运用量子化学计算预测铽离子配体三重态能级的方法研究

以邻氨基苯甲酸(HL)为第一配体,邻菲啰啉(Phen)、三苯基氧膦(TPPO)为中性配体合成了3种铽配合物,测定了配合物的红外光谱,结果表明,邻氨基苯甲酸的氨基和羧基均与稀土离子发生配位,邻菲啰啉和三苯基氧膦也均与稀土离子配位;通过紫外光谱和荧光光谱对比研究了其发光性能,发光强度顺序为Tb(L)3(TPPO)2>Tb(L)3(H2O)2>Tb(L)3(Phen),通过量子化学计算出配体的最高已占分子轨道(HOMO)、最低未占分子轨道(LUMO)能级及单重态和三重态能级,对比分析了不同中性配体铽配合物的能量传递过程。

Electronic band transformation from indirect gap to direct gap in Si-H compound

The electronic band structures of periodic models for S^H compounds are investigated by the density functional theory. Our results show that the Si H compound changes from indirect-gap semiconductor to direct-gap semiconductor with the increase of H content. The density of states, the partial density of states and the atomic charge population are examined in detail to explore the origin of this phenomenon. It is found that the Si-Si bonds are affected by H atoms, which results in the electronic band transformation from indirect gap to direct gap. This is confirmed by the nearest neighbour semi-empirical tight-binding （TB） theory.

An easy and efficient way to treat Green's function for nano-devices with arbitrary shapes and multi-terminal configurations

The efficiency of the calculation of Green＇s function （GF） for nano-devices is very important because the calculation is often needed to be repeated countlessly. We present a set of efficient algorithms for the numerical calculation of GF for devices with arbitrary shapes and multi-terminal configurations. These algorithms can be used to calculate the specified blocks related to the transmission, the diagonals needed by the local density of states calculation, and the full matrix of GF, to meet different calculation levels. In addition, the algorithms for the non-equilibrium occupation and current flow are also given. All these algorithms are described using the basic theory of GF, based on a new partition strategy of the computational area. We apply these algorithms to the tight-binding graphene lattice to manifest their stability and efficiency. We also discuss the physics of the calculation results.

Strain Effects in Graphene and Graphene Nanoribbons:The Underlying Mechanism

A tight-binding analytic framework is combined with first-principles calculations to reveal the mechanism underlying the strain effects on electronic structures of graphene and graphene nanoribbons(GNRs).It provides a unified and precise formulation of the strain effects under various circumstances-including the shift of the Fermi(Dirac)points,the change in band gap of armchair GNRs with uniaxial strain in a zigzag pattern and its insensitivity to shear strain,and the variation of the k-range of edge states in zigzag GNRs under uniaxial and shear strains which determine the gap behavior via the spin polarization interaction.

Strong interlayer coupling in phosphorene/graphene van der Waals heterostructure： A first-principles investigation

Based on first-principles calculations within the framework of density functional theory, we study the electronic properties of phosphorene/graphene heterostructures. Band gaps with different sizes are observed in the heterostructure, and charges transfer from graphene to phosphorene, causing the Fermi level of the heterostructure to shift downward with respect to the Dirac point of graphene. Significantly, strong coupling between two layers is discovered in the band spectrum even though it has a van der Waals heterostructure. A tight-binding Hamiltonian model is used to reveal that the resonance of the Bloch states between the phosphorene and graphene layers in certain K points combines with the symmetry matching between band states, which explains the reason for the strong coupling in such heterostructures. This work may enhance the understanding of interlayer interaction and composition mechanisms in van der Waals heterostructures consisting of two-dimensional layered nanomaterials, and may indicate potential reference information for nanoelectronic and optoelectronic applications.

The roles of electrons in the electronic structures and optical properties of graphyne

The electronic structures and optical properties of graphyne consisting of sp-and sp 2-hybridized carbon atoms are studied using first-principles calculations.A tight-binding model of the 2p z orbitals are proposed to describe the electronic bands near the Fermi level.The results show that the natural band gap of graphyne originates from the inhomogeneous bindings between differently-hybridized carbon atoms.The interlayer interactions of bulk graphyne narrow the band gap to 0.16 eV and result in redshift of the optical spectral peaks as compared to single-layered graphyne.

Molecular heterostructure by fusing graphene nanoribbons of different lengths through a pentagon ring junction

Graphene nanoribbons(GNRs)have attracted great research interest because of their widely tunable and unique electronic properties.The required atomic precision of GNRs can be realized via on-surface synthesis method.In this work,through a surface assisted reaction we have longitudinally fused the pyrene-based graphene nanoribbons(pGNR)of different lengths by a pentagon ring junction,and built a molecular junction structure on Au(111).The electronic properties of the structure are studied by scanning tunneling spectroscopy(STS)combined with tight binding(TB)calculations.The pentagon ring junction shows a weak electronic coupling effect on graphene nanoribbons,which makes the electronic properties of the two different graphene nanoribbons connected by a pentagon ring junction analogous to type I semiconductor heterojunctions.

Progress of hidden spin polarization in inversion-symmetric crystals

Hidden spin polarization refers to that doubly degenerate bands protected by combined inversion and time-reversal symmetry in nonmagnetic inversion-symmetric crystals could have opposite non-zero local spin polarizations, which are spatially separated in two real-space sectors paired by the inversion symmetry. Since its first prediction from ab initio calculation, hidden spin polarization has inspired tremendous interest and has been observed experimentally due to its intriguing fundamental properties as well as the great potential for applications. Moving forward, the search for moment-dependent spin splitting has also been extended to antiferromagnets even without considering spin-orbit coupling. This paper systematically reviews recent works in this field with a focus on basic concepts and material realization. It also details several remaining bottlenecks and suggests possible avenues for future research.

The band structures of some transition metals and their NaCl-type compounds

The band structures of Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta) and VIE (Cr, Mo, W) transition metals and some of their carbides and nitrides (TiN, ZrN, HfN, VC, NbC, TaC, VN, NbN, TaN) with NaCl-type (B1-type) structure have been calculated by using the tight-binding method within the Extended Huckel approximation (EHT). The energy bands, densities of states and crystal orbital overlap populations are given. The relationship between the bonding properties and the superconducting transition temperatures (T-c) of them is discussed. The influences of various kinds of metallic atoms and changes of bond lengths on T-c are also discussed.