Prediction Of Several New Materials

We design several new structure materials and predict their properties based on first principles calculations.These include two-dimensional gold in honeycomb structure and a series new materials in diamond-like structure which is constructed by X atom centered XN₄ tetrahedra and N-N dimer fundamental units.The main results are as below.Firstly,we prove that two-dimensional honeycomb gold is relatively stable owing to its strong relativistic effect and electronic configuration by first principles calculations.It has covalent bond and semiconductor band structure with a gap of 0.1eV.Tailoring it into nanoribbons with the armchair type of edges,its band gap can be further widen to about 0.3 eV.In contrast,single layer of close packed plane gold is metallic.Both of them are more transparent to visible light compared with graphene.They are potential candidates in transparent conductive materials and electronic logic devices.In experiments,we try to get two-dimensional honeycomb gold by dealloying BaAu₂.The deposit is nanoporous gold.Some honeycomb atomic patterns are observed in suspension.It needs further demonstration.Secondly,we construct a diamond-like structure by using Si centered SiN₄tetrahedra and N=N dimers as the fundamental building units.The high density of delocalized electrons provided by?*antibond in N=N is crucial for its high electronic conductivity.It's stable in lattice dynamics and relatively energy favored.A striking feature is that it has free-electron energy dispersions in its band structure.It will serve as a good low-density?0.996 g/cm3?metal candidate with a high electrical conductivity?5.07×10⁵ S/cm?,a high thermal conductivity?371 W/m?K?comparable to copper,and ordered cavities?7.4??.AlN₄ in isostructure is also stable and has similar band structure.The results presented here show that nitrogen dimers can be used as proper fundamental building units to design new compounds with high conductivity.Lastly,we replaces Si in SiN₄ by M,where M is 3d transition metal elements.By comparing their ferromagnetic and antiferromagnetic energy,and calculating corresponding band structure,we find that FeN₄,CoN₄ and MnN₄ are half metals with band gaps larger than 2 eV in one spin direction.They are stable in thermal dynamics and lattice dynamics.N-N bond acts as a bridge for conducting carriers and helps neighboring 3d transition metal atoms realize ferromagnetic coupling.The hybridization between N's and M's atomic orbitals lead to the formation of bonding and antibonding states in one spin direction and opening a band gap.Their curie temperatures are much higher than room temperature,which enables them to become candidates for practical spintronics application.