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1.
采用密度泛函理论中广义梯度近似对非典型富勒烯C 22和过渡金属内掺衍生物 M@C 22( M=Sc,Ti,V,Cr,Mn,Fe,Co和Ni)的几何结构和电子结构进行计算研究.发现非典型富勒烯C 22的基态结构是含有一个四碳环的单重态笼状结构.过渡金属原子的掺入明显提高了体系的稳定性. C-M键既有一定共价性又有一定离子性.磁性、能级图、轨道分布和态密度图分析表明: M原子的3d轨道和碳笼的C原子的原子轨道之间存在较强的轨道杂化. Ti, Cr, Fe和Ni内掺的结构出现磁性完全猝灭现象. Sc和碳笼间是弱反铁磁作用, V,Mn和Co与碳笼间是弱铁磁作用. 相似文献
2.
采用基于密度泛函理论的第一性原理方法, 在广义梯度近似(GGA)和GGA+ U方法下对尖晶石型LiMn 2O 4及其Al掺杂 的尖晶石型LiAl 0.125Mn 1.875O 4晶体的结构和电子性质进行了计算. 结果表明: 采用GGA方法得到尖晶石型LiMn 2O 4是立方晶系结构, 其中的Mn离子为+3.5价, 无法解释它的Jahn-Teller 畸变. 给出的LiMn 2O 4能带结构特征也与实验结果不符. 而采用GGA+ U方法得到在低温下的LiMn 2O 4和其掺杂 体系LiAl 0.125Mn 1.875O 4的晶体都是正交结构, 与实验一致. 也能明确地确定Mn的两种价态Mn 3+/Mn 4+的分布并且能够说明Mn 3+O 6的 z方向有明显的Jahn-Teller 畸变, 而Mn 4+O 6则没有畸变. LiMn 2O 4的能带结构与实验比较也能够符合. 采用GGA+U方法对Al掺杂体系的LiAl 0.125Mn 1.875O 4的研究表明, 用Al替换一个Mn不会明显地改变晶体的电子性质, 但可以有效地消除Al 3+O 6 八面体的Jahn-Teller畸变, 从而改善正极材料LiMn 2O 4的性能, 这与电化学实验的观察结果相一致. 相似文献
3.
利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种 S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫 α的增强将从磁有序相变化到自旋无序相,并且伴随着自旋能隙的出现,量子相变点为 α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着 α的增强而减弱,阻挫在0≤ α< 相似文献
4.
用水热技术合成了单相正交LiMnO 2( o-LiMnO 2)粉末,X射线衍射表明其空间群为 Pmnm.X射线衍射精修结果指出该材料存在少量的阳离子无序,但这种无序对材料的磁性没有表现出明显的影响.静态和动态的磁性研究结果表明 o-LiMnO 2中存在重入自旋玻璃行为,即在 T≤ TC≈118K,反铁磁态转向铁磁态,在 T≤ Tf≈50K,铁磁态又转向自旋倾斜玻璃态. 相似文献
5.
对Eu 1-xSr xMnO 3 ( x=0.4, 0.5, 0.6, 0.7) 体系的磁结构进行了系统的研究. 通过核磁共振实验, 磁化测量, 并结合电输运测量结果表明, Sr的掺入使得 EuMnO 3反铁磁母相中出现铁磁相. 铁磁相和反铁磁相的竞争导致样品在低温下的自旋玻璃行为.分析认为, Eu 0.4Sr 0.6MnO 3和Eu 0.3Sr 0.7MnO 3的磁结构在低温下呈现更加复杂的特征, 主要源于铁磁团簇的形成以及无序相的存在. 相似文献
6.
基于自旋-轨道-晶格Hamilton量,应用团簇自洽场方法,研究了双层钙钛矿结构材料K 3Cu 2F 7基态的晶格、磁及轨道结构,发现近孤立的双层的对称破缺和Jahn-Teller晶格畸变使得Cu 2+离子在每层内交替占据 z 2-x 2〉/ z 2-y 2〉轨道,进而导致双层的层间表现为强的反铁磁耦合,层内为弱的铁磁耦合.强反铁磁耦合导致层间 相似文献
7.
通过固相反应烧结法成功制备了层状钙钛矿La 1.3Sr 1.7Mn 2-xCu xO 7多晶,主要研究了其磁电特性.结果表明,样品为Sr 3Ti 2O 7型钙钛矿结构.随着温度的降低,其磁性经历了一个很复杂的转变过程.当 x=0时,在 T*=231K出现二维短程铁磁有序,在< 相似文献
8.
基于相对论扭曲波理论方法,并利用新发展的处理极化电子碰撞激发的计算程序REIE06, 系统计算了中性镁原子基态3s 2 1S0到激发态3s3p 1P1, 3s4p 1P1的电子碰撞激发微分截面和角关联(Stokes)参数,计算过程中系统地考虑了相对论效应、电子关联效应等. 部分计算结果与已有的实验和理论结果进行了比较,得到了较好的一致性. 相似文献
9.
应用群论及原子分子反应静力学方法推导了SiO 2分子的电子态及其离解极限,采用B3P86方法,在6-311G **水平上,优化出SiO 2基态分子稳定构型为单重态的 C2V构型,其平衡核间距 Re= RSi—O=0.1587 nm,∠OSiO=111.2°,能量为-440.4392 a.u..同时计算出基态的简正振动频率:对称伸缩振动频率 ν(B 2)=945.4cm -1,弯曲振动频率 ν(A 1)=273.5 cm -1和反对称伸缩振动频率 ν(A 1)=1362.9cm -1.在此基础上,使用多体项展式理论方法,导出了基态SiO 2分子的全空间解析势能函数,该势能函数准确再现了SiO 2( C2V)平衡结构. 相似文献
10.
利用不变本征算符法, 计算低温下自旋为1/2的 XY模型一维亚铁磁棱型链系统的元激发谱, 讨论在此系统中不同的特殊情形下的元激发能量, 从而给出体系的三个临界磁场强度的解析解 HC1, HC2, Hpeak. 分析不同外磁场下 体系的磁化强度随温度的变化规律, 发现三个临界磁场强度的解析解 HC1, HC2, Hpeak是正确的, 并从三个元激发对磁化强度的贡献进行了说明. 低温下磁化强度随外磁场的变化呈现1/3磁化平台. 体系的磁化率随温度或者外磁场的变化都出现了双峰现象. 这说明双峰源于二聚体分子内电子自旋平行排列的铁磁交换作 用能和二聚体与单基体分子间电子自旋反平行排列的反铁磁交换作用能, 热无序能, 外磁场强度相关的自旋磁矩势能之间的竞争. 相似文献
11.
采用基于密度泛函理论的投影平面波方法,对后钙钛矿结构( Ppv)的CaRhO 3的电子结构和磁学性质进行了研究.广义梯度(GGA)近似下的计算表明, Ppv-CaRhO 3的基态为铁磁性半金属,Rh 4+离子的磁矩大小为0.57 μB,具有低自旋态构型;而考虑在位库仑作用修正的GGA+ U计算,得到了与实验结果相符的反铁磁绝缘体基态,表明后钙钛矿结构中4d电子之间的关联效应对体
关键词:
电子结构
磁学性质
金属绝缘体转变 相似文献
12.
ABSTRACT Based on the full-potential linearised augmented plane wave plus local orbitals (FP-L/APW?+?lo) method within the density functional theory (DFT), the structural, electronic, and magnetic calculations of the cubic oxide perovskite NdInO 3 compound have been done under the generalised gradient approximation (GGA). The exchange and correlation (XC) potential is defined as GGA framework in the analyses of structural properties, while both GGA and GGA?+? U ( U is the Hubbard correlation term) approximations are taken to treat the electronic and magnetic properties. It is found that ferromagnetic (FM) configuration is reported as the most stable ground state of the cubic NdInO 3 material; however, the equilibrium lattice parameters such as lattice constant ( a0 ), bulk modulus ( B0 ), its first-pressure derivative ( B’), and the minimum of total energy ( E0 ) are given in paramagnetic (PM), ferromagnetic (FM), and anti-ferromagnetic (AFM) states. The spin-polarized electronic structure calculations (band structure and density of states) of the cubic oxide perovskite NdInO 3 compound verify the half-metallic feature due to the spin-up case which has the metallic nature, whereas the spin-down case presents the semiconducting character. Moreover, the magnetic properties show the integer value of the total magnetic moment for the studied compound ( 3μB ), where it is manly contributed by Nd atoms with apparition of weak local magnetic moments in non magnetic In and O sites. 相似文献
13.
The total energies and electronic structures of SrMnO 3 are studied from first principles calculations within the generalized-gradient approximation (GGA) framework. The orthorhombic structure with AFM1 configuration (see Fig. 1) is found to be the ground state of SrMnO 3, consistent with the latest experimental observation. The orthorhombic distortion effect of SrMnO 3 is studied by comparing its electronic structure and that of cubic structure, while correlation effect is evaluated by comparing GGA and GGA+ U calculations. In contrast to previous theoretical studies, our calculations show that both the orthorhombic distortion and the electron correlation play important roles in the electronic structure of SrMnO 3. 相似文献
14.
The electronic structure and ferromagnetic stability of Co-doped SnO 2 are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+ U schemes. The addition of effective UCo transforms the ground state of Co-doped SnO 2 to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+ UCo calculations show that the pure substitutional Co defects in SnO 2 cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+ UCo show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of UCo enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb UO on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+ UCo calculations are not changed by the correction of band gap. 相似文献
15.
First-principles calculations are performed to study the electronic structures and magnetic properties of C-doped AlN. Both generalized gradient approximation (GGA) and GGA+ U calculations show that a substitutional C atom introduces magnetic moment of about 1.0 μB, which comes from the partially occupied 2p orbitals of the C, its first neighboring Al and first neighboring N atoms (GGA) or out-of-plane first and fifth neighboring N atoms (GGA+ U), among which the atomic moment of the C is the biggest. The U correction for the anion-2p states obviously changes the magnetic moment distribution of Al and N atoms and transforms the ground state of C-doped AlN to insulating from half-metallic. The C atoms can induce ferromagnetic ground state with long-range couplings between the moments in C-doped AlN. The ferromagnetic coupling can be explained in terms of the two band coupling model. 相似文献
16.
ABSTRACTThe spin-polarized structural, electronic and magnetic properties of the Ti-doped zincblende ZnS compound at x?=?0.50 (Zn 0.50Ti 0.50S alloy) have been investigated by employing the first-principles full-potential linearised augmented plane wave with local orbitals (FP-L/APW?+?lo) method within the frame-work of spin-polarized density functional theory (spin-DFT). For the treating of the structural properties, the electronic exchange and correlation (XC) functional was defined by generalised gradient approximation (GGA), whereas both GGA and GGA?+? U approximations are applied to treat and to compare the electronic and magnetic properties ( U is the Coulomb repulsion energy). It has been confirmed that the ferromagnetic (FM) state of this alloy is found the most stable phase; however, all the equilibrium lattice parameters such as; lattice constant ( a0), bulk modulus ( B0), and its first-pressure derivative ( B′) are computed in all paramagnetic, ferromagnetic and anti-ferromagnetic phases. The calculations of electronic properties unveil the perfect half-metallic character in the tetragonal Zn 0.50Ti 0.50S system. The computed magnetic properties reveal that the total magnetic moment is mainly originated from the transition element (TM) of Ti. Moreover, we have found that the p-d hybridisation is the paramount responsible for the reduction of the magnetic moment of TM from its free space charge value and for the production of minor magnetic moments on the nonmagnetic Zn and S sites. 相似文献
17.
The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiCO3 strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C-C dimer pair accompanied by stronger C-C and weaker C-Ti hybridizations as the C-C distance becomes smaller. As the C-C distance increases, C-doped SrTiCO3 changes from an n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates the possibility of tailoring the magnetic and electronic properties of C-doped SrTiO3, which might provide some guidance to extend the applications of strontium titanate as a magnetic or optoelectronic material. 相似文献
18.
基于密度泛函理论的广义梯度近似(GGA)和投影缀加波(PAW)方法,分别从共线和非共线磁性结构出发,研究了自旋阻挫三角反铁磁AgCrO 2的基态、磁性以及电子结构,从理论计算的角度给出了基态磁性结构.计算结果表明:AgCrO 2具有120°螺旋自旋序反铁磁基态,其自旋螺旋面平行于(110)面或(11 -0)面;由于Cr离子间的自旋几何阻挫,导致沿晶体的 a, b和 a+b方向上均形成了螺旋自旋转动角为120°的
关键词:
第一性原理
交换相互作用
阻挫
反铁磁 相似文献
19.
First principles studies based on density functional theory (DFT) calculations within the generalized gradient approximations (GGA) and GGA + U approach using the full-potential, augmented plane wave + local orbitals (APW + lo) method, as implemented in the WIEN2k code, have been used to investigate the structural, electronic and magnetic properties of spinel-structure LiV 2O 4, in particular regarding the heavy fermion (HF) behaviour. The calculations were performed for ferromagnetic, anti-ferromagnetic, and ferrimagnetic configurations using two kinds of magnetic structures (tetragonal and rhombohedral). The GGA results showed that the Fermi energy lies in the V 3d (t 2g) bands with 1.5 electrons per V atom occupying this band, and the V 3d bands are separated by a ~1.9 eV energy gap from the O 2p bands and further split into t 2g and e g bands with a ~1.0 eV energy gap, which are in good agreement with the photoelectron spectra. The GGA + U method indicates that the ground state of LiV 2O 4 is the tetragonal anti-ferromagnetic configuration with metallic character, and ferromagnetic order character at slightly higher energy, which is consistent with experimental result. The geometric frustration and hybridization between 3d (V) and 2p (O) could induce spin fluctuation and help to explain the instability of specific heat, susceptibility and HF behaviour. 相似文献
20.
Generalized gradient approximation (GGA) and GGA + U ( U denotes on-site Coulomb interactions) methods are applied to investigate the magnetic and electronic structures of the perovskite oxide Nd 2/3Sr 1/3MnO 3. Under GGA the compound prefers ferrimagnetic ordering in which Nd sublattice is spin-antiparallel to Mn sublattice. Nd 4f states cross over the Fermi level under GGA, leading the ferrimagnetic Nd 2/3Sr 1/3MnO 3 to a metallic character. The on-site Coulomb interactions should be included to emphasize the localized feature of Nd 4f states. Under GGA + U, the spins of Nd and Mn sublattices tend to be parallel in the ground state, and fully spin-polarized Mn 3d electrons yield a half-metallic band structure for the ferromagnetic Nd 2/3Sr 1/3MnO 3. The ferromagnetic coupling between Nd and Mn sublattices is ascribed to the super-exchange interaction between Nd 4f and Mn 3d ( t2g) electrons via O 2p electrons. 相似文献
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