A structural approach to vibrational properties ranging from crystals to disordered systems

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Physics

Background:

• Vibrational anomalies in disordered solids are often attributed to structural disorder, but this remains a subject of debate.
• Understanding these anomalies is crucial for characterizing amorphous materials.

Purpose of the Study:

• To investigate the relationship between structural disorder and vibrational properties in two-dimensional packings.
• To explore the role of local structural features, termed 'softness,' in anomalous vibrational behavior.

Main Methods:

• Simulations of two-dimensional packings tuned from crystalline to amorphous states, and varying densities.
• Analysis of vibrational density of states and reduced density of states to observe the boson peak.
• Application of a novel machine-learning method to identify and quantify local structural 'softness' and its heterogeneity.

Main Results:

• The boson peak's evolution was clearly observed with changes in disorder and volume fractions.
• A strong monotonic relationship was found between the boson peak's shape and the system's softness and its spatial heterogeneity.
• Soft regimes were identified as key structural features influencing vibrational anomalies.

Conclusions:

• The study suggests that local structural 'softness' is a significant factor in the anomalous vibrational properties of amorphous solids.
• Softness and its spatial distribution offer a potential new structural perspective for understanding boson peak anomalies.
• This work provides insights into the fundamental physics of disordered materials.