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The electronic structure of Ti8C12 clusters with three possible geometric structures suggested in the literature is studied using the discrete-variational local-density-functional method. The results show that the ground states of the clusters are all degenerate, which means further Jahn-Teller distortions for the geometric structures of clusters. The results also indicate that the distorted dodecahedral Ti8C12 cluster, which is proposed by Guo et al. and optimized by the first principle calculations, is the most stable one among the clusters we considered and its electronic structure can explain the experimental observations. In this cluster, there is a strong pd bonding between Ti and C atoms, and the density of states at the Fermi energy is high. 相似文献
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用赝势从头计算方法研究Hf8C12多面体.先对T和Td分子构型作几何优化,发现Td对称构型比T构型稳定.利用非限制的Hartre Fock方法及自然键轨道分析研究Td构型的Hf8C12基团,结果表明:Hf8C12存在三种自旋不同的基态,这种基态的多样性与成键机制、电子组态和电子能谱分布密切相关.其中S=0时,Hf8C12主要是由外四面体Hf原子与类乙烯C2单元形成极性共价键构成.S=1时,6个类乙炔C2单元吸附在Hf8金属框架.S=2时,部分C2中的pπ键断裂与Hf原子形成d←pπ键.进一步分析发现,Td对称性的结构模型为(Hf8)+4.5(C-0.752)6,在高自旋态下具有铁磁性,电子能级分布及其能隙随自旋态而变化.
关键词: 相似文献
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The electronic structures and geometry of a solid assembled out of cubic close packing of Al12Si clusters have been studied with an ab initio pseudopotential method and within the local density functional theory. Both the lattice constant of the solid formed and the atomic geometry of the clusters in it have been optimized through the ab initio method without adjustable variables. Our results show that the crystal composed of Al12Si clusters is a metal rather than a semiconductor. Interactions between Al12Si clusters in the solid are strong and the clusters are no longer inert under crystal field. 相似文献
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The electronic structures of the perovskite oxides, LaMnO3 and CaMnO3, with various magnetic structures are studied using the first-principles discrete variational (DV) cluster method based on ab initio local-spin-density approximation (LSDA). The ground states of different magnetic phases (including ferromagnetic (FM), A-type antiferromagnetic (A-AFM), and G-type antiferromagnetic (G-AFM)) have been described in this work. The cubic CaMnO3 with observed G-AFM magnetic order is found to have a 0.1 eV calculated gap. Both FM CaMnO3 and LaMnO3 have "half-metallic" character, which is in agreement with other works. LaMnO3 with both A-type and G-type antiferromagnetic order have metallic band structures. Part of Jahn-Teller (JT) distortion (Q2 type) has been taken into consideration for A-AFM LaMnO3. Under Q2 type JT distortion, the occupied and unoccupied states of O 2p and Mn 3d states move farther away from the Fermi energy. It is also found that the distortion can further stabilize the structure. The density of states and the binding energy of the distorted A-AFM LaMnO3 are given in this paper. 相似文献
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用自洽LMTO-ASA方法研究了ScH2及HfH2的电子结构,毋需在面心晶格的八面体中心位置上加入一个额外的球作为muffin-tin势的修正,关于ScH2本结果与Peterman及Harmon的计算结果及光电子谱结果十分一致;除去21的位置处在Fermi能级之下,因而在ScH2中H也可能占据八面体位置。HfH2状态密度的大致轮廓定性上与光电子谱结果是符合的。H原子带有1.2—1.3个电子电荷。
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Wenxia Feng Haiquan Hu Shouxin Cui Guiqing Zhang Zengtao Lv Cheng Wu 《Solid State Communications》2011,151(21):1564-1567
The structural, electronic and elastic properties of Ti3Si0.5Ge0.5C2 have been investigated by using the pseudopotential plane-wave method within the density-functional theory. Our calculated equation of state (EOS) is consistent with the experimental results. The density of states (DOS) indicates that Ti3SixGe1−xC2 (x=0, 0.5, 1.0) are metallic, and these compounds have nearly the same electrical conductivity. The elastic constants for Ti3Si0.5Ge0.5C2 are obtained at zero pressure, which is compared to Ti3SiC2 and Ti3GeC2. We can conclude that Ti3Si0.5Ge0.5C2 is brittle in nature by analyzing the ratio between bulk and shear moduli. There appears to be little effect on the electronic and elastic properties with the Ge substitution to Si atoms in Ti3SiC2. 相似文献
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采用基于密度泛函理论的相对论性离散变分和嵌入团簇方法模拟计算了PbWO4晶体的本征能级结构.发现价带主要由O2p轨道组成,含有部分W5d轨道;导带主要由W5d和O2p的轨道组成.发现导带底由Pb6p1/2的狭窄能级占有.禁带宽度和价带宽度分别约为4.8和4eV.计算结果很好地解释了实验得到的反射谱,并从理论上分析了PbWO4晶体蓝光的发光模型.
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密度泛函
电子结构
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The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron
density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor
clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12 are calculated using the ab initio Hartree-Fock method in the 6–31G basis set.
Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3,
pp. 535–542. 相似文献
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本文研究了TbFe2非晶态薄膜的磁性和电性,测量了Ms(T)(77—800K),ρ(T)(4.2—400K)和穆斯堡尔谱(18K,400K),得到居里温度Tc~400K,电阻极小值温度Tmin~360K,在T<360K范围内观察到温度系数为负的类Kondo效应,用Hesse和Window两种不同方法解出了室温穆斯堡尔谱的超精细场,得到了H=210kOe和H=25kOe两种分布,其中前一组给出了铁磁性,后一组可能与类Ko
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We discuss the validity of Migdal–Eliashberg theory applied to the superconductor fullerides K3C60 and Rb3C60. Recently, the relevant superconductor properties have been measured, like the isotope coefficient, the energy gap and critical temperatures for these compounds and compared with their optical properties. They all present a very disperse band of phonon frequencies, running from very small to very large energies, the latter being close to the Fermi edge. Therefore, these materials exceed the limit of validity of the adiabatic Migdal theorem, measured with a nonadiabatic parameter m=w0/EF, where w0 is a characteristic phonon frequency and EF=250 meV, the Fermi level. We examine previous theories incorporating vertex corrections into the Eliashberg equations to deal with such a situation. We compare these approaches by calculating the critical temperatures using a multimodal Eliashberg spectral function 2F(w) to study the contribution of the various phononic modes. We arrive at the conclusion that the optical modes, not the intramolecular ones, are among those which maximize Tc independently of including vertex corrections or not. This result goes in the direction to understand why doped fullerides A3C60 are superconductors. 相似文献
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The structural, elastic, and electronic properties of a series of icosahedral phases, such as boron subcarbides B12C3 and B13C2, subnitride B12N2, and suboxide B12O2, have been studied in the framework of the SCC-DFTB method. It has been found that the B12C2 and B13C2 phases manifest metal-like properties, while B12C3 and B12O2 are semiconductors. The estimates have shown that the insertion of 2p atoms (C, N, or O) into intericosahedral pores of elemental boron can cause both a decrease in its elastic modulus (an increase
in the compressibility of B12N2) and a sharp increase in the modulus B (in subcarbides B12C3 and B12BCC). On the other hand, the insertion of 2p atoms into α-B12 will favor an increase in its hardness (suboxide B12O2 will have a maximum hardness). 相似文献