共查询到19条相似文献,搜索用时 171 毫秒
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在面心立方(fcc)、体心立方(bcc)和六角密堆积(hcp)3种不同结构晶体的自由电子能带模型中,发现4个最低能带与5个次低能带本征值的平均能量(称为平均键能,Em)与费米能级(EF)相当接近;并进一步在hcp结构的钛(Ti)、锆(Zr)和铪(Hf)以及bcc结构的铁(Fe)等金属中,采用从头赝势能带计算方法和平均键能计算方法,证实在这些金属的实际能带中,平均键能(Em)值仍然非常接近于费米能级(EF)值.该发现有助于进一步了解平均键能(Em)的物理内涵.
关键词:
平均键能
费米能级
能带结构 相似文献
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用自洽的全势能线性丸盒轨道能带方法计算了氧化物体系SrRuO3(SRO)的电子结构和磁性 .对于理想的立方钙钛矿结构的计算得出的电子结构明显改善了已有的计算结果 :每个元胞的磁矩为 1 2 9μB ,按原子球划分为 0 84μB Ru原子和 0 11μB O原子 ;Sr原子上的自旋磁矩几乎为零 ;费米能级处的态密度N(EF)为 4 3 5 (states Ryd f.u .) .关于实际的正交结构SRO ,计算得出磁矩为 1 0 8μB f.u .的铁磁性基态 ,费米能级处的态密度N(EF)为 61 0(states Ryd f.u .) ,电子线性比热系数γ为 10 60mJ mol·K2 .结果说明SRO是一宽能带的巡游铁磁性体系 . 相似文献
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采用基于密度泛函理论的平面波赝势方法和广义梯度近似,对未掺杂、掺B、掺N的碳纳米管(CNT)不同位置上Al原子的吸附进行了几何优化,计算了吸附Al、掺杂前后CNT的能带结构、态密度、差分电荷密度、电荷布居数和吸附能.计算结果表明,掺B使CNT形成缺电子状态,利于具有自由电子的Al原子的吸附结合,可显著提高Al在金属性的(5,5)CNT和半导性的(8,0)CNT外壁的吸附能;掺杂N形成多电子状态,在费米能级附近半满的施主能级也利于填充Al的价电子,改善Al在(5,5)CNT和(8,0)CNT外壁的吸附结合性
关键词:
密度泛函理论
单壁碳纳米管
B(N)掺杂
Al原子吸附 相似文献
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采用不同方法B3P86,B3LYP,MP2和LSDA,结合Dunning的相关一致基组cc-PVTZ,对聚合型硼氢化物(BH3)n(n=1—3)分子的可能几何构型进行优化计算,得出最稳定构型的几何参数、电子结构、振动频率和光谱等性质参数,并给出了最稳定结构的总能量(ET),结合能(EBT),平均结合能(Eav),电离势(EIP),能隙(Eg),费米能级(EF)等.结果表明:采用密度泛函DFT中的方法B3P86计算的能量最低,结构参数更接近文献值;三种硼氢化物分子基态都为1重态,电子态分别为1A',1A和1A;BH3分子的最稳定几何构型为平面三角形结构;B2H6为对称性乙烯式D2h立体结构,H—B之间生成氢桥式三中心双电子键;B3H9为C3ν立体结构,也生成氢桥式三中心双电子键,但三个氢桥三中心双电子键彼此隔离.最后分析了三种氢化物的红外和拉曼光谱、平均结合能、电离势、能隙和费米能级等特性,说明(BH3)n(n=1—3)三分子中B2H6最稳定,H—B桥键键长比端键更长,最强峰红外光谱强度最大. 相似文献
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采用不同方法B3P86、B3LYP、B3PW91和MP2,结合Dunning的相关一致基组cc-PVTZ,对聚合型铝氢化物(AlH3)n(n=1-3)分子的可能几何构型进行优化计算,通过比较计算结果,发现密度泛函DFT中的方法B3P86计算的能量最低.本文采用B3P86方法得出最稳定构型的几何参数、电子结构、振动频率等性质参数,并给出最稳定结构的总能量(ET)、结合能(EBT)、平均结合能(Eav)、电离势(EIP)、能隙(Eg)、费米能级(EF)和差分吸附氢原子能(Ediff).结果表明:三种铝氢化物分子基态都为1重态,电子态都为 ; AlH3分子的最稳定几何构型为 的平面三角形结构;Al2H6为对称性乙烯式 立体结构,H-Al之间生成氢桥式三中心双电子键;Al3H9为 立体结构,也生成氢桥式三中心双电子键,但三个氢桥三中心双电子键彼此隔离.最后分析了三种氢化物的红外和拉曼光谱、平均结合能、电离势、能隙和费米能级等特性,说明(AlH3)n(n=1-3)三分子中Al3H9最稳定,H-Al桥键键长比端键更长,红外光谱强度最大,差分吸附氢原子能最大,具有较强的储氢性能. 相似文献
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聚合型铝氢化物(AlH3)n(n=1-3)的几何结构与振动光谱的研究 总被引:1,自引:0,他引:1
采用不同方法B3P86、B3LYP、B3PW91和MP2,结合Dunning的相关一致基组cc-PVTZ,对聚合型铝氢化物(AlH3)n(n=1-3)分子的可能几何构型进行优化计算,通过比较计算结果,发现密度泛函DFT中的方法B3P86计算的能量最低.本文采用B3P86方法得出最稳定构型的几何参数、电子结构、振动频率等性质参数,并给出最稳定结构的总能量(ET)、结合能(EBT)、平均结合能(Eav)、电离势(EIP)、能隙(Eg)、费米能级(EF)和差分吸附氢原子能(Ediff).结果表明:三种铝氢化物分子基态都为1重态,电子态都为 ; AlH3分子的最稳定几何构型为 的平面三角形结构;Al2H6为对称性乙烯式 立体结构,H-Al之间生成氢桥式三中心双电子键;Al3H9为 立体结构,也生成氢桥式三中心双电子键,但三个氢桥三中心双电子键彼此隔离.最后分析了三种氢化物的红外和拉曼光谱、平均结合能、电离势、能隙和费米能级等特性,说明(AlH3)n(n=1-3)三分子中Al3H9最稳定,H-Al桥键键长比端键更长,红外光谱强度最大,差分吸附氢原子能最大,具有较强的储氢性能. 相似文献
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采用第一性原理的密度泛函理论赝势平面波方法,计算了未掺杂与B、N单掺杂3C-SiC的电子结构和光学性质.结果表明:掺杂改变了3C-SiC费米面附近的电子结构;B掺杂使得禁带宽度减小,价带顶上移,费米能级进入价带,形成p型半导体;N掺杂使得禁带宽度减小,导带底下移,费米能级进入导带,形成n型半导体.B、N掺杂均提高了3C-SiC在低能区的折射率、消光系数和吸收系数,增强了对红外光谱的吸收. 相似文献
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通过第一性原理计算研究了具有锯齿状边沿并且具有反铁磁构型的单层石墨纳米带的自旋极化输运.研究发现,在中心散射区同一位置掺入单个B和N原子,尽管对整个体系磁矩的影响完全相同,但对两个自旋分量电流的影响却完全相反.掺B时,自旋向上的电流显著大于自旋向下的电流;而掺N时,自旋向下的电流显著大于自旋向上的电流.这是由于不管掺B还是掺N都将打破自旋简并,使得导带和价带中自旋向上的能级比自旋向下的能级更高.掺B引入空穴,使完全占据的价带变为部分占据,从而自旋向上的能级正好处于费米能级,使得电子透射能力更强、电流更大,而自旋向下的能级则离费米能级较远使电子透射的能力较弱.掺N则引入电子,使得原来全空的导带变为部分占据,从而费米能级穿过导带中自旋向下的能级,使得自旋向下的电子比自旋向上的电子透射能力更强.
关键词:
自旋极化输运
单层石墨纳米带
第一性原理
非平衡格林函数 相似文献
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Intrinsic electron accumulation at clean InN surfaces 总被引:1,自引:0,他引:1
The electronic structure of clean InN(0001) surfaces has been investigated by high-resolution electron-energy-loss spectroscopy of the conduction band electron plasmon excitations. An intrinsic surface electron accumulation layer is found to exist and is explained in terms of a particularly low Gamma-point conduction band minimum in wurtzite InN. As a result, surface Fermi level pinning high in the conduction band in the vicinity of the Gamma point, but near the average midgap energy, produces charged donor-type surface states with associated downward band bending. Semiclassical dielectric theory simulations of the energy-loss spectra and charge-profile calculations indicate a surface state density of 2.5 (+/-0.2)x10(13) cm(-2) and a surface Fermi level of 1.64+/-0.10 eV above the valence band maximum. 相似文献
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Ying-bo Lv Ying Dai Kesong YangZhenkui Zhang Wei WeiMeng Guo Baibiao Huang 《Physica B: Condensed Matter》2011,406(20):3926-3930
Recent experiments reported fascinating phenomenon of photoluminescence (PL) blueshift in Ge-doped ZnO. To understand it, we examined the structural, electronic and optical properties of Ge-doped ZnO (ZnO:Ge) systematically by means of density functional theory calculations. Our results show that Ge atoms tend to cluster in heavily doped ZnO. Ge clusters can limit the conductivity of doped ZnO but reinforce the near-band-edge emission. The substitutional Ge for Zn leads to Fermi level pinning in the conduction band, which indicates Ge-doped ZnO is of n-type conductivity character. It is found that the delocalized Ge 4s states hybridize with conduction band bottom, and is dominant in the region near the Fermi level, suggesting that Ge-4s states provides major free carriers in ZnO:Ge crystal. The observed blueshift of PL in Ge-doped ZnO originates from the electron transition energy from the valence band to the empty levels above Fermi level larger than the gap of undoped ZnO. The electron transition between the gap states induced by oxygen vacancy and conduction band minimum may be the origin of the new PL peak at 590 nm. 相似文献
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SCF-Xα SW MO calculations on metal core ion hole states and X-ray emission (XES) and X-ray photoelectron (XPS) transition states of the non- transition metal oxidic clusters MgO610?, AlO45? and SiO44? show relative valence orbital energies to be virtually unaffected by the creation of valence orbital or metal core orbital holes. Accordingly, valence orbital energies derived from XPS and XES are directly comparable and may be correlated to generate empirical MO diagrams. In addition, charge relaxation about the metal core hole is small and valence orbital compositions are little changed in the core hole state. On the other hand, for the transition metal oxidic clusters FeO610?, CrO69? and TiO68? relative valence orbital energies are sharply changed by a metal core orbital or crystal field orbital hole, the energy lowering of an orbital increasing with its degree of metal character. Consequently O 2p nonbonding → M 3d-O 2p antibonding (crystal field) energies are reduced, while M 3d bonding → O 2p nonbonding and M 3d-O 2p antibonding → M 4s,p-O 2p antibonding (conduction band) energies increase. Charge relaxation about the core hole is virtually complete in the transition metal oxides and substantial changes are observed in the composition of those valence orbitals with appreciable M 3d character. This change in composition is greater for e g than for t2g orbitals and increases as the separation of the eg crystal field (CF) orbitals and the O 2p nonbonding orbital set decreases. Based on the hole state MO diagrams the higher energy XPS satellite in TiO2 (at about 13 eV) is assigned to a valence → conduction band transition. The UV PES satellites at 8.2 eV in Cr2O3 and 9.3 eV in FeO are tentatively assigned to similar transitions to conduction band orbitals, although the closeness in energy of the crystal field and O 2p nonbonding orbitals in the valence orbital hole state prevents a definite assignment on energy criteria alone. However the calculations do clearly show that charge transfer transitions of the eg bonding → eg crystal field orbital type would generally occur at lower energy than is consistent with observed satellite structure.A core electron hole has little effect upon relative orbital energies and is only slightly neutralized by valence electron redistribution for MgO and SiO2. For the transition metal oxides a core hole lowers the relative energies of M3d containing orbitals by large amounts, reducing O → M charge transfer and increasing M 3d crystal field → conduction band energies. Large and sometimes overcomplete neutralization of the core hole is observed, increasing from CrO69? to FeO610? to TiO68?. as the O → M charge transfer energy declines.High energy XPS satellites in TiO2 may be assigned to O 2p nonbonding → conduction band transitions while lower energy UV PES satellites in FeO and Cr2O3 arise from crystal field or O 2p nonbonding → conduction band excitations. Our “shake-up” assignment for FeO610?, CrO69? and TiO68? are less than definitive because no procedure has yet been developed to calculate “shake-up” intensities resulting from transitions of the type described. However the results do allow a critical evaluation of earlier qualitative predictions of core and valence hole effects. First, we find that the comparison of hole or valence state ionic systems with equilibrium distance systems of higher nuclear and/or cation charge (e.g. the comparison of the FeO610? Fe 2p core hole state to Co3O4) is dangerous. For example, larger MO distances in the ion states substantially reduce crystal field splittings. Second, core and CF orbital holes sharply reduce O → M charge transfer energies, giving 2eg → 3eg energy separations which are generally too small to match observed satellite energies. Third, highest occupied CF-conduction band energies are only about 4–5 eV in the ground states, but increase to about 7–11 eV in the core and valence hole states of the transition metal oxides studied. The energetic arguments presented thus support the idea of CF and/or O 2p nonbonding → conduction band excitations as assignments for “shake-up” satellites, at least in oxides of metals near the beginning of the transition series. 相似文献
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采用基于密度泛函理论的第一性原理分析方法的CASTEP软件,计算了Ni、C单掺杂和共掺杂SnO2的晶格参数、能带结构、电子态密度和布局,结果表明:单掺杂和共掺杂均使得晶胞体积略微增大,禁带减小,且仍属于直接带隙半导体,在价带顶和导带底产生杂质能级,其中Ni-C共掺杂时禁带最小,杂质能级最多,电子跃迁需要的能量更小,导电性也就最好.共掺杂时费米能级附近的峰值有所减小,局域性降低,原子间的成键结合力更强,使得SnO2材料也更加稳定. 相似文献
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本文采用基于第一性原理的密度泛函理论超软雁势平面波方法,对铁磁性半导体高锰硅化合物Mn_4Si_7进行了理论计算.结果表明块体Mn_4Si_7是准直接带隙半导体材料,其价带主要是由Mn的3d轨道电子构成,导带主要是由Mn的3d及Si的3p轨道电子构成.相同自旋轨道下,自旋向下态的电子更容易占据较高的能级.而自旋向上态的电子对Mn_4Si_7的禁带宽度起主导作用. Mn_4Si_7的费米能级附近各轨道未被电子占满,且自旋向上态与自旋向下态电子的不对称分布使其具有了磁性.为Mn_4Si_7磁学特性提供主要贡献的是Mn的3d轨道电子,而Si的3p和3s轨道电子提供了一个小的贡献. 相似文献
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The optical, electrical, and chemical properties of semiconductor surfaces are largely determined by their electronic states close to the Fermi level (E{F}). We use scanning tunneling microscopy and density functional theory to clarify the fundamental nature of the ground state Ge(001) electronic structure near E{F}, and resolve previously contradictory photoemission and tunneling spectroscopy data. The highest energy occupied surface states were found to be exclusively back bond states, in contrast to the Si(001) surface, where dangling bond states also lie at the top of the valence band. 相似文献