Liquid and glass polymorphism in a monatomic system with isotropic, smooth pair interactions

Area of Science:

• Statistical Mechanics
• Computational Physics
• Materials Science

Background:

• The Jagla potential models water-like anomalies and liquid-liquid phase transitions but has discontinuous forces unsuitable for standard molecular dynamics (MD) simulations.
• Existing potentials often struggle to accurately represent the complex behavior of tetrahedral liquids, including water.

Purpose of the Study:

• To introduce a smooth, computationally tractable version of the Jagla potential, termed the 'Fermi-Jagla' potential.
• To investigate the thermodynamic anomalies and phase behavior of liquids described by the Fermi-Jagla potential using MD simulations.
• To assess the suitability of the Fermi-Jagla potential for modeling tetrahedral liquids and glass phenomenology.

Main Methods:

• Development of a smooth Fermi-Jagla pair potential based on two Fermi distributions.
• Standard molecular dynamics (MD) simulations to study systems interacting via the Fermi-Jagla potential.
• Analysis of thermodynamic properties, including density, compressibility, specific heat, and diffusivity.
• Investigation of liquid-liquid phase transitions (LLPT) and polyamorphism in the glass state.

Main Results:

• The Fermi-Jagla potential successfully reproduces water-like anomalies: decreasing density, increasing compressibility and specific heat upon cooling, and increasing diffusivity upon compression.
• A liquid-liquid phase transition (LLPT) with a negative slope in the P-T plane was observed, making it a better model for tetrahedral liquids than the original Jagla potential.
• Reversible polyamorphism between low- and high-density amorphous solids (LDA and HDA) was found, with HDA arising from pressure-induced amorphization.
• The potential's smoothness allows for easy implementation in MD simulations and facilitates the study of glass phenomenology by avoiding spontaneous crystallization.

Conclusions:

• The Fermi-Jagla potential is a viable and computationally efficient alternative to the original Jagla potential for simulating water-like anomalies and LLPT.
• Its negative-sloped LLPT line and ability to model polyamorphism make it a promising candidate for studying tetrahedral liquids and glasses.
• The smooth nature of the Fermi-Jagla potential enhances its applicability in standard MD simulations for exploring complex liquid and glass behaviors.