三元层状陶瓷M-Al-N(M=Ti,Zr,Hf)的结构及力学性质的第一性原理模拟

基于第一性原理方法，探索M-Al-N（M=Ti，Zr，Hf）结构的稳定性，计算其力学性质.计算M-Al-N化合物的能量，发现除实验已知的结构Ti₂AlN和Ti₄AlN₃、Zr₂AlN、Hf₂AlN外，还存在两种新的热力学稳定结构Zr₄AlN₃、Hf₄AlN₃.弹性常数和声子谱的计算，表明这两个结构是力学稳定和晶格动力学稳定的.计算M₂AlN和M₄AlN₃的力学性质，发现它们具有高的体模量、剪切模量、弹性模量、维氏硬度等；分析其力学性质随组分比例、组成元素的变化规律，为该类材料的选择和应用提供理论依据.最后计算M₂AlN和M₄AlN₃的电子态密度和分态密度、电子密度分布、Mulliken群分析等.     

(K3N)n(n=1,…,5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论B3LYP方法,在6-311G*水平上对碱金属氮化物(K₃N)_n(n=1,…,5)团簇各种可能构型进行几何结构优化,预测各团簇的最稳定结构,并对其成键特性、电荷分布、振动特性及稳定性进行分析研究.结果表明,随着n的增大,(K₃N)_n(n=1,…,5)团簇的最稳定结构逐渐由平面结构向空间立体结构转变,(K₃N)₄、(K₃N)₅团簇为类似晶体的层状结构;团簇中N原子的配位数以5、6较多见;团簇中N原子的平均自然电荷为-1.608e,K原子的平均自然电荷为+0.550e,K-N键为较强的离子键;(K₃N)₄团簇有相对较高的动力学稳定性.     

V,Cr,Mn掺杂MoS2磁性的第一性原理研究

基于第一性原理的自旋极化密度泛函理论分别研究了过渡金属V, Cr, Mn掺杂单层MoS₂的电子结构、 磁性和稳定性. 结果表明: V和Mn单掺杂均能产生一定的磁矩, 而磁矩主要集中在掺杂的过渡金属原子上, Cr单掺杂时体系不显示磁性. 进一步讨论双原子掺杂MoS₂ 体系中掺杂原子之间的磁耦合作用发现, Mn掺杂的体系在室温下显示出稳定的铁磁性, 而V掺杂则表现出非自旋极化基态. 形成能的计算表明Mn掺杂的MoS₂体系相对V和Cr 掺杂结构更稳定. 由于Mn掺杂的MoS₂ 不仅在室温下可以获得比较好的铁磁性而且其稳定性很高, 有望在自旋电子器件方面发挥重要的作用. 关键词： 2')" href="#">单层MoS₂ 掺杂 铁磁态 第一性原理     

Hf-N体系的晶体结构预测和性质的第一性原理研究

为了寻找具有优异力学性能的新型超高温陶瓷材料, 结合进化算法和第一性原理, 系统研究了Hf-N二元体系所有稳定存在的化合物及其晶体结构. 除了实验已知的岩盐结构的HfN之外, 本文还找到了Hf₆N(R-3), Hf₃N(P6₃22), Hf₃N₂(R-3m), Hf₅N₆(C2/m)和Hf₃N₄(C2/m)五种新结构, 基于准简谐近似原理计算了这些稳定结构的声子谱以验证其动力学稳定性, 常温甚至更高温度下的吉布斯自由能以验证其高温热力学稳定性. 结果表明, 这些结构是动力学稳定的, 且在1500 K以下都是热力学稳定的. 同时, 本文还列出了在搜索过程中出现的空间对称性较高、能量较低的亚稳态结构, 包括Hf₂N(P4₂/mnm), Hf₄N₃(C2/m), Hf₆N₅(C2/m), Hf₄N₅(I4/m), Hf₃N₄(I-43d)和Hf₃N₄(Pnma). 之后计算了上述所有结构的力学性质(弹性常数、体模量、 剪切模量、 杨氏模量、硬度), 随着N 所占比例的增加, 硬度呈现的整体趋势是先增大后下降, 在Hf₅N₆处取得最大值, 为21 GPa. 其中Hf₃N₂和Hf₄N₅也展现出了较高的硬度, 都为19 GPa. 最后, 计算了这些结构的电子态密度和晶体轨道汉密尔顿分布, 从电子结构的角度分析了力学性能的成因. 研究结果显示, 较强的Hf-N共价键和较低的结构空位率是Hf₅N₆具有优异力学性能的主要原因.     

Cu掺杂β-Si3N4的力学性能和电子结构的第一性原理研究

采用基于密度泛函的第一性原理方法研究了(Si_3-xCu_x)N₄(x=0,0.25,0.5,0.75,1)晶体的稳定性、力学性能和电子结构,分析了Cu掺杂对β-Si₃N₄力学性能的影响机制.结果表明,(Si_3-xCu_x)N₄为热力学稳定结构,Cu掺杂降低了β-Si₃N₄的稳定性.由弹性常数和Voigt-Reuss-Hill近似看出,(Si_3-xCu_x)N₄满足波恩力学稳定性判据,Cu掺杂使得β-Si₃N₄的体模量、剪切模量和杨氏模量降低,当x=0时,(Si_3-xCu_x)N₄的体模量、剪切模量和杨氏模量最大,分别为234.3 GPa、126.7 GPa和322.1 GPa.根据泊松比和G/B值判断出(...     

5d过渡金属二硼化物的结构和热、力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理系统地研究了5d过渡金属二硼化物TMB₂ (TM=Hf–Au) 的结构、热学、力学和电学性质. 我们考虑了三种结构, 分别为AlB₂, ReB₂和WB₂结构. 计算得到的晶格常数与先前的理论和实验研究符合得很好. 通过计算生成焓预测了化合物的热力学稳定性; 从HfB₂到AuB₂, 生成焓的整体趋势是逐渐增加的. 在所考虑的结构中, 对HfB₂和TaB₂, AlB₂结构是最稳定的; 对WB₂, ReB₂, OsB₂, IrB₂和AuB₂, ReB₂结构是最稳定的; 对PtB₂, WB₂结构是最稳定的. 在所考虑的化合物中, ReB₂结构的ReB₂具有最大的剪切模量(295 GPa), 是最硬的化合物, 与先前的理论和实验结果相符. 计算得到的总态密度显示所有结构都具有金属特性. 讨论了系列化合物的变化趋势. 关键词： 弹性性质 热力学性质 第一性原理 5d过渡金属二硼化物     

(HMgN3)n(n=1–5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G^*水平上对叠氮化合物(HMgN₃)_n(n=1–5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构. 并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究. 结果表明:HMgN₃团簇最稳定结构为直线型;(HMgN₃)_n(n=2,5)团簇最稳定结构为叠氮基中N原子和金属原子相连构成Mg–N–Mg结构;(HMgN₃)_n(n=3,4)团簇最稳定结构为叠氮基与Mg原子相互链接形成的环状结构. 团簇最稳定结构中金属Mg原子均显示正电性,H原子均显示负电性,叠氮基中间的N原子显示正电性、两端的N原子显示负电性,且与Mg原子直接作用的N原子负电性更强. Mg–N键和Mg–H键为典型的离子键,叠氮基内N原子之间是共价键. 团簇最稳定结构的红外光谱分为三部分,其最强振动峰均位于2258–2347 cm^-1,振动模式为叠氮基中N–N键的反对称伸缩振动. 叠氮基在团簇和晶体中结构不变,始终以直线型存在. 稳定性分析显示,(HMgN₃)₃团簇相对于其他团簇更为稳定. 关键词： 3)_n(n=1–5)团簇')" href="#">(HMgN₃)_n(n=1–5)团簇 叠氮基 密度泛函理论 结构与性质     

Co和稳定元素对Nd3(Fe,Co,M)29(M=Ti,V,Cr) 化合物结构和磁性的影响

利用x射线衍射和磁测量研究了不同稳定元素Co以及Ti,V和Cr替代对Nd₃Fe_29-x-yCo_xM_y(M=Ti,V,Cr)化合物结构和磁性的影响.研究发现:每一个稳定元素都有一替代量极限,在此极限以内所有化合物均为Nd₃(Fe,Ti)₂₉型结构,A2/m空间群.不同稳定元素的溶解极限不同.Co的替代量与稳定元素有关,当以Cr作为稳定元素时,Cr的替代量随着Co含量的提高而提高 关键词： 3(Fe')" href="#">Nd₃(Fe Co 29')" href="#">M)₂₉ 结构 磁性     

(Ti1-xNbx)5AlC4(x=0.4, 0.75, 1)固溶体系的第一性原理研究

采用第一性原理计算，通过投影缀加波(PAW)和广义梯度近似(GGA)研究三元层状化合物(MAX) Ti₅AlC₄中Nb多比例掺杂M位元素.通过计算该固溶体系的声子谱、生成焓和弹性常数，讨论了(Ti_1-xNb_x)₅AlC₄固溶体系的稳定性，得到了三种稳定的结构：(Ti_0.6Nb_0.4)₅AlC₄、(Ti_0.25Nb_0.75)₅AlC₄和Nb₅AlC₄,即(Ti_1-xNb_x)₅AlC₄(x=0.4, 0.75, 1)固溶体系.Bader电荷、局域电荷密度、态密度表明该固溶体系呈现出金属特性，且电导率随着掺杂比例的增大，电荷不断转移，电导率增强.通过计算不同掺...     

(Ca3N2)n(n=1—4)团簇结构与性质的密度泛函理论研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G^*基组水平上对(Ca₃N₂)_n(n=1—4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、成键特性、电荷特性和稳定性等进行了理论分析.结果表明,(Ca₃N₂)_n(n=1—4)团簇最稳定构型中N原子为3—5配位,Ca—N键长为0.231—0.251nm,Ca—Ca键长为0.295—0.358nm;N原子的自然电荷在-1.553e—-2.241e之间,Ca原子的自然电荷在1.035e—1.445e之间,Ca和N原子间相互作用呈现较强的离子性,Ca₃N₂和(Ca₃N₂)₃团簇有相对较高的动力学稳定性. 关键词： 3N₂)_n(n=1—4)团簇')" href="#">(Ca₃N₂)_n(n=1—4)团簇 密度泛函理论 结构与性质     

Mass spectrometric and thermodynamic studies of vapor-phase growth of In(1−x)GaxP

A time-of-flight mass spectrometer was coupled directly to an open tube vapor growth system. The vapor composition and the processes occurring during the deposition of In_(1?x)Ga_xP alloys were studied. It was found that the vapor species present in this system are InCl, GaCl, HCl, PH₃, P₂, P₄ and H₂. The deviations from the chemical equilibrium in the system were determined and measured.A chemical equilibrium model was set and used to calculate the equilibrium partial pressures of all species under a wide range of experimental conditions. These calculations were used to predict successfully the proper conditions for growth of desired In_(1?x)Ga_xP alloys.     

The structure and the potential energy function of AlSO(C_S,X~2A″)

By using the B3P86/aug-cc-pvtz method,the accurate equilibrium geometry of the AlSO(CS,X2A″) molecule has been calculated and compared with available theoretical values.The obtained results show that the AlSO molecule has a most stable structure with bond lengths of R OAl = 0.1864 nm,R OS = 0.1623 nm,R AlS = 0.2450 nm,together with a dissociation energy of 13.88 eV.The possible electronic states and their reasonable dissociation limits for the ground state of the AlSO molecule were determined based on the principle of atomic and molecular reaction statics.The analytic potential energy function of the AlSO molecule was derived by the many-body expansion theory and the contour lines were constructed for the first time,which show the internal information of the AlSO molecule,including the equilibrium structure and stable point.The analysis demonstrates that the obtained potential energy function of AlSO is reasonable and successful and the present investigations provide important insights for further study on molecular reaction dynamics.     

Isomerization of C3H3NO isomers: ab initio study

The structures and isomerization process of C₃H₃NO species have been explored at the MP2/6–311++G(d,p) level of theory of the ab initio method. Eleven minima and four interconversion transition states have been identified. The zero-point vibrational energy corrections were made to predict reliable energies. We predict a five-membered ring-like structure to be the lowest energy isomer, which is 177.73?kcal?mol^?1 more stable than the least stable isomer X found on the potential energy surface. The transition states and minima isomers were verified by frequency calculation. Intrinsic reaction coordinate (IRC) calculations have been performed to confirm that each transition state is linked by the desired reactants and products. The isomer stabilities have been studied using the relative energies, chemical hardness and chemical potential. The MHP principle could not predict the order of stability for C₃H₃NO isomers as arrived at with the relative energies. The role of intramolecular hydrogen bonds on the equilibrium structure has been discussed. The energy barrier and reaction enthalpy have been calculated during isomerization.     

First-principles investigation of the intrinsic defects in Ti3SiC2

First-principles calculations have been carried out to investigate intrinsic defects including vacancies, interstitials, antisite defects, Frenkel and Schottky defects in the 312 MAX phase Ti₃SiC₂. The formation energies of defects are obtained according to the elemental chemical potentials which are determined by the phase stability conditions. The most stable self-interstitials are all found in the hexahedral position surrounded by two Ti(2) and three Si atoms. For the entire elemental chemical potential range considered, our results demonstrated that Si and C related defects, including vacancies, interstitials and Frenkel defects are the most dominant defects. Besides, the present calculations also reveal that the formation energies of C and Si Frenkel defects are much lower than those of all Schottky defects considered. In addition, the calculated profiles of densities of states for the defective Ti₃SiC₂ indicate that these defects should have great influence on its thermal and electrical properties.     

Defect chemical and statistical thermodynamic studies on oxygen nonstoichiometric Nd2 − xSrxNiO4 + δ

In order to elucidate how oxygen content changes in Nd_2 − xSr_xNiO_4 + δ (x = 0, 0.2, 0.4), defect chemical and statistical thermodynamic analyses were carried out. The relationship among δ, P(O₂), and T were analyzed by a defect equilibrium model. Since Nd_2 − xSr_xNiO_4 + δ shows metal like band conduction at high temperatures, chemical potential of hole is expressed by the integration of the Fermi-Dirac distribution function and the density of state. The nonstoichiometric variation of oxygen content in Nd_2 − xSr_xNiO_4 + δ can be explained by the defect equilibrium model with a regular solution approximation. Partial molar entropy and partial molar enthalpy of oxygen are calculated from the nonstoichiometric data and Gibbs–Helmholtz equation. The relationship among defect structure, defect equilibrium, and thermodynamic quantities is elucidated by the statistical thermodynamic model. Thermodynamic quantities are calculated by the statistical thermodynamic model with the results of defect chemical analysis and compared with those obtained from experimental results. Thermodynamic quantities calculated by the statistical thermodynamic model can explain rough tendency of those obtained from the δ–T–P(O₂) relationship.     

用耦合簇理论及相关一致五重基研究SiH$lt;sub$gt;2$lt;/sub$gt;($lt;i$gt;X$lt;/i$gt;$lt;sup$gt;1$lt;/sup$gt;$lt;i$gt;A$lt;/i$gt;$lt;sub$gt;1$lt;/sub$gt;)自由基的解析势能函数

运用单双迭代三重激发耦合簇理论和相关一致五重基对SiH₂的基态结构进行了优化, 并在优化结构的基础上进行了离解能和振动频率的计算. 结果表明: SiH₂的基态为C_2v结构, 平衡核间距R_Si—H= 0.15163 nm, H—Si—H键的键角α=92.363°, 离解能D_e（HSi—H）=3.2735 eV, 频率ν₁（a₁）=1020.0095 cm^-1, ν₂（a₁）=2074.8742 cm^-1, ν₃（a₁）=2076.4762 cm^-1. 这些结果与实验值均较为相符. 对H₂的基态使用优选出的cc-pV6Z基组、对SiH的基态使用优选出的aug-cc-pV5Z基组进行几何构型与谐振频率的计算并进行单点能扫描, 且将扫描结果拟合成了解析的Murrell-Sorbie函数. 与实验结果及其他理论计算结果的比较表明, 本文关于SiH自由基光谱常数（D_e,R_e, ω_e, B_e, α_e和ω_eχ_e）的计算结果达到了很高的精度. 采用多体项展式理论导出了SiH₂（C_2v, X¹A₁）自由基的解析势能函数, 其等值势能图准确再现了它的离解能和平衡结构特征. 同时还给出了SiH₂（C_2v, X¹A₁）自由基对称伸缩振动等值势能图中存在的两个对称鞍点, 对应于SiH+H→SiH₂反应, 势垒高度为0.5084 eV. 关键词： 2')" href="#">SiH₂ Murrell-Sorbie函数 多体项展式理论 解析势能函数     

ZnO/MoO3 mixed oxide nanotube: A highly efficient and stable catalyst for degradation of dye by air under room conditions

As a continuation of our work to develop catalysts with high activity for catalytic air wet oxidation process under mild conditions, degradation of wastewater containing 0.3 g/L Safranin-T (ST) by air oxidation over ZnO/MoO₃ nanotube catalyst was studied. It was found the decolorization efficiency and the chemical oxygen demand (COD) removal of ST reached above 98% and 95%, respectively, within 18 min at room temperature and atmospheric pressure. And the organic pollutants were totally mineralized to simple inorganic species such as HCO₃⁻, Cl⁻ and NO₃⁻, while the total organic carbon (TOC) decreased 99.3%. The structure and morphology of the catalyst after ten cycling runs showed that the catalyst was stable under such operating condition and the leaching test showed negligible leaching effect. This ZnO/MoO₃ nanotube is proved to be an active and stable heterogeneous catalyst in CWAO of ST under extremely mild conditions.     

First-principles study of electronic properties and stability of Nb5SiB2（001） surface

The density functional calculations are performed to study the electronic structure and stability of Nb 5 SiB 2(001) surface with different terminations.The calculated cleavage energies along the(001) planes in Nb 5 SiB 2 are 5.015 J · m 2 and 6.593 J · m 2 with the break of Nb-Si and Nb-NbB bonds,respectively.There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy:the larger the cleavage energy,the larger the surface relaxation.Moreover,the surface stability of the Nb 5 SiB 2(001) with different terminations has been investigated by the chemical potential phase diagram.From a thermodynamics point of view,the four terminations can be stabilized under different conditions.In chemical potential space,NbB(Nb) and Nb(Si) terminations are just stable in a small area,whereas Si(Nb) and Nb(NbB) terminations are stable in a large area(the letters in brackets represent the subsurface atoms).     

Structures and electronic properties of Mo2nNn（n=1-5）:a density functional study

The lowest-energy structures and the electronic properties of Mo2nNn(n=1-5) clusters have been studied by using the density functional theory(DFT) simulating package DMol 3 in the generalized gradient approximation(GGA).The resulting equilibrium geometries show that the lowest-energy structures are dominated by central cores which correspond to the ground states of Mo n(n = 2,4,6,8,10) clusters and nitrogen atoms which surround these cores.The average binding energy,the adiabatic electron affinity(AEA),the vertical electron affinity(VEA),the adiabatic ionization potential(AIP) and the vertical ionization potential(VIP) of Mo2nNn(n=1-5) clusters have been estimated.The HOMO-LUMO gaps reveal that the clusters have strong chemical activities.An analysis of Mulliken charge distribution shows that charge-transfer moves from Mo atoms to N atoms and increases with cluster size.     

Structural and spectroscopic properties of small Pun （n= 2-5） molecules

The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pu_n (n=2-5) molecules are systematically investigated using the methods of general gradient approximation (GGA) of density functional theory (DFT). The results show that the bond length of the lowest-energy structure of Pu₂ is 2.578 AA. The ground state structure of Pu₃ is a triangle with D_3h symmetry, whereas for Pu₄, the ground state structure is a square (D_4h) and the spin polarization of 16 for molecule Pu₅ with square geometry (D_4h) is the most stable structure. For the ground state structures, the vibrational spectra as well as thermodynamic parameters are worked out. In addition, the values for the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) along with the energy gap of all the Pu_2-5 structures are presented. The relevant structural and chemical stabilities are predicted.