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Hexatic phase and cluster crystals of two-dimensional GEM4 spheres
Santi Prestipino1, Franz Saija2
1Dipartimento di Fisica e di Scienze della Terra, Università degli Studi di Messina, Contrada Papardo, I-98166 Messina, Italy.
The Journal of Chemical Physics
|November 17, 2014
Summary
The two-dimensional generalized exponential model 4 (GEM4) system exhibits unique melting behavior. It forms multiple crystal phases, with only the ordinary crystal melting into a hexatic phase before reaching a disordered cluster state.
Area of Science:
- Condensed matter physics
- Materials science
- Statistical mechanics
Background:
- Two-dimensional crystals exhibit unique melting behavior, including a two-step process via a hexatic phase.
- Three-dimensional systems with soft potentials can form cluster crystals with multiple particles per lattice site.
Purpose of the Study:
- Investigate the phase behavior of the two-dimensional generalized exponential model 4 (2D GEM4) system.
- Explore the combined effects of low dimensionality and potential softness on crystal formation and melting.
Main Methods:
- Density-functional theory calculations.
- Numerical free-energy calculations.
Main Results:
- The 2D GEM4 system forms one ordinary and several cluster triangular-crystal phases.
- Only the ordinary crystal melts into a hexatic phase.
- Cluster crystals merge into a single phase with pressure-modulated site occupancy upon heating.
Conclusions:
- The 2D GEM4 system displays complex phase behavior, including distinct ordinary and cluster crystal structures.
- Melting pathways are dependent on crystal type, with only the ordinary crystal exhibiting hexatic intermediate.
- A unified cluster phase emerges at higher temperatures, characterized by variable site occupancy.
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