Lattice Defects

Two-dimensional (2D) lattice materials with well-designed microstructures exhibit extraordinary properties such as zero and negative Poisson’s effects, and play a crucial role in industrial fields. However, inevitable defects from manufacturing, storage, transportation, and service may compromise their microstructures and functionalities. Therefore, it is important but still unclear: which microstructures and associated properties are most or least sensitive to defects.

In this paper we extend the classical method of lattice dynamics to defective crystals with partial symmetries. We start by a nominal defect configuration and first relax it statically. Having the static equilibrium configuration, we use a quasiharmonic lattice dynamics approach to approximate the free energy. Finally, the defect structure at a finite temperature is obtained by minimizing the approximate Helmholtz free energy. For higher temperatures we take the relaxed configuration at a lower temperature as the reference configuration.