SiC多型体几何结构与电子结构研究

采用平面波超软赝势法和范数不变赝势法对几种SiC多型体的几何结构、能带结构等进行了系统的研究.结果表明:6HSiC导带最低点在ML线上U点,用平面波超软赝势法计算时U点在(0000,0500,0176)点附近;而用范数不变赝势法计算时在导带最低点附近能带呈现不连续点,不连续点出现在(0000,0500,0178)点附近.两种赝势法计算结果相比,用平面波超软赝势法得到的导带最低点位置更靠近布里渊区M(0,05,0)点.在平面波超软赝势下,随着六角度的增加,cp,cpa增大的趋势较为明显,能隙和价带宽度变宽的趋势也较为明显.在计算极限内,绝对零度下4HSiC系统能量最低、最稳定,而Ewald能量显示3CSiC最稳定. 关键词： 密度泛函理论 电子结构 SiC     

掺入Ni2+和V3+对α-Al2O3晶体光谱精细结构、晶体局域结构和零场分裂参量的影响

应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了V³⁺∶α-Al₂O₃和Ni²⁺∶α-Al₂O₃晶体的光谱精细结构、晶体局域结构和零场分裂参量,研究了掺入两种互补态离子Ni²⁺和V³⁺对同种晶体的光谱精细结构、晶体局域结构和零场分裂参量的影响,理论计算值和实验值相符.研究发现：掺杂没有改变晶体的光谱精细结构和能级分裂条数,但改变了能级间距|掺杂也没有改变晶体的对称性,但使晶体局域结构发生了一定程度的畸变| Ni²⁺∶α-Al₂O₃晶体局域结构的伸长畸变量大于V³⁺∶α-Al₂O₃晶体,键角的变化量小于V³⁺∶α-Al₂O₃晶体.     

(BCO)12与(CH)12稳定性的环张力分析

基于密度泛函理论的B3LYP方法, 对具有等瓣相似性的(BCO)12和(CH)12的10种异构体结构的稳定性进行了计算对比研究, 这10种异构体由三元、四元、五元和六元环组成. 环张力分析表明对羰基硼笼体系, 三元环起主要的稳定化作用, 而四元环是张力的主要来源, 对碳氢笼体系, 五元环起主要的稳定化作用. 电子差分密度表明羰基硼笼中的三元环与碳氢笼中的三元环有不同的电子结构, 导致了它们不同的张力表现. 核独立化学位移(NICS)分析表明, 尽管σ芳香性不是稳定性的决定因素, 但对笼的稳定性有一定的影响.     

Monocyclic boron carbonyls: novel aromatic compounds

Monocyclic boron carbonyls, (BCO)nm, with 4n + 2 delocalized electrons are highly aromatic, as indicated by the computed nucleus independent chemical shift (NICS) and the computed energies for benzene analogue.     

Texture development and magnetic properties of [ZrO2/CoPt]n/Ag nanocomposite films

The L1₀ CoPt films with (0 0 1) preferred orientation are achieved by fabricating on the glass substrates and post annealing at 600° C for 30 min. The preferred orientation of [ZrO₂/CoPt]_n/Ag films dependence of the Ag underlayer thickness, ZrO₂ and CoPt interlayer thickness is investigated. A large perpendicular magnetic anisotropy and a nearly perfect L1₀ CoPt (0 0 1) texture are obtained in the [ZrO₂ (3 nm)/CoPt (5 nm)]₃/Ag (10 nm) film. The existence of ZrO₂ plays an important role in reducing the intergranular interactions and in determining the size of CoPt grains. Magnetic reversal in textured CoPt films are close to a Stoner-Wolfarth rotation.     

(HBNH)n团簇的结构和稳定性

Structures and thermodynamic properties of the imidoboranes （HBNH）n （n=1-16） have been investigated theoretically at the B3LYP/6-31G^＊ level of theory. Needle-shaped oligomers that violate the isolated square rule were found to be more stable than cage isomers. The needle-shaped oligomer with n=16 was predicted to be exceptionally stable at low temperature, hexamer and octamer clusters dominated the gas phase at higher temperature. The highest oligomerization degree of the spontaneous cluster fomation has been estimated. It was concluded that generation of the gas phase （HBNH）n clusters with oligomerization degree n ≥24 was viable, making these species possible intermediates involved in the gas phase generation of BN nanoparticles.     

BN纳米管内含C纳米管——结构与电学性质

运用密度泛函理论的PW91/DNP方法对C(6,0)@BN(n,0)体系的结构与稳定性进行了研究, 发现最适合与C(6,0)纳米管形成的嵌套体系的锯齿型BN纳米管是BN(15,0)和BN(16,0), 在形成的C(6,0)@BN(15,0) 和 C(6,0)@BN(16,0)中, 碳壁与氮化硼壁之间的距离分别为0.36和0.40 nm. 在最稳定的C(6,0)@BN(16,0)体系中, 发现内层碳纳米管的电子结构并未受到外层氮化硼纳米管的影响, 然而氮化硼纳米管的能隙缩小了0.5 eV. 对C(6,0)@BN(16,0)的轨道分析表明, 碳纳米管与氮化硼纳米管之间的作用力为范德华力.     

AlmN2 (m=1～8)团簇结构与稳定性的DFT研究

用密度泛函理论(DFT)的B3LYP方法，在6-31G*水平上对AlmN2(m=1～8) 团簇的几何构型、电子结构、振动频率和热力学性质进行了理论研究. 结果表明， AlmN2团簇的基态结构有两种基本构型， m≤2的结构是以N－N键为核心周围与Al原子相配位形成的; m >2的结构是由两个AlnN（n< m）分子碎片通过共用Al原子或Al－Al键相互结合形成的，这为较快找到AlmN2团簇基态结构提供了一条有效途径. 通过对基态结构能量二次差分的讨论，得到了m为偶数的AlmN2团簇比m为奇数的稳定.     

GaxPy(x+y=8)及其阴离子团簇的结构与性质的DFT研究

用密度泛函理论方法对半导体二元微团簇GaxPy和GaxPy−(x+y=8)的几何结构、电子态、能量等进行了计算, 在B3LYP/6-311+G(2df)水平下完成结构优化和频率分析. 讨论了电荷诱导结构发生变化情况, 与中性团簇相比, 在阴离子团簇中, Ga—P键较P—P键有利于形成. 预测了未知Ga1P7−、Ga2P6−、Ga3P5−、Ga6P2−和Ga7P1−化合物的最稳定结构存在的可能性, 得出在GaxPy和GaxPy−(x+y=8)中, Ga4P4和Ga4P4−比较稳定. 给出了两种能差即绝热电子亲合势(ΔEAEA)和垂直电离能(ΔEVDE), 并与相关文献作比较. Ga4P4和Ga5P3的绝热电子亲合势与实验值相当吻合. 布居分析表明, 磷化镓团簇的成键属于混合键型.     

Cu6S4 cluster based twelve-connected face-centered cubic and Cu19I4S12 cluster based fourteen-connected body-centered cubic topological coordination polymers

Hydrothermal reaction of Cu(MeCO2)2, (4-pyridylthio)acetic acid and NH4SCN resulted in a twelve-connected face-centered cubic topological metal-organic framework [Cu3(pdt)2(CN)] (pdt = pyridinethiolate) in which Cu6S4 clusters act as twelve-connected nodes and pyridine rings and cyanides act as connectors. As an extension, an unprecedented fourteen-connected body-centered cubic coordination polymer [Cu19I4(pdt)12(SH)3] has been synthesized by three methods, in which nanosized chiral Cu19I4S12 clusters act as fourteen-connected nodes and triple pyridine rings and hydrosulfides act as connectors. The in situ S-C(sp(3)), S-C(sp(2)), and S-C(sp) cleavage reactions have been observed in the work.