State variables for glasses: The case of amorphous ice

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Materials Science

Background:

• Glasses are complex out-of-equilibrium systems not fully described by traditional thermodynamic variables.
• The potential energy landscape (PEL) formalism offers a framework for understanding supercooled liquids and glasses.
• Amorphous ices (LDA and HDA) provide a model system for studying glassy states due to their distinct phase transitions.

Purpose of the Study:

• To identify a comprehensive set of state variables that uniquely define the condition of a glass.
• To investigate the applicability of the PEL formalism in characterizing amorphous ice transformations.
• To determine if these state variables can be generalized to other amorphous solids.

Main Methods:

• Utilized computer simulations with the ST2 water model to study amorphous ice transformations.
• Prepared distinct low-density amorphous ice (LDA) and high-density amorphous ice (HDA) samples with varied preparation histories.
• Analyzed sample evolution under compression, decompression, and heating at low temperatures, avoiding annealing.

Main Results:

• The evolution of amorphous ice samples under external stimuli (compression, heating) is uniquely determined by six macroscopic properties.
• These six properties include three conventional thermodynamic variables (N, V, T) and three PEL-derived properties (E_IS, P_IS, S_IS).
• The set (N, V, T, E_IS, P_IS, S_IS) effectively defines the glass state for amorphous ice.

Conclusions:

• The six identified variables (N, V, T, E_IS, P_IS, S_IS) serve as a complete set of state variables for amorphous ice.
• These findings support the utility of the PEL formalism in defining glassy states.
• The identified state variables may be applicable to amorphous solids more broadly, with potential for fewer variables in specific cases.