Crystal structures and freezing of dipolar fluids.

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Materials Science

Background:

• Understanding the ground state crystal structures of systems with dipole-dipole interactions is crucial for materials science.
• Classical systems of spherical particles with embedded point dipoles exhibit complex phase behavior.
• Previous studies have explored various interactions, but a comprehensive analysis of dipolar soft spheres is needed.

Purpose of the Study:

• To investigate the ferroelectric ground state crystal structures of classical systems of spherical particles with embedded point dipoles at T=0.
• To calculate the ground state energy using generalized Ewald summation techniques.
• To map the phase diagrams for both Stockmayer and dipolar soft sphere potentials.

Main Methods:

• Utilized generalizations of the Ewald summation technique for accurate ground state energy calculations.
• Analyzed the crystal structures, noting reduced symmetry compared to nonpolar systems.
• Employed density-functional theory to study the freezing of the Stockmayer fluid.

Main Results:

• Identified three distinct ferroelectric phases (hexagonal, body-centered orthorhombic, body-centered tetragonal) for the Stockmayer potential with increasing dipole moment.
• Discovered a richer phase diagram for dipolar soft spheres with repulsive inverse power law potentials.
• Observed a crossover in phase sequences near the exponent n=12 for dipolar soft spheres.
• Determined that crystals with dipoles are never strictly cubic due to reduced symmetry.

Conclusions:

• The study elucidates the complex phase behavior of dipolar systems, crucial for understanding ferroelectric materials.
• The identified phases and phase diagram provide valuable insights for designing electro- and magnetorheological fluids.
• The findings contribute to the fundamental understanding of phase transitions in soft matter systems.