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

• Published in: Materials Vol. 10; no. 11; p. 1280
• Main Authors: Gabriëlse, Alexander, Löwen, Hartmut, Smallenburg, Frank
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 07.11.2017; MDPI
• Subjects: Computer simulation; Crystal lattices; Crystal structure; Low temperature; Phase diagrams; cell theory; hard core square-shoulder model; computer simulation; phase behavior; colloidal crystals
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma10111280

In many cases, the stability of complex structures in colloidal systems is enhanced by a competition between different length scales. Inspired by recent experiments on nanoparticles coated with polymers, we use Monte Carlo simulations to explore the types of crystal structures that can form in a simple hard-core square shoulder model that explicitly incorporates two favored distances between the particles. To this end, we combine Monte Carlo-based crystal structure finding algorithms with free energies obtained using a mean-field cell theory approach, and draw phase diagrams for two different values of the square shoulder width as a function of the density and temperature. Moreover, we map out the zero-temperature phase diagram for a broad range of shoulder widths. Our results show the stability of a rich variety of crystal phases, such as body-centered orthogonal (BCO) lattices not previously considered for the square shoulder model.