低对称层状ReS2的电子结构和各向异性光学性质研究

采用第一性原理赝势平面波方法计算了三斜晶系低对称层状半导体二硫化铼（ReS2）的晶体结构、电子结构及光学性质。结果表明：扭曲的1T结构为ReS2的稳定结构, Re原子与其周围的S原子形成六配位的近似八面体结构,Re-S键长最大偏差为8.3%,Re-S键布局数最大偏差为40.5%,表明ReS2结构的低对称性;ReS2为直接带隙半导体,费米面附近的价带和导带主要由Re的5d及S的3p轨道电子构成,其中Re的5d轨道电子的贡献最大;当入射偏振光沿着[100]和[010]方向时,介电函数的实部（或虚部）非常接近,而当入射偏振光沿[001]方向时,介电函数的实部（及虚部）表现出明显的各向异性,主要是由于ReS2的结构低对称性和弱层间耦合造成的。     

Structural, electronic and phonon properties’ investigation of YP and YAs compounds

We have studied the structural, electronic and phonon properties of the YP and YAs compounds in NaCl(B1) and CsCl(B2) structures using the density functional theory within the generalized gradient approximation (GGA). The calculated lattice constants, static bulk modulus, first-order pressure derivative of the bulk modulus and transition pressure are reported and compared with previous calculations. We have carried out the calculations of band structure and density of states (DOS) for YP and YAs. Then, a linear-response approach to the density-functional theory is used to derive the phonon frequencies and DOS in both B1 and B2 structures.     

丙烯腈单体自由基反应及光谱分析的研究

采用密度泛函理论对以偶氮二异丁腈为引发剂形成的丙烯腈单体自由基(CH₃)₂(CN)C—CH₂—(CN)CH的终止方式反应机理进行研究。先用B3LYP/6-31G(d)基组对反应物、偶合中间体、过渡态、歧化产物的几何构型进行优化,并计算了各物种经过零点能校正后的总能量,红外频率和电子结构,同时对过渡态结构进行了验证。研究结果表明,反应物先通过自由基的偶合终止方式形成偶合中间体a,再由此经过氢迁移、裂解等机理得到歧化终止产物P[p₁(CH₃)₂(CN)CCHCHCN+p₂(CH₃)₂(CN)C—CH₂—CH₂CN]。双自由基发生偶合和歧化终止反应分别形成偶合中间体a和歧化终止产物P均为放热反应,且偶合产物有着更低的能量。反应过程的速控步骤a→TS→P在常温下的速率常数表示为k(298.15 K)=2.71×10-59。歧化终止反应随着反应温度的升高易于进行,歧化产物所占的比例也增加。通过对反应过程各物种红外谱图的分析,说明自由基在整个终止反应的化学变化,同时分析了HOMO-LUMO电子密度分布的信息,验证丙烯腈双自由基偶合终止方式和各物种结构的准确性。     

Structural and electronic properties of ZnO under high pressures

In this work, we use first-principles calculations based on density-functional theory within the local-density approximation (LDA) to investigate the structural and electronic properties of ZnO under high-pressure. We have calculated the ground-state energy, the lattice constant, the bulk modulus, and its pressure derivative of the B4 (wurtzie), B3 (zinc blende), B2 (CsCl) and B1 (rocksalt) phases of ZnO. Moreover, the electronic structure, density of states (DOS) of the B4 (wurtzite) and B1 (rocksalt) phases of ZnO have been calculated. We show that our calculated values compare acceptably well with values reported in the literature.     

Theoretical studies on the high pressure phases of Lanthanum monochalcogenides

We report total energy and electronic structure calculations for lanthanum monochalcogenides in B1 (NaCl) and B2 (CsCl) crystal structures over a range of unit cell volumes. We employed the tight binding linear muffin-tin orbital approach to density functional theory within the local density approximation to expand the crystal orbitals and periodic electron density. In agreement with the experiment we find that B1 phase is lower in energy than B2 phase, and that the compounds transforms to B2 structure under applied pressure. This is the first qualitative prediction of the transition in La monochalcogenides and should be testable with diamond-anvil technique.     

Structural and electronic properties of Bin (n = 2-14) clusters from density-functional calculations

The structural and electronic properties of Bi_n (n = 2-14) clusters have been systematically studied using gradient-corrected density-functional theory. For each cluster size, a number of structural isomers were constructed and optimized to search for the lowest-energy structure. The competition of several structural patterns such as cages, superclusters, and layered structures leads to the alternating appearance of these configurations as global minima. Although the tendency of Bi to form puckered-layer structures is already well-known, the electronic states of Bi_n clusters are still far from that of the bulk. As well, a remarkable even-odd atom number oscillation is observed in the structural and electronic properties of the clusters, implying that the stability of Bi_n clusters is mainly dominated by the electron shell effect rather than by geometrical packing. The theoretically calculated values for electron affinities agree well with available experimental data.     

Density functional predictions of new silicon allotropes: Electronic properties and potential applications to Li-battery anode materials

In terms of first-principles density functional calculations, we investigate the stabilities and electronic properties of two hypothetical allotropes of silicon, the body-centered tetragonal (Bct) and monoclinic (M4) phases. The calculated electronic structures and phonon dispersions reveal that both phases are stable and have a band gap smaller than that of the diamond form of silicon by a factor of ∼2. We also discuss the possible applications of Bct and M4 phases as lithium-battery anode material.     

AunLa(n=1-8)团簇的密度泛函研究

采用密度泛函理论（DFT）中的杂化密度泛函B3LYP方法,在LANL2DZ基组水平上研究了AunLa (n=1-8)团簇的几何结构。计算并讨论了基态结构稳定性及电子性质。结果表明,当n=3-8时,基态结构均为三维结构且La原子趋向与更多的Au原子结合。团簇二阶能量差分,能隙和化学硬度计算结果显示除了AuLa外,具有偶数数目的团簇比奇数数目的团簇具有更好的稳定性,其中,Au3La团簇的稳定性相对较好。     

AunLa(n=1~8)团簇的密度泛函研究简

采用密度泛函理论(DFT)中的杂化密度泛函B3LYP方法,在LANL2DZ基组水平上研究了Aun La(n=1~8)团簇的几何结构.计算并讨论了基态结构稳定性及电子性质.结果表明,当n=3-8时,基态结构均为三维结构且La原子趋向与更多的Au原子结合.团簇二阶能量差分,能隙和化学硬度计算结果显示除了AuLa外,具有偶数数目的团簇比奇数数目的团簇具有更好的稳定性,其中,Au3La团簇的稳定性相对较好.     

3C-SiC材料p型掺杂的第一性原理研究

采用基于第一性原理的密度泛函理论平面波超软赝势法,研究了SiC材料p型掺杂的晶体结构和电子结构性质,得到了优化后体系的结构参数,掺杂形成能,能带结构和电子态密度,计算得到掺杂B,Al,Ga在不同浓度下的禁带宽度.结果表明:随着掺杂B原子浓度的增大,禁带宽度随之减小;而随着掺杂Al,Ga原子浓度的增大,禁带宽度随之增大;在相同浓度下,掺杂Ga的禁带宽度大于掺杂Al,掺Al禁带宽度大于掺B. 关键词： SiC 电子结构 掺杂 第一性原理软件     

First-principle study of structural and electronic properties of ternary layered Ta2AlC

The structural and electronic properties of ternary layered Ta₂AlC ceramics have been studied using the first-principle method based on the density-functional theory. We have obtained the equilibrium lattice parameters and the equilibrium atomic positions in the unit cell. The equilibrium lattice parameters are computed to be a=b=3.15 Å and c=13.95 Å. The internal coordinates of Ta are determined to be (1/3, 2/3, 0.092). The band structure and density of states reveal that Ta₂AlC is an electronic conductor. The charge density distribution shows that the Ta and C atoms form a strong Ta-C-Ta covalently bonded chain.     

密度泛函理论研究Nb_2Ge_n(n=1～4)团簇

运用密度泛函方法在(U)B3LYP/Lan L2DZ水平上对Nb_2Ge_n(n=1~4)团簇进行了系统的理论研究,得到Nb_2Ge_n(n=1~4)团簇的最低能结构的几何构型和电子性质.优化结果表明:Nb_2Ge_n(n=1~4)团簇最低能结构的自旋多重度均为单重态.团簇最低能结构的电子态与团簇的大小有关.当n为奇数时,团簇的电子态为~1A~1,n为偶数时电子态为1A.通过对计算平均束缚能和分裂能发现:Nb_2Ge_n(n=1~4)团簇中热力学稳定性最强的是Nb_2Ge_2团簇;最弱的是Nb_2Ge_4团簇.自然电荷分布的结果说明Nb_2Ge_n(n=1~4)团簇中当n=1-2时,电子转移正常,而当n=3-4时出现电荷反转现象.同时还研究了HOMOLUMO能隙、磁性和红外光谱.     

Ab initio study of the electronic structure and the magnetic properties of polymers Co[N(CN)2]2(L) [L=pyrazine dioxide (pzdo) and 2-methyl pyrazine dioxide (mpdo)] with dual μ- and μ3-[N(CN)2] bridges

The first principle within the full potential linearized augmented-plane-wave (FP-LAPW) method was applied to study the compound of Co[N(CN)₂]₂(L) [L=pyrazine dioxide (pzdo) and 2-methyl pyrazine dioxide (mpdo)] with dual μ- and μ₃-[N(CN)₂]⁻ bridges. The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that these two compounds have a ferromagnetic (FM) interaction arising from the 1,5-μ- and μ₃-[N(CN)₂]⁻ bridges. The spin magnetic moment mainly comes from the Co ion with little contribution from N, O and C anions.     

立方晶相HfO2电子结构与光学性质的第一性原理计算

利用密度泛函理论框架下的第一性原理平面波超软赝势方法计算了立方晶相二氧化铪(c-HfO2)的电子结构,得到了c-HfO2的总念密度、分波态密度和能带结构.经带隙校正后,计算了c-HfO2的光学线性响应函数随光子能最的变化关系,包括复介电函数,反射率、复折射率以及光学吸收系数,并从理论上给出了c-HfO2材料光学性 质与电子结构的关系.经比较发现,对c-HfO2的电子结构和光学性质的计算结果与已有的实验数据和其它理论研究吻合得较好,从而为c-HfO2光电材料的设计与应用提供了理论依据.同时,计算结果也表明采用密度泛函理论的广义梯度近似来计算和预测c-HfO2材料的电子结构和光学性质是比较可靠的.     

First principles calculations of structural,electronic and optical properties of various phases of CaS

First principles calculations have been performed within the framework of density functional theory to investigate the structural, electronic and optical properties of all four possible B1, B2, B3 and B4 phases of CaS. Apart from the standard local density approximation (LDA) and GGA (PBE), a more accurate nonempirical density functional generalized gradient approximation (GGA), as proposed by Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] for the exchange-correlation energy, E_XC, has been attempted in these calculations. Calculated electronic structure and the density of states are analyzed in terms of the contribution of Ca d states and S s and p states in determining the nature of the fundamental band gap in various phases. Reflectivity, R (ω), the real and imaginary part of the dielectric functions, ε(ω), have been calculated for all the phases and the results have been discussed and compared with the existing experimental data.     

F掺杂SnO2电子结构的模拟计算

采用基于密度泛函理论的平面波赝势方法对SnO₂:F体系的电子结构进行了第一性原理模拟计算.用广义梯度近似方法优化SnO₂:F体系的晶胞结构，计算了体系基态总能.通过确定F掺杂对O的优先替代位置，计算了SnO₂:F的能带结构、态密度、分波态密度.分析了F掺杂对SnO₂晶体的电子结构和晶体性质及光学吸收边的影响，从理论上得出光学吸收边发生蓝移.对不同掺杂量的体系电子结构进行了分析. 关键词： F掺杂 2')" href="#">SnO₂ 电子结构 态密度     

First principles lattice dynamical calculation of semiboride Be2B and its ternary alloys XBeB (X=Na, Mg, Al)

We present results of first principles total energy calculations of the structure, electronic and lattice dynamics for beryllium semiboride and its three ternary alloys using generalized gradient and local density approximations under the framework of density functional theory. The generalized gradient approximation is used for all compounds except MgBeB using the Perdew-Burke-Ernzehorf exchange correlation functional while local density approximations use the Perdew-Zunger ultrasoft exchange correlation functional. The calculated ground state structural parameters are in good agreement with those of experimental and previous theoretical studies. The electronic band structure calculations show that Be₂B may transform to a semiconductor after Al substitution. A linear response approach to density functional theory is used to calculate phonon dispersion curves and vibrational density of states. The phonon dispersion curves of Be₂B and AlBeB are positive indicating a dynamical stablility of the structure for these compounds. The phonon dispersion curves of NaBeB and MgBeB show the imaginary phonons throughout the Brillouin zone, which confirms dynamical instability as indicated in band structures for these alloys. We also present the partial phonon density of states for different species of Be₂B and AlBeB to bring out the details of the participation of different atoms in the total phonon density of state, particularly the role played by Al atom. The first time calculated phonon properties are clearly able to bring out the significant effect of isoelectronic substitution in Be₂B.     

Magnetic phase diagram in a quasi-two-dimensional electron gas

Using spin density functional theory within the framework of the local spin density approximation with Perdew-Zunger type exchange-correlation energy, ferromagnetism in a quasi-two-dimensional electron gas (Q-2DEG) is studied. The electronic and magnetic structures of a thin film are calculated as a function of film thickness and electron density. Ferromagnetism in the Q-2DEG is found to appear at a higher electron density than in the three-dimensional electron gas. Unless a film is very thin, with decreasing electron density, a magnetic phase transition occurs from a spin-unpolarized fluid to a Wigner film with surface magnetism, in which the spin polarization localizes only in the neighborhood of surfaces. Further decreasing density induces another transition to a fully spin-polarized ferromagnetic Wigner film.     

The stabilities, electronic structures and elastic properties of Rb-As systems

The structural, electronic and elastic properties of Rb–As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3 As in Na3As, Cu3 P and Li3Bi structures, and Rb5 As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghan’s equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young’s modulus, the shear modulus, Poisson’s ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.     

Ab initio study of the electronic structures and conduction properties of some novel low band-gap donor-acceptor polymers

The results of the electronic structures and conduction properties of four novel donor-acceptor polymers based on polysilole, obtained on the basis of ab initio Hartree-Fock crystal orbital method using their optimized geometries, are reported. The repeat unit of these polymers consists of bicyclopentadisilole unit bridged by an electron-accepting group Y(Y=CCH₂ in PSICH, CO in PSICF, CCF₂ and CC(CN)₂ in PSICN). All the polymers on the basis of their geometries and π-bond order values are found to have benzenoid-type electronic structures. Comparison of the important electronic properties such as ionization potential, electron affinity and band-gap of these polymers indicates PSICN to be the best candidate for intrinsic conductivity and reductive (n-) doping while PSICH is predicted to be the best candidate for oxidative (p-) doping. All these polymers are estimated to have band-gap values ranging between 1 and 2 eV. The low band-gap values of these polymers are rationalised on the basis of the patterns of their frontier orbitals.