase behavior.

Purpose of the Study:

• To investigate the hydrogen bond network topology of liquid hydrogen fluoride (HF) using molecular dynamics simulations.
• To identify and characterize phase transitions within the HF liquid phase.
• To explore the cohesive mechanisms and structural heterogeneity in liquid HF.

Main Methods:

• Conducting molecular dynamics simulations of hydrogen fluoride (HF).
• Analyzing the hydrogen bond network connectivity and topology.
• Identifying percolation transitions and structural differences in the liquid phase.

Main Results:

• Evidence of a second-order percolation transition in the HF hydrogen bond network below the critical point.
• Identification of two distinct cohesive mechanisms: polymer-like chains at low temperatures and dispersion-bound oligomers at higher temperatures.
• Observation of significant structural heterogeneity, with two distinct liquid populations exhibiting different local densities.

Conclusions:

• Liquid HF displays a unique second-order percolation transition, unlike most small molecular liquids.
• The transition highlights two different mechanisms of liquid cohesion in HF.
• The study reveals marked structural heterogeneity in liquid HF, with implications for its physical properties.