Al_4团簇在NaCl(001)表面的结构和磁性

利用第一次性原理计算Al4团簇的重心吸附在nACl表面上两种桥位,两种空位,在nA原子顶位及Cl原子顶位的结构、平均每个Al原子的吸附能、最低的Al原子和nACl(001)表面原子之间的距离和磁矩。结果表明,Al4团簇的重心吸附在nACl表面上nA的顶位是最稳定的结构,吸附能最大,总能最大,最低的Al原子和nACl(001)表面原子之间的距离最小,但团簇的磁矩为0μb,其他位置Al4团簇则保留其在自由空间的磁矩

Vibrational modes and lattice distortion of a nitrogen-vacancy center in diamond from first-principles calculations

We investigate vibrational properties and lattice distortion of negatively charged nitrogen-vacancy (NV) center in diamond. Using the first-principles electronic structure calculations, we show that the presence of NV center leads to appearance of a large number of quasilocalized vibrational modes (qLVMs) with different degree of localization. The vibration patterns and the symmetries of the qLVMs are presented and analyzed in detail for both ground and excited orbital states of the NV center. We find that in the high-symmetry ($C_{3v}$) excited orbital state a pair of degenerate qLVMs becomes unstable, and the stable excited state has lower ($C_{1h}$) symmetry. This is a direct indication of the Jahn-Teller effect, and our studies suggest that dynamical Jahn-Teller effect in the weak coupling regime takes place. We have also performed a detailed comparison of our results with the available experimental data on the vibrations involved in optical emission/absorption of the NV centers. We have directly demonstrated that, among other modes, the qLVMs crucially impact the optical properties of the NV centers in diamond, and identified the most important groups of qLVMs. Our results are important for deeper understanding of the optical properties and the orbital relaxation associated with lattice vibrations of the NV centers.Comment: 10 RevTeX pages, 10 EPS figure

锂离子电池正极材料Li2FeO2的电子结构性质和Li扩散

采用基于密度泛函理论的第一性原理方法计算了锂离子电池正极材料Immm-Li2FeO2的声子谱、电子结构性质和Li扩散系数并与Li2MO2 （M=Co, Ni, Cu）材料进行对比.计算结果显示, Immm-Li2FeO2材料具有结构稳定性,计算结果呈铁磁性,能带结构具有半金属的特征. Fe离子外层d电子呈低自旋态,自旋极化P=8.01%.利用分波态密度分析了自旋向上和自旋向下的电子能带结构.此外,采用微动弹性带方法计算了各个方向上Li扩散的势垒,结果表明Li离子比较容易先进行c轴方向的迁移,迁移势垒为0.1 eV;然后再沿ab轴方向迁移,迁移势垒为0.21 eV,而沿a轴方向迁移的势垒为0.39 eV.这些势垒值比其他的Li2MO2 （M=Co, Ni, Cu）材料中的势垒值小,也比其他Fe基Li离子电池正极材料中的势垒值更低,意味着Li2FeO2中的Li离子将有更高的扩散系数,这对Li2FeO2作为正极材料具有重要的意义

锂离子电池正极材料Li2FeO2的电子结构性质和Li扩散

采用基于密度泛函理论的第一性原理方法计算了锂离子电池正极材料Immm-Li2FeO2的声子谱、电子结构性质和Li扩散系数并与Li2MO2(M=Co,Ni,Cu)材料进行对比.计算结果显示,Immm-Li2FeO2材料具有结构稳定性,计算结果呈铁磁性,能带结构具有半金属的特征.Fe离子外层d电子呈低自旋态,自旋极化P=8.01%.利用分波态密度分析了自旋向上和自旋向下的电子能带结构.此外,采用微动弹性带方法计算了各个方向上Li扩散的势垒,结果表明Li离子比较容易先进行c轴方向的迁移,迁移势垒为0.1eV;然后再沿ab轴方向迁移,迁移势垒为0.21eV,而沿a轴方向迁移的势垒为0.39eV.这些势垒值比其他的Li2MO2(M=Co,Ni,Cu)材料中的势垒值小,也比其他Fe基Li离子电池正极材料中的势垒值更低,意味着Li2FeO2中的Li离子将有更高的扩散系数,这对Li2FeO2作为正极材料具有重要的意义

Ordered arrays of identical Nb-4 clusters on the GaN(0001) surface studied with first-principles calculations

Based on the first-principles total-energy calculations within the density-functional theory, the (2 x 2) and (3 x 3) arrays of tetrahedron- and quadrangle-Nb-4 clusters on the GaN(0001) surface have been studied. We show that the periodically two-dimensional arrays of Nb-4 clusters on the GaN(0001) surface are very stable at two of the surface adsorption sites. Once the Nb-4 clusters locate at the stable sites, it is difficult for them to diffuse, since the potential barriers for the diffusions are relatively high. We also predict that on the GaN(0001) surface, the well-ordered (3 x 3) arrays of identical Nb-4 clusters are the ones with maximum density for the tetrahedron- and quadrangle-Nb-4 quantum dots

Interatomic many-body potential model in metal

在本文中,我们构造了金属Ta元素的Finnis-Sinclair型的嵌入原子势。并采用蒙特卡罗方法求解给出了此元素的多体势函数的参数。结果显示,本文拟合的参数能够较好的反映这种元素的结构特征和物理性质。福建省自然科学基金(批准号:Z0513004)资助的课

Atomic and electronic structures of Zr atomic chains

The atomic, binding and electronic structures of very thin Zr chains are studied by the first-principles density-functional method. The present calculations reveal that zirconium can form planar chains in zigzag, dimer and ladder structures. The zigzag geometry has two minima. The most stable geometry is the zigzag one with a unit cell rather close to equilateral triangles with four nearest neighbours. The other stable zigzag structure has a wide bond angle and allows for two nearest neighbours. An intermediary structure has the ladder geometry and is formed by two strands. The dimer structure is also found to be more stable than the truly linear chain. All these planar geometries are more favourable energetically than the linear chain. We also show that by going from Zr bulk to a Zr chain, the characters of bonding do not change significantly

A Two-dimensional Analytical Model to GAT′s Gate Shielding Effect

【中文摘要】 建立了 GAT器件集电结耗尽层电位分布和电场分布的二维解析模型 ,定量研究了GAT的栅屏蔽效应的解析表达式 ,并借助计算机对栅屏蔽效应给以证实。该模型可供优化设计双极型高频、高压、低饱和压降功率器件参考。 【英文摘要】 A two dimensional analytical model of the electric potential and field distribution in GAT’s collector depletion space in the cut off state is derived for the first time.The formula for GAT’s gate shielding effect is derived and the gate shielding effect is proved by aid of computer quantitatively.This model will provide assistance to the optimal design of bipolar power transistor with high frequency and high breakdown voltage.国家自然科学基金( No.69896260 -06); 国家高技术研究发展计划( 863-715-010

An Analysis of GATs Compatibility Between High Current Gain and High Avalanche Breakdown Voltage

【中文摘要】 通过作者最近建立的关于电力半导体器件 GAT的集电结耗尽层电位分析和电场分布的二维解析模型定量研究了 GAT的雪崩击穿特性 ,并且定量解释了该器件实现高击穿电压与高电流增益兼容的实验结果。 【英文摘要】 By the aid of the two dimensional analytical model [5] of the electric potential and field distribution in power semiconductor GATs collector depletion space in a cut off state which was established by the writers lately,the GATs avalanche breakdown characteristics was investigated quantitatively,and the experimental results which concluded that the GATs can realize the compatibility between high breakdown voltage and high current gain,were...国家自然科学基金!( No.69896260-06 );国家高技术研究发展计划( 863-715-010

An Analysis of GATs Compatibility Between High Frequency and High Base Region Punchthrough Voltage

【中文摘要】 通过作者最近建立的关于 GAT器件集电结耗尽层电位分布和电场分布的二维解析模型 ,定量研究了 GAT的基区穿通电压 VPI,并且解释了该器件实现高频率与高电压兼容的实验结果。 【英文摘要】 By the aid of the two dimensional analytical model of the electric potential and field distribution in GATs collector depletion space in a cut off state which was established by the writers lately,the GATs base region punchthrough voltage V PI was investigated quantitatively,and the experimental results which concluded that the GATs can realize the compatibility between high frequency and high voltage were explained.国家自然科学基金( No.69896260-06 );国家高技术研究发展计划( 863-715-010