Phase behavior of the quantum Lennard-Jones solid.

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Materials Science

Background:

• The Lennard-Jones (LJ) potential models interactions in noble gas solids.
• Classical LJ solids show hexagonal close-packed (hcp) and face-centered cubic (fcc) phase transitions.
• The quantum LJ solid phase behavior is largely unexplored.

Purpose of the Study:

• Investigate the phase stability of quantum LJ solids.
• Determine the influence of quantum effects on hcp and fcc phases.
• Explore implications for noble gas solid phase behavior.

Main Methods:

• Thermodynamic integration using path integral molecular dynamics (PIMD).
• Lattice dynamics calculations.
• Analysis of quantum effects on crystal structure stability.

Main Results:

• Quantum effects stabilize the hcp phase in PIMD simulations.
• Lattice dynamics favor the fcc phase.
• A re-entrant low-pressure fcc phase is suggested for highly quantum systems.
• For helium parameters, quantum melting occurs, destabilizing both structures at zero pressure.

Conclusions:

• Quantum effects significantly alter the phase diagram of LJ solids.
• The interplay between quantum effects and crystal structure is crucial for understanding noble gas solids.
• Zero-point vibrations lead to quantum melting in systems like helium.