The Electronic Structures, Crystal Structures And Properties Of Metallic Compounds By Computer Simulation

Over the past eighty decades, twenty thousand metallic compounds have been found, and about three hundred metallic compounds may be used in our live. Their have abundant type structures and properties. When tiny metallic compounds presence in metallic alloys with grain type, the total strength of the alloys will be enhanced. Especially, when the temperature heightens in a certain range the strength of metallic alloys will be also enhanced, which is the potential advantage of they applying for structural materials at high temperature. The most application of the "high temperature hero" is in aviation and spaceflight, for example; titanium aluminium compounds with small density, high melting and high temperature properties have favorable applied foreground. Besides for high temperature materials, the others properties of metallic compounds have also been found one by one. Usually, metallic compounds have good mechanical, high melting point, oxidation and corrosiveness resistance properties, so they can be used for important structural materials in aviation, spaceflight, traffic and machine industries; owing to the acoustical, optical, electrical and magnetic physical properties, metallic compounds can be used for semiconductor, magnetism, hydrogen storage and superconductive materials and have abundant application foreground. At the same time, the broad applications of metallic compounds promote up-to-date technique, also make the instrument abbreviated, lightweight, compositive and intellective, and cause the new instrument.Metallic compounds with particular properties and broad application are the investigative hotspot now. Along with the quickly developing society, our living qualities enhance, and the requirements of us are more and more, thus, many metallic compounds with particular properties are needed by us. However, we can directly observe the materials only in atomic level, for example:using TEM to observe the atomic distribution or using X-ray to analyze the crystal structure of the materials, these techniques is lacking and make against us to understand the essence of the materials. In order to develop new materials and new properties more and more quickly, judging the element in electronic level and analyzing the electronic state are very importance. Along with the development of computer technology, the calulational ability is enhancing. These is more favorable for researching the properties of metallic compounds in atomic level by the first theory calculation which can investigate the atomic and electric structures more profound. Based on the above consideration, in this article, the mechanical, optical and structural properties have been calculated by first principle calculations based on density functional theory. The main results obtained are list in following:Firstly, we investigate the dielectric constant of binary metallic compounds that are semiconductors. We have indicated that the s electrons levels of non-metals with much lower transition probability than other valence, which results in the mistake estimate for Levine model. By first principle calculations, we have found that the s electron levels of non-metals can only contribute a half of the levels on the total valence. Thus, Levine model should be improved, which leads to more accurate prediction on dielectric constants and average optical energy gap of transition metallic compounds.Secondly, we investigate the chemical bonds of binary metallic compounds that are conductors. Owing to the partly metallic bonding in it, Phillips model cannot analyze them chemical bonds. By first principle calculations, we have found that the percentage of metallic bonding in multiplex chemical bonds is large for the most compounds and cannot be ignored. The redefinition of Phillips ionicity results in well correspondence for the bulk modulus and hardness calculation of TM carbides and nitrides. It is confirmed that the s-p-d hybridization in TM carbides and nitrides indeed enhances the hardness of materials.Thirdly, the band structures, PDOS and electronic configuration of CaPtSe half-Heusler compounds have been simulated using LDA+U. The results show that both the covalent Pt-Se bonds and the ionic Pt-Ca bands contribute the band structures where there is the smallest value of (EΓ6-EΓ8) or the strongest spin-orbit coupling. When more HHCs are compared, it is found that the smaller positive△ZY and△YX are, the better topological insulator is. When-0.28<△ZY<0, a more negative△ZY value gives a lower (EΓ6-EΓ8) value. Moreover, X and Z lying in II and VI groups are propitious to form topological insulators.Fourthly, the band structures, PDOS and electronic configuration of several AB2C full-Heusler compounds have been simulated using LDA+U. The results show that full-Heusler compounds with half-filled d orbitals and d5d5s2p6 electronic structures can also form TIs, which will double enlarge the range of topological insulators candidates. The band structures of full-Heusler compounds are affected by the covalent bonding of A-B and B-C jointly. The spin-up and spin-down electrons influence the orbitals respectively, which induce the magnetism of the materials. All FHCs with the magnetic moments about 9μB are antiferromagnets, which can lead to the image magnetic monopole effect and provide a new design of a tunable optical modulator. Fifthly, FeCrCoNiCu alloy and FeMoCrNiCu alloy consist of a single FCC solid solution. When Cu or Co in the alloys is substituted by Al, the microstructures of the alloys change to that of a single BCC solid solution or that of a BCC+FCC solid solution. Cu with a FCC structure promotes the formation of a FCC solid solution, while A1 with a FCC structure does not help the formation of a FCC solid solution and promotes the formation of a FCC solid solution. In addition, when Zr is added into the alloys, complicated compounds are present due to the stronger chemical combination tendency between Zr and other components. The hardness of alloys with a BCC structure possesses is higher than that of the alloys with a FCC structure. When complicated compounds form, the hardness increases further due to the strengthening of the second phase precipitation.Finally, the structures of a series of fabricated high entropy alloys are examined experimentally and theoretically. Since the electronegativities of the principle components in the high entropy alloys are different and the principle components in the v alloys could be divided into two groups. Large compound formation tendency of the high entropy alloys is found where Al and Cr have been used as the principal components. As result, the solidified solid solution has a B2 structure, not an A2. This is confirmed by the computer simulation.Although this is only part metallic compounds and part properties have been researched, we can investigate more by first principle calculations. By combining the chemical bonds of the materials with them properties closely, we will excavate more materials with new properties.