Phase changes in Lennard-Jones mixed clusters with composition Ar(n)Xe(6-n) (n=0,1,2)

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding phase transitions in small clusters is crucial for molecular science.
• Lennard-Jones clusters provide a fundamental model for studying interatomic interactions and phase behavior.

Purpose of the Study:

• To investigate the phase behavior of binary six-atom mixed Lennard-Jones clusters, Ar(n)Xe(6-n) (n=0,1,2).
• To identify and characterize phase transitions using heat capacity and dynamical properties.

Main Methods:

• Parallel tempering Monte Carlo simulations to calculate configurational heat capacity (C(V)(T)).
• Molecular dynamics simulations to investigate dynamical properties like interbasin isomerization rate and bond fluctuation parameter.
• Monte Carlo quenching for structural analysis.

Main Results:

• All studied Ar(n)Xe(6-n) clusters exhibited a heat capacity feature between 15-20 K, assigned to a solid-liquid phase change.
• The Ar(2)Xe(4) cluster showed an additional heat capacity peak near 7 K, attributed to a solid-solid phase change.
• Dynamical properties at 7 K (low isomerization rate, low bond fluctuation) contrasted with those at 20 K (high isomerization rate, higher bond fluctuation).

Conclusions:

• The 15-20 K heat capacity feature corresponds to a solid-liquid phase transition.
• The 7 K peak in Ar(2)Xe(4) signifies a solid-solid phase transition.
• This work presents evidence for solid-solid phase change behavior in the smallest Lennard-Jones cluster system to date.