Size-temperature phase diagram for small Lennard-Jones clusters

Area of Science:

• Computational physics and physical chemistry.
• Thermodynamics and statistical mechanics of small systems.

Background:

• Understanding phase transitions in finite systems like clusters is crucial for bridging the gap between bulk matter and individual molecules.
• Lennard-Jones clusters provide a fundamental model system for studying interatomic interactions and emergent collective behaviors.

Purpose of the Study:

• To construct a detailed size-temperature phase diagram for small Lennard-Jones clusters (LJn, n ≤ 147).
• To identify and characterize different types of phase transitions occurring in these finite systems.
• To investigate the influence of surface structure, specifically Mackay packing, on phase behavior.

Main Methods:

• Utilizing the parallel tempering Monte Carlo method to compute heat capacities (Cv(T)).
• Analyzing computed heat capacities to identify thermodynamic signatures of phase transitions.
• Constructing the phase diagram based on the temperature-dependent heat capacity data.

Main Results:

• A comprehensive size-temperature phase diagram for LJn clusters (n ≤ 147) was successfully generated.
• Two distinct phase transitions were identified: a higher-temperature solid-liquid transition associated with core melting, and a lower-temperature transition related to surface layer melting.
• The surface layer melting transition was found to be contingent upon the presence of Mackay packing in the overlayer.

Conclusions:

• The study elucidates the complex phase behavior of small Lennard-Jones clusters, revealing distinct melting mechanisms.
• The findings highlight the critical role of surface structure and packing in influencing the thermodynamic properties and phase transitions of finite systems.
• This work provides valuable insights into the fundamental physics governing phase transitions in nanoscale matter.