2'-脱氧鸟苷在水溶液中激发态氢键动力学的密度泛函理论研究

用密度泛函理论和含时密度泛函理论研究了2'-脱氧鸟苷在水溶液中形成的一水和二水复合物在基态和激发态的氢键性质．计算了两种复合物的稳定构型、红外光谱、前沿分子轨道以及密里根电荷等光物理参数．结果表明,两种水合物的分子内氢键在光激发下变化不一致,分子间氢键变化相似．一水复合物的分子内氢键N3···H4-O2 在激发态是加强的,二水复合物的是减弱的．两种水合物的分子间氢键N2-H2···O3和O3-H5···O2及O3···H7-O4和H5···O1-C1在激发态全是减弱的．两种复合物红外光谱的计算结果与实验值一致．二水复合物中分子间氢键O4···H1-N1在激发态断裂,形成了新的分子间氢键O4···H3-N2,这种变化可能与鸟嘌呤部分的结构弯曲有关．最后分析了一水和二水复合物分子的分子内电子转移特性．     

腺嘌呤-水分子团簇的理论研究

利用密度泛函理论在B3LYP/6-311++G(d , p)基组水平上对C5H5N5·(H2O)m (m=1~3)进行了优化与振动频率计算,得到了团簇的六种稳定结构. 应用AIM程序计算了三种最稳定结构的氢键临界点的拓扑参数,结果表明,O—H…N氢键的形成使得O—H之间电子密度减小,伸缩振动频率减小,产生了红移;N—H…O氢键的形成使得N—H之间的电子密度减小,键的强度变弱,伸缩振动频率变小,发生了红移. 利用veda4软件对团簇C5H5N5·(H2O)m (m=0~3)的红外光谱的振动频率进行模式指认,并对部分振动频率进行了比较.     

水分子在不同电荷态的重离子作用下的离化作用

运用含时密度泛函理论和局域密度近似方法,计算了水分子H2O在速度为12.5 a0/fs的重离子C+和C2+作用下产生的各种电荷态的水分子离子的几率,平均逃逸电子数和偶极矩的变化随时间的演化.计算结果表明,在重离子势最大时,电偶极矩的变化最大;重离子远离分子时,重离子的电荷态越高,产生高电荷态分子的几率反而越小.     

芳香性取代基对2-(2-羟基苯基)苯并咪唑激发态质子转移和光谱性质影响的理论研究

运用密度泛函(DFT)和含时密度泛函(TD DFT)理论方法研究了在2-(2-羟基苯基)苯并咪唑(HBI)苯环羟基的对位分别被呋喃基、吡咯基等五种芳香性取代基后的衍生物(HBI-R)分子内质子转移过程,考察了取代基的电子离域效应对分子结构、分子内氢键和质子转移的影响,模拟计算了各分子的IR振动光谱和电子光谱。研究发现,基态的HBI与HBI-R分子内氢键O—H…N比O…H—N强度大,因氢键中的O—H增长和H—N的缩短,激发态氢键O—H…N弱于O…H—N强度,基态和激发态的稳定构型分别为醇式和酮式结构,取代基总体上使酮式构型相对稳定性有所增加,但呋喃基、吡咯基和噻吩基却略降低了激发态酮式构型相对稳定性。取代基降低了HBI基态和激发态分子内质子转移反应的能垒,但影响不大。电子吸收光谱的最大吸收峰和荧光光谱的最大发射峰主要源于前线分子轨道HOMO与LUMO之间的电子跃迁,芳环取代基增强了电子离域效应,使光谱的吸收峰和发射峰波长均有较大的红移。     

Ne-CH4分子间相互作用势的局域密度近似计算

利用基于密度泛函理论框架下的局域密度近似方法对Ne-CH4分子间的相互作用势进行了计算. 发现 当Ne原子和CH4分子之间的距离约为5.8 a.u.时, 计算的势能曲线存在最小值, 对应的势阱深度约为0.053 eV. 计算结果与实验值符合较好.     

Ne-CH4分子间相互作用势的局域密度近似计算

利用基于密度泛函理论框架下的局域密度近似方法对Ne-CH4分子间的相互作用势进行了计算. 发现: 当Ne原子和CH4分子之间的距离约为5.8 a.u.时, 计算的势能曲线存在最小值, 对应的势阱深度约为0.053 eV. 计算结果与实验值符合较好.     

乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)的稳定结构特性研究

采用密度泛函理论M06-2X方法, 在6-311 ++G(2d,2p)// 6-311 ++G(d,p)基组水平上对乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)进行计算, 得到乙醇-水分子团簇的各种稳定构型, 并对乙醇水分子团簇的结构特点进行了分析, 优化的各种低能结构、结构参数、氢键、结合能、平均氢键参数、NBO电荷分布等．结果表明: 最低能稳定结构都是环状的, 而且这些团簇除了形成O―H…O型主氢键外, 还有另一种作用方式C―H…O, 称之为次氢键．虽然C―H…O氢键远弱于O―H…O氢键, 但是对团簇的某些性质也有一定的影响.     

乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)的稳定结构特性研究

采用密度泛函理论M06-2X方法, 在6-311 ++G(2d,2p)// 6-311 ++G(d,p)基组水平上对乙醇-水分子团簇(C2H5OH)nH2O(n=1-4)进行计算, 得到乙醇-水分子团簇的各种稳定构型, 并对乙醇水分子团簇的结构特点进行了分析, 优化的各种低能结构、结构参数、氢键、结合能、平均氢键参数、NBO电荷分布等．结果表明: 最低能稳定结构都是环状的, 而且这些团簇除了形成O―H…O型主氢键外, 还有另一种作用方式C―H…O, 称之为次氢键．虽然C―H…O氢键远弱于O―H…O氢键, 但是对团簇的某些性质也有一定的影响.     

理论研究C8H80-（H2O）n（n=1～5）团簇

应用密度泛函B3LYP／6—31＋G（d，p）方法对C8H80-（H2O）n（n=1～5）团簇这种弱相互作用体系进行垒自由度能量梯度优化，得到该系列团簇的稳定蛄构．计算结果表明。在该系列二元团簇中，一方面水分子数目的多少对苯基丙酮分子的结构影响很小，另一方面由于苯基丙酮分子的存在，破坏了团簇中水分子的对称性结构，在团簇内部极力形成O—H—O这样弯曲的有方向性的氢键．对苯基丙酮-水这样结构复杂的团簇，指认光谱的难度非常大，本文只讨论了与C=O有关的振动峰和水分子的对称伸缩振动的最强峰．     

1,1,3,3-四甲基脲—溶剂氢键复合物的理论研究

采用密度泛函理论在B3LYP/6-311++G(d,p)水平上对水、苯胺、氯仿与1,1,3,3-四甲基脲分子形成的1:1气相氢键复合物进行计算研究.结果表明,三种物质与1,1,3,3-四甲基脲形成的复合物存在氢键,表现为羰基氧原子的孤对电子与H—X(X=O,N,C)反键轨道的相互作用.氢键的形成使C=O和H—X的伸缩振动频率红移.在标准压力和298.15 K下,氢键复合物的形成是一个放热的非自发过程.     

Augmented Kierlik--Rosinberg Fundamental Measure Functional and Extension of Fundamental Measure Functional to Inhomogeneous Non-hard Sphere Fluids

From point of view of weighted density procedure, it is guessed that a Percus-Yevick （PY） compressibility excess free energy density, appearing in the Kierlik Rosinberg type fundamental measure functional （KR-FMF） and expressed in terms of scaled particle variables, can be substituted by a corresponding expression dictated by a more accurate Mansoori Carnahan-Starling Leland （MCSL） equation of state, while retaining the original weighting functions; it is numerically indicated that the resultant undesirable non-self-consistency between the PY type weighting function and MCSL type excess free energy density had no bad effect on the performance of the resultant augmented KR-ffMF which, on the one hand, preserves the exact low-density limit of the original KR-FMF and holds a high degree of pressure self-consistency, on the other hand, improves significantly, as expected, the predictions of density profile of hard sphere fluid at single hard wall contact location and its vicinity, and of the bulk hard sphere second order direct correlation function （DCF）, obtained from functional differentiation. The FMF is made applicable to inhomogeneous non-hard sphere fluids by supplementing a functional perturbation expansion approximation truncated at the lowest order with summation of higher order terms beyond the lowest term calculated by the FMF for an effective hard sphere fluid; the resultant extended FMF only needs second order DCF and pressure of the fluid considered at coexistence state as inputs, consequently is applicable whether the considered temperature is above critical point or below critical point. The extended MCSL-augmented KR-FMF is found to be endowed with an excellent performance for predictions of density profile and surface tension by comparing the present predictions of these two quantities with available computer simulation data for inhomogeneous hard core attractive Yukawa fluid and Lennard-3ones fluid.     

Localization of π‐electron density in twisted bilayer graphene

In bilayer graphene, mutual rotation of layers has strong effect on the electronic structure. We theoretically study the distribution of electron density in twisted bilayer graphene with the rotation angle of 21.8° and find that regions with AA‐like and AB‐like stacking patterns separately contribute to the interlayer low‐energy van Hove singularities. In order to investigate the peculiarities of interlayer coupling, the charge density map between the layers is examined. The presented results reveal localization of π‐electrons between carbon atoms belonging to different graphene layers when they have AA‐like stacking environment, while the interlayer coupling is stronger within AB‐stacked regions.

Charge density map for bilayer graphene with a layer twist of 21.8° (interlayer region).     

Electronic structure of twinned ZnS nanowire

The electronic properties of twinned ZnS nanowires （NWs） with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal （2H） stacking inside the cubic （3C） stacking has no effect on the electronic properties of thin ZnS NWs.     

Superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5

Recently, the discovery of vanadium-based kagome metal AV₃Sb₅ (A= K, Rb, Cs) has attracted great interest in the field of superconductivity due to the coexistence of superconductivity, non-trivial surface state and multiple density waves. In this topical review, we present recent works of superconductivity and unconventional density waves in vanadium-based kagome materials AV₃Sb₅. We start with the unconventional charge density waves, which are thought to correlate to the time-reversal symmetry-breaking orders and the unconventional anomalous Hall effects in AV₃Sb₅. Then we discuss the superconductivity and the topological band structure. Next, we review the competition between the superconductivity and charge density waves under different conditions of pressure, chemical doping, thickness, and strains. Finally, the experimental evidence of pseudogap pair density wave is discussed.     

高压下Zn2GeO4带隙变化的第一性原理研究

采用基于密度泛函理论的第一性原理计算研究了Zn₂GeO₄晶体在高压下的电子结构和带隙变化行为. 研究结果发现, 随着压强的增加, Zn₂GeO₄ 能带间隙先变大, 在压强为9.7 GPa时达到最大值, 然后减小. 通过电子态密度、电荷布居数和电子差分密度分布图的研究分析可知:在低压区域(0< P< 9.7 GPa), 带隙的变大主要是由于原子间距离的减小造成的共价性增强和Ge原子随压强的变大局域性增强引起的; 在高压区域(P>9.7 GPa), 则是出现了离域现象, 诱发了离域电子的产生, 从而使带隙减小.     

非传统超导PuCoGa5晶体结构和电子性质的密度泛函理论研究

基于密度泛函理论的全势能线性缀加平面波方法（FLAPW）,采用局域自旋密度近似（LSDA）及LSDA+U方法报道了Pu基超导体系PuCoGa₅的晶格参数,原子占位和电子性质.LSDA+U方法不仅考虑Pu-5f而且考虑了Co-3d的库伦排斥作用U和Hund交换相关作用J.结果表明LSDA+U在同时考虑Pu和Co的强关联作用时晶格参数和原子占位与相关理论和实验数据吻合较好,特别是PuCoGa₅中Pu-5f的强定域特征尤其是自旋向下的电子.此外,Pu-5f与Co-3d电子的轨道杂化明显强于Ga-4p电子.     

Theoretical studies on 2‐(5‐amino‐3‐nitro‐1,2,4‐triazolyl)‐3,5‐dinitropyridine (PRAN) and its derivatives

In this work, a set of derivatives of 2‐(5‐amino‐3‐nitro‐1,2,4‐triazolyl)‐3,5‐dinitropyridine (PRAN) with different energetic substituents (?N₃, –NO₂, –NH₂, –NF₂) have been studied at the Becke, three‐parameter, Lee–Yang–Parr/aug‐cc‐pvdz, Becke, three‐parameter, Lee–Yang–Parr/6‐31G(d), Becke, three‐parameter, Perdew 86/6‐31G(d), and Becke three‐parameter, Perdew–Wang 91/6‐31G(d,p) levels of density functional theory. The gas‐phase heats of formation were predicted with isodesmic reactions and the condensed‐phase HOFs were estimated with the Politzer approach. The effects of different functionals and basis sets were analyzed. –N₃ and –NO₂ greatly increase while –NH₂ and –NF₂ slightly decrease heats of formation. An analysis of the bond dissociation energies and impact sensitivity shows that all compounds have good stability. The crystal densities (1.82–2.00 g/cm³) computed from molecular packing calculations are big for all compounds and that of the –NF₂ derivative is the largest. All derivatives have higher detonation velocity and detonation pressure than PRAN. Compounds 3 and 4 (R = NO₂ and NF₂) have better performance than hexahydro‐1,3,5‐trinitro‐1,3,5‐trizine and the performance of 4 is quite close to that of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane, they are promising candidates of high energy compounds and worth further investigations. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural,electronic and magnetic properties of the Mn-Ni(110) c(2×2) surface alloy

<正>Using first-principles total energy method,we study the structural,the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy.Paramagnetic,ferromagnetic,and antiferromagnetic surfaces in the top layer and the second layer are considered.It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases.The buckling of the Mn-Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26 A(1 A=0.1 nm) and the weak rippling is 0.038 A in the third layer,in excellent agreement with experimental results.It is proved that the magnetism of Mn can stabilize this surface alloy.Electronic structures show a large magnetic splitting for the Mn atom,which is slightly higher than that of Mn-Ni(100) c(2×2) surface alloy(3.41 eV) due to the higher magnetic moment.A large magnetic moment for the Mn atom is predicted to be 3.81μB.We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate,which confirms the experimental results.The magnetism of Mn is identified as the driving force of the large buckling and the work-function change.The comparison with the other magnetic surface alloys is also presented and some trends are predicted.