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1.
采用基于密度泛函理论中的广义梯度近似的第一性原理研究, 优化了纤锌矿结构化合物CrX(X=As、Sb、O、Se和Te)的几何结构, 并详细计算了它们的磁电性能. 结果表明, 这些磷族或硫族化合物在费米面处的自旋极化率均为100%, 分子磁矩分别为整数3.00和4.00 μB; 分子磁矩主要来自于Cr离子; 磷族和硫族化合物中存在亚铁磁性耦合; 它们的居里温度均较高; 磷族和硫族化合物中Cr离子的电子结构分别为a21g↑↓t41u↑↓t11u↑e2g↑和a21g↑↓t41u↑↓t11u↑t32g↑.  相似文献   

2.
基于第一性原理方法结合广义梯度近似,研究了分子基磁体Cr[N(CN)2]2的电子结构和半金属性. 对总能量,自旋极化的能带结构,态密度以及自旋磁矩的计算表明该分子磁体为半金属铁磁体.每个分子的总磁矩为2.00μB,其中Cr2+对分子磁矩的贡献较大,而配位体上的碳原子和氮原子的贡献相对较小.讨论了当晶格常数发生小幅变化时材料半金属性的变化.  相似文献   

3.
江阔 《中国物理 B》2010,19(4):2801-2807
通过对La0.8Sr0.2Mn1-yCoyO3(y≤02)饱和磁矩和输运的测量,研究了Co对La0.8Sr0.2MnO3的磁电阻影响机制.结果表明,在La0.8Sr0.2Mn1-yCoyO3y≤02)中Co3+离子是低自旋态.由于Mn3+—O—Co3+—O—Mn3+类型的磁交换与Mn3+-Mn4+离子间双交换作用相比较弱,Curie温度TC附近的磁电阻随着Co掺杂量的增加而降低.与此相反,由于Co2+离子与eg巡游电子的反铁磁交换耦合作用,低温区间的磁电阻随着Co掺杂量的增加而升高.  相似文献   

4.
电场作用下高分子中自陷束缚激子的极化   总被引:3,自引:0,他引:3       下载免费PDF全文
用同时计入电场、对称破缺项te和电子-晶格相互作用的紧束缚模型研究了电场作用下高分子中的自陷束缚激子.发现电场使高分子中自陷束缚激子内电荷发生转移,出现极化.极化程度随场强增加,也与te有关.并发现te≤0.1 eV时,双激子态表现出反向极化特性,这一特性可根据极化的量子力学理论得到理解:对高分子的自陷束缚激子,其禁带中央附近存在两个靠得很近的定域电子态即上定域态和下定域态,用微扰论说明了上定域态是反向极化而下定域态为正向极化;双激子态即上  相似文献   

5.
冯宏剑  刘发民 《中国物理 B》2008,17(5):1874-1880
First-principles calculations have been performed to investigate the ground state electronic properties of BaFeO3 (BFO). Local spin density approximation (LSDA) plus U (LSDA+U) treatment modified the metallic behaviour to insulated one with a band gap of 4.12eV. The spontaneous polarization was found to be 89.3\muC/cm2 with Berry phase scheme in terms of the modern theory of polarization. Fe-3d eg were split into two singlet states (dz2 and d x2-y2}), and Fe-3d t2g were split into one doublet states(dxz and dyz) and one singlet states(dxy) after Fe and O displaced along the c axis. Meanwhile the occupation numbers of dz2, dyz, dxz and OT pz (on the top of Fe) were increased at the expense of those in xy plane. Our results showed that it was the sensitivity of hybridization to ferroelectric distortions, not just the total change of hybridization, that produced the possibility of ferroelectricity. Moreover, the increasing occupation numbers of OT pz and Fe dz2 favoured the 180o coupling between Fe-3d eg and Fe-3d t2g, leading to ferromagnetic ordering, which has been confirmed by the increase of magnetic moment by 0.13μB per formula unit in the polarized direction. Hence, the magnetization can be altered by the reversal of external electric field.  相似文献   

6.
张小超  赵丽军  樊彩梅  梁镇海  韩培德 《物理学报》2012,61(7):77101-077101
采用基于密度泛函理论的第一性原理方法对未掺杂以及不同浓度过渡金属Fe,Co,Ni,Zn掺杂金红石TiO2的超晶胞体系进行了几何优化,并讨论了其晶格常数,电子能带结构和光学性质.研究结果表明:掺杂前后的晶格参数与实验值偏差在3.6%以下;适量的过渡金属掺杂不但影响体系能带结构,拓宽光吸收范围,而且扮演着俘获电子的重要角色,有利于光生电子-空穴对的有效分离以及增强光吸收能力;Fe,Co,Ni,Zn最佳理论掺杂体系分别为Ti0.75Fe0.25O2,Ti0.75Co0.25O2,Ti0.75Ni0.25O2,Ti0.83Zn0.17O2;Fe,Co,Ni3d态分裂为t2g和eg态,分别贡献于价带高能级和导带低能级部分,促进了电子-空穴对的生成,从而可提高TiO2的光催化性能;Zn3d态电子成对填满轨道,不易被激发,故光催化活性无明显提高.  相似文献   

7.
采用完全对角化方法,讨论了三角对称和四角对称下d3离子自旋二重态和自旋四重态对基态4A2(4F)自旋哈密顿(SH)参量(包括零场分裂(ZFS)和g因子)的影响机理. 并对影响基态SH参量的四种机理(SO机理,SS机理,SOO机理和SO-SS-SOO联合机理)进行了分析. 结果表明,自旋二重态与四重态对d3离子基态零场分裂都具有重要贡献;而基态g因子主要由四重态决定,二重态对g因子贡献很小. 此外,发现SS机理和SOO机理对基态EPR参量的贡献主要由四重态决定,二重态的影响很小.  相似文献   

8.
魏群  杨子元  王参军  许启明 《物理学报》2007,56(4):2393-2398
提出了解释掺杂离子局域结构畸变的配体平面移动模型,建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上,采用全组态完全对角化方法,对Al2O3晶体中V3+的局域结构和自旋哈密顿参量进行了系统的研究.结果表明,V3+掺入Al2O3晶体后,上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al2O3:V3+晶体的自旋哈密顿参量.在此基础上,研究了三角晶场下3d2离子自旋哈密顿参量的微观起源.研究发现,自旋三重态对自旋哈密顿参量的贡献是主要的,微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关.  相似文献   

9.
通过重离子融合蒸发反应16O(82Se+4n)94Mo布局了94Mo核的高自旋态.利用多探头探测器阵列GASP进行了在束γ测量,从而重新研究了94Mo核的高自旋态能级结构.基于新发现的一些重要的连接跃迁,对94Mo核的高自旋态能级纲图做了重要修改.将新的能级结构与壳模型计算进行了比较和讨论.结果表明要正确的描述94?Mo核的高自旋态(自旋值大于14)能级结构,应考虑价中子在d5/2,g7/2和h11/2轨道上的激发.  相似文献   

10.
本文利用时间切片离子速度成像技术对MgO分子在193 nm下的光解反应动力学进行了研究. 实验通过产物Mg的速度和角度分布分析,发现了三个光解反应路径. 路径一为MgO(X1Σ+)态分子吸收一个光子到MgO(G1π) 态,由于G1π, 33π和15π态之间的自旋轨道耦合作用,反应沿着15π的势能面解离生成产物Mg(3Pu)+O(3Pg). 路径二、三分别为MgO(A1π)态分子吸收一个光子到MgO(G1π)态和MgO(41π) 态,进而解离生成产物Mg(3Pu)+O(3Pg)和Mg(1Sg)+O(1Sg). 光解离路径的各向异性参数与振动能级的寿命以及转动和振动自旋轨道态的耦合有关. 从总动能分析得到D0(Mg-O)=21645±50 cm-1.  相似文献   

11.
吴圣钰  张耘  柏红梅  梁金玲 《物理学报》2018,67(18):184209-184209
利用基于密度泛函的第一性原理的计算方法,研究了Co单掺及Co和Zn共掺LiNbO_3晶体的电子结构和吸收光谱.研究显示,各掺杂体系铌酸锂晶体的带隙均较纯铌酸锂晶体变窄. Co:LiNbO_3晶体禁带宽度为3.32 eV; Co:Zn:LiNbO_3晶体, Zn的浓度低于阈值或达到阈值时,禁带宽度分别为2.87或2.75 eV. Co:LiNbO_3晶体在可见-近红外光波段2.40, 1.58, 1.10 eV处形成吸收峰,这些峰归结于Co 3d分裂轨道的跃迁;加入抗光折变离子Zn~(2+),在1.58, 1.10 eV处的吸收峰增强,可以认为Zn~(2+)与Co~(2+)之间存在电荷转移,使e_g轨道电子减少,但并不影响t_(2g)轨道电子.结果表明,晶体中的Co离子在不同共掺离子下可充当深能级中心(2.40 eV),或可充当浅能级中心(1.58 eV),两种情况下,掺入近阈值的Zn离子均有助于实现优化存储.  相似文献   

12.
The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La0.7Sr0.3MnO3 and La0.5Sr0.5CoO3 has been investigated. It is found that substitution of 10% Ru at the Mn site of La0.7Sr0.3MnO3 decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔTc80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La0.5Sr0.5CoO3. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru+4/Ru+5. The eg and t2g parentage of Ru+5 is similar to Mn+4 and therefore, Ru+5 ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co+3: t2g5eg1), forcing a double exchange FM state to anti-FM state.  相似文献   

13.
Bochao Li 《中国物理 B》2021,30(11):114214-114214
A theory of multiphoton photoemission is derived to explain the experimentally observed monotonic decrease with the wavelength in the electron yield of TiO2 nanoparticles (NPs) by as large as four orders of magnitude. It is found that the fitting parameter corresponds to the energy position of Ti3d eg and t2g states, and the derived theory is a novel diagnostic of excited states in the conduction band, very importantly, applicable to individual NPs. The difference between four-photon slope NPs and three-photon slope NPs is attributed to the difference in defect density. The success of the theory in solving the puzzling result shows that thermal emission from high-lying levels may dominate over direct multiphoton ionization in solids when the photon number larger than four is required.  相似文献   

14.
Gd2Co2Al电子结构和磁性的第一性原理研究   总被引:1,自引:0,他引:1       下载免费PDF全文
张加宏  刘甦  顾芳  杨丽娟  刘楣 《物理学报》2006,55(6):2928-2935
从第一性原理出发,在局域自旋密度近似(LSDA)和LSDA+U(在位库仑能)近似下,采用FPLAPW密度泛函能带计算方法研究了Gd2Co2Al的电子结构和磁性. 从平均场近似出发,估算了体系的居里温度,并分析了导致体系居里温度偏低的原因.研究结果显示Gd2Co2Al为金属导体,其强的铁磁性的提供者主要是Gd,且Co的局域铁磁性是不稳定的. 基于LSDA近似的计算表明Gd2Co2关键词: 稀土过渡族金属间化合物 密度泛函理论 电子结构 磁性性质  相似文献   

15.
The electronic hopping energies and the band structure of a neutral C60 molecule for two kinds of hybridized orbits, sp3 and sp2, are studied using the Wannier function method and tight-binding approximation model, respectively. By comparison, the sp3 hybridized type is superior in the band structure obtained by employing the Wannier function method. When the effective nuclear charge number Z = 1.148 the energy gap (tlu-hu), bandwidth (t3g-ag) and threshold value (t3g-hu) of the ionization energy are 1.70 eV, 11.35 eV and 7.69 eV, respectively. These results are in accord with the experimental values.  相似文献   

16.
Traditional ligand-field theory has to be improved by taking into account both pure electronic contribution and electron-phonon interaction one (including lattice-vibrational relaxation energy). By means of improved ligand-field theory, the R line, t23 2T1 and t23 2T2 lines, t22 (3T1)e4T2, t22 (3T1)e4T1 and t2 e2(4A2)4T1 bands, g factors of t23 4A2 and t23 2E, four strain-induced level-splittings and R-line thermal shift of MgO:V2+ have been calculated. The results are in very good agreement with the experimental data. It is found that for MgO:V2+, the contributions due to electron-phonon interaction (EPI) come from the first-order term; the contributions from the second-order and higher terms are insignificant. In thermal shift of R line of MgO:V2+, the temperature-dependent contribution due to EPI is dominant. The results obtained in this work may be used in theoretical calculations of other effects of EPI.  相似文献   

17.
M. Afshar  M. Hemati 《Physics letters. A》2018,382(48):3476-3482
We have demonstrated electronic configurations and magnetic properties of single Co adatom on benzene (Bz) molecule in the framework of relativistic density functional theory. A sequence of fixed spin moment (FSM) calculations were carried out with and without Coulomb repulsion (U). We have investigated that varying the strength of Coulomb repulsion results to different equilibrium positions for the Co adatom on benzene molecule. It was shown that inclusion of the on-site Coulomb repulsion in the Co 3d orbitals affects significantly the geometry of Co–Bz complex. We also found two stable low-spin and high-spin multiplicities for the complex. The nature of the high-spin configuration was explained according to the Hubbard electron–electron correlation in 3d shell of the Co adatom. Our FSM results indicate that the high-spin state is a global minimum in the presence of Hubbard parameter U. The relativistic spin–orbit coupling and using orbital polarization correction induce considerable orbital magnetism in both low and high spin states of the Co–Bz complex. We have also calculated magnetic anisotropy energies for two spin states and we found out that an out-of-plane magnetic orientation of Co adatom is more favorable in the low spin state whereas the Coulomb repulsion (U = 2 eV and U = 4 eV) predicts an in-plane magnetic orientation for Co adatom. Our findings can be implicitly taken into account for the extended system of added single Co atom on graphene.  相似文献   

18.
李琳  孙宇璇  孙伟峰 《物理学报》2019,68(5):57101-057101
按照基于自旋密度泛函理论的赝势平面波第一原理计算方法,理论研究了两种层堆叠结构氧化钼(正交和单斜MoO_3)的电子结构、磁性和光学特性,探讨其作为电致变色材料或电磁材料在光电子器件中的技术应用.采用先进的半局域GGA-PW91和非局域HSE06交换相关泛函精确计算晶体结构和带隙宽度.计算得出较低密排面解离能,表明两种层状氧化钼的单片层很容易从体材料上剥落.能带结构和投影态密度分析表明:导带底和价带顶电子态主要来自于层平面方向成键的原子轨道,呈现典型的二维电子结构特征.无缺陷的MoO_3块体材料具有明显的磁矩,O空位会导致磁矩增加;由Mo原子和顶点氧原子产生的亚铁磁耦合磁矩是MoO_3层状材料磁性的主要来源;层状氧化钼在可见光区具有明显的光吸收响应,光吸收谱表现出显著的各向异性并在带电时发生明显的蓝移或形成新的低频可见光吸收峰.计算结果证明层状氧化钼具有明显的电致变色和磁控性能,为设计高性能电磁或光电子功能材料提供了理论依据和技术数据.  相似文献   

19.
刘萍  秦真真  乐云亮  左旭 《中国物理 B》2017,26(2):27103-027103
Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz~2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations(GGA) and GGA+U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic(FM) and antiferromagnetic(AFM) states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA+U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.  相似文献   

20.
As a key factor leading to the pressure-dependent R1-line-shift reversal and R1-state lifetime, at 10 K, the pressure-dependent variation of mixing-degree of |t22(3T1)e4T2〉 and |t232 E〉base-wavefunctions in the wavefunction of R1 state of LLGG:Cr3+ has been calculated and analyzed. From this, the physical origin of the pressure-dependent R1-line-shift reversal has been revealed. Furthermore, by using the pressure-dependent values of the sum of all square mixing-coefficients of |t22(3T1)e4T2〉in the wavefunction of R1 state, the lifetimes of R1 state of LLGG:Cr3+ at various pressures have been calculated, which are in good agreement with observed results. The quantum anticrossing effect between t232E and t22(3T1)e4T2 levels due to both spin-orbital interaction and electron-phonon interaction is remarkable, which is related to the admixture of |t22(3T1)e4T2〉and |t232 E〉as well as the low-high crystal-field transition.  相似文献   

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