Phase Behavior of Materials with Isotropic Interactions Designed by Inverse Strategies to Favor Diamond and Simple Cubic Lattice Ground States

TL;DR

This study uses molecular simulations to map phase diagrams of two isotropic interaction models designed to favor diamond and simple cubic structures, revealing complex polymorphic behavior and multiple phase transitions.

Contribution

It demonstrates how inverse design of isotropic interactions can produce materials with targeted lattice ground states and rich phase behavior.

Findings

Both models exhibit stable diamond and simple cubic phases.

Presence of multiple crystalline phases including hexagonal and BCC.

Observation of reentrant melting transitions.

Abstract

We use molecular simulation to construct equilibrium phase diagrams for two recently introduced model materials with isotropic, soft-repulsive pair interactions designed to favor diamond and simple cubic lattice ground states, respectively, over a wide range of densities [Jain et al., Soft Matter 9 14 (2013)]. We employ free energy based Monte Carlo simulation techniques to precisely trace the inter-crystal and fluid-crystal coexistence curves. We find that both model materials display rich polymorphic phase behavior featuring stable crystals corresponding to the target ground-state structures, as well as a variety of other crystalline (e.g., hexagonal and body-centered cubic) phases and multiple reentrant melting transitions.