Low-Temperature Crystal Structures of the Hard Core Square Shoulder Model

Area of Science:

• Colloidal science
• Materials science
• Computational physics

Background:

• Colloidal system stability is often governed by interactions across multiple length scales.
• Recent experiments show polymer-coated nanoparticles forming complex structures.
• Understanding these structures requires models that capture competing interactions.

Purpose of the Study:

• To investigate crystal structure formation in a hard-core square shoulder model with two favored distances.
• To explore the influence of competing length scales on colloidal self-assembly.
• To identify novel crystal phases in this model system.

Main Methods:

• Utilizing Monte Carlo simulations for structure searching.
• Employing mean-field cell theory to calculate free energies.
• Constructing phase diagrams as a function of density, temperature, and square shoulder width.

Main Results:

• Discovery of a rich variety of stable crystal phases.
• Identification of body-centered orthogonal (BCO) lattices, previously unconsidered for this model.
• Detailed phase diagrams illustrating structural transitions under varying conditions.

Conclusions:

• The hard-core square shoulder model effectively predicts complex colloidal structures.
• Competing length scales drive the formation of diverse and novel crystal phases.
• This work expands the known phase behavior for systems with multiple interaction potentials.