Structure and property exploration of two-dimensional, bulk, and cluster lithium sulfide using the IM2ODE method†

Abstract

Lithium sulfide (Li₂S) plays an important role in fields such as energy, environment and semiconductors. Exploration of the microstructure of Li₂S has significant implications for developing new materials and optimizing related material properties. In this work, the inverse design of materials by the multi-objective differential evolution (IM²ODE) method combined with density functional theory (DFT) calculations was used to predict the two-dimensional (2D), three-dimensional (3D), and cluster structures of Li₂S. Their structural stabilities and electronic properties were further investigated. Novel monolayer and double-layer hexagonal structures of 2D Li₂S are predicted. The double-layer structure has better thermal stability and a wider band gap of 3.5 eV than the single-layer structure. Various novel structures of 3D Li₂S are predicted. Some structures are similar to 1T-MoS₂ and the double-layer hexagonal structure of 2D Li₂S. With increasing number of atoms, the (Li₂S)_n clusters converge into a cage-like structure and their average binding energies decrease. The second-order energy differences of (Li₂S)_n clusters show an odd–even oscillation rule. The ionization potentials, electron affinities, electronegativities, and chemical hardnesses also decrease. These findings should improve theoretical understanding of the properties and behavior of new 2D, 3D, and cluster functional materials.