Prediction of new functional materials via evolutionary algorithm and ab initio study of their potential applications

Abstract

Discovering new functional materials often drives significant innovation for industrial applications and provides new insights into fundamental scientific issues. New phases of materials or new materials often possess unprecedented properties. Therefore, crystal structure prediction (CSP) and investigation of its potential applications have attracted extensive research attention. New materials could be obtained by altering external environmental parameters such as pressure and epitaxial strain, and by tailoring intrinsic material parameters, such as dimensionality (for instance, moving from 3D bulk to 2D layered samples). In this dissertation, efforts have been focused in the following three areas: First, the ground-state structures of superconducting Nb3Al under high pressures and the unprecedented stoichiometries of Na-Pt compounds under high pressures were predicted using the ab initio evolutionary algorithm. New crystal structures of Nb3Al at various pressures and low temperatures were uncovered. The Allen-Dynes modified McMillan equation was utilized to calculate the superconducting transition temperature of Nb3Al, and the result is in good agreement with experimental results. Using first-principles calculations combined with the evolution algorithm, several Na-rich platinides were discovered in the Na-Pt system. Among them, the predicted Na2Pt and a low-pressure phase of Na4Pt were synthesized experimentally. Second, the evolutionary algorithm was further used to predict two-dimensional (2D) allotropes of group VA elements (P, As, Sb, and Bi), and several competing 2D allotropes of arsenic were selected as representatives for intensive investigation. In addition to previously reported 2D allotropes in group VA elements, several new 2D crystal polymorphs of group VA elements were uncovered. Bandgaps of 2D semiconducting allotropes could cover a wide energy range, which would facilitate broadband applications. In addition, several metallic 2D motifs were newly proposed. Additionally, band engineering, possible hybridization, and transition routes between different arsenene allotropes were investigated in detail. This provides more possibilities for new applications. Third, theoretical evaluations of black arsenene (B-As) with DFT methods combined with non-equilibrium Green’s function (NEGF) formalism have been conducted to explore transport properties and potential sensor applications. Our results showed that B-As is sensitive to nitrogen-containing gases and SO2 and could be further modulated by a vertical electric field due to charge transfer between the gas molecules and B-As. In addition, the transport features show large anisotropy directed along different directions (armchair and zigzag). Spin-polarized currents could be obtained after the adsorption of NO and NO2. Furthermore, a more isotropic electrical conductance of B-As could be obtained by the application of biaxial strain, which can also effectively enhance the response toward SO2.