Structure Prediction And Related Properties Study Of New Functional Materials

The problem of materials is one of the important factors which restrict the development of technologies.Accelerating the speed of development of new functional materials are significant.The conventional way of discovering new materials is a process of trial-and-error in experiment,which to a great extent lies on the chemical intuition and accumulated experience.However it needs a painstakingly long and costly process.With the development of first-principle study and improvement of computer performance,simulation of materials based on first-principle quantum mechanics calculation has become a powerful tool for materials discovery.The simulation do not have a process of trial-and-error,which is more efficient and cheap.Therefore,structure prediction based on first principle study has received broad attentions.Physical environment and dimensional changing of the materials will lead to special properties.Such as,superconductive and superhard materials discovery at high pressure and two-dimensional materials which is rising in the recent decade.However,it is too hard to get ultra-high pressure environment and synthesize two-dimensional materials.Simulation based on first principle study can get the stability,electronic properties and mechanical properties at a short time,which will guide for experiment and reduce the process of trial-and-error.Therefore,research on special environment and low dimension has import science significance for developing of new materials.In this background,we conducted detailed studies of the structure prediction and related properties of several new functional materials.The structure of the present paper is organized as follows:Chapter one introduces the significance and research status of structure prediction.Chapter two introduces the theoretical basis of first principle study and structure prediction.Chapter three shows new structures of ScH_n at high pressure and their superconductivities.Chapter four introduce two-dimensional Be₂C with octacoordinated carbon and negative Poisson's ratio.Chapter five shows a theoretical study of MX₂ with high carrier mobility.Chapter six is the conclusion and the possible future work.Based on theoretical calculation,we got the following conclusions:1.We prediction three other metallic stoichiometries of ScH₄,ScH₆,and ScH₈,which show superconductivity at significantly higher temperatures.The stability of ScH₄ and ScH₆ does not require extremely high pressures?<150 GPa?.The present electron-phonon calculations revealed the superconductive potential of ScH₄ and ScH₆ with estimated Tc of 98 K and129 K at 200 GPa and 130 GPa,respectively.2.We predicted three new two-dimensional?2D?Be₂C structures,namely,?-Be₂C,?-Be₂C,and?-Be₂C,on the basis of density functional theory computations and the particle-swarm optimization method.In?-Be₂C,a carbon atom binds to eight Be atoms,forming an octacoordinate carbon moiety.This is the first example of an octacoordinate carbon containing material.The other two structures,?-Be₂C and?-Be₂C,are quasi planar hexacoordinate carbon containing 2D materials.More interestingly,these predicted new phases of Be₂C all have unusual negative Poisson's ratios.3.Two-dimensional binary MX₂?M=Ni,Pd and Pt,X=P and As?exhibiting a beautiful pentagonal ring network is discussed through first principle calculations.We predict that MX₂ sheets possess narrow direct band gaps of about 0.3⁰.8 eV and ultra high carrier mobilities both for hole and electron(>1×10⁴cm²V^-1s^-1).The hole mobility of PdAs₂ is even up to 50×10⁴cm²V^-1s^-1 and the electron mobility of PtAs₂ is up to25×10⁴cm²V^-1s^-1.