(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     

WnNim(n+m=8)团簇结构与电子性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在Lanl2dz基组水平上对W_nNi_m(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的平均结合能、Wiberg键级(WBI)、磁学性质、NBO进行了分析,结果表明:团簇随着W原子数的增多,稳定性增强,n≥5时,结构中都含有纯钨团簇的结构基元;W-W键级高于W-Ni键和Ni-Ni键;W₅Ni₃,W₆Ni₂团簇发生了"磁矩猝灭"的现象;在W,Ni原子内部,轨道电荷发生了转移,产生了"轨道杂化"现象,W,Ni原子之间也发生了电荷转移形成了较强的化学键. 关键词： nNi_m(n+m=8)团簇')" href="#">W_nNi_m(n+m=8)团簇 几何结构 电子性质 密度泛函理论     

MgmBn(m=1,2;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Mg_mB_n(m=1,2;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、电离势、成键特性、极化率和超极化率等性质进行了理论研究.结果表明，团簇的最稳定结构大多是平面结构，团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心，而其他B原子和Mg原子通常处在端位，且显正电性；团簇中通常是B-B键和B-Mg键共存，极少出现Mg-Mg键， 关键词： mB_n(m=1')" href="#">Mg_mB_n(m=1 n=1-4)团簇 密度泛函理论 结构与性质     

BaxOy小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质

为了说明钡助剂的存在形式, 本文采用第一性原理方法研究了Ba_xO_y小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质. 基于总能的热力学分析发现, 在实验条件下(500 K, P_H2O/P_H2<10^-3), Ba₂O团簇比BaO₂, BaO, Ba和O等团簇(原子)更加稳定. 这证实含有金属性钡原子的团簇也是氧化钡助剂可能的工作状态. 表面电荷差分密度说明Ba₂O团簇的氧和钡原子与衬底的作用不同. 不过Ba₂O团簇氧和钡原子附近的氮分子吸附行为相似, Ba₂O团簇增强了氮分子和衬底的相互作用. Ba₂O团簇氧和钡原子附近的氮分子吸附能分别为0.78 和0.88 eV, 均大于清洁表面的0.67 eV. 氮分子间距和氮分子的拉伸振动频率都表明Ba₂O团簇在一定程度上活化了吸附氮分子. Ba₂O团簇氧和钡原子附近的N–N键长分别为0.117和0.116 nm, 大于清洁表面的0.114 nm. 氧和钡原子附近氮分子的拉伸振动频率分别为 1888 和1985 cm^-1, 小于清洁表面的2193 cm^-1. 电荷差分密度的计算结果说明, 削弱作用主要来自于Ba₂O团簇中钡离子和氮分子间的静电作用. 两者间的静电作用增加了氮分子π 反键轨道的占据数, 促进了氮分子极化, 从而削弱氮分子键.     

密度泛函理论研究MgnOn(n=2—8)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对Mg_nO_n(n=2—8)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,当n=2,3时,团簇的最低能量结构是平面结构;当n≥4时, 团簇的最低能量结构可以看成是由Mg₂O₂和Mg₃O₃单元组成的三维结构.O—Mg—O的钝角和较多的电荷转移对团簇的稳定性 关键词： nO_n团簇')" href="#">Mg_nO_n团簇 几何结构 电子性质     

Structure and stability of a silicon cluster on sequential doping with carbon atoms

SiC is a highly stable material in bulk. On the other hand, alloys of silicon and carbon at nanoscale length are interesting from both technological as well fundamental view point and are being currently synthesized by various experimental groups (Truong et. al., 2015 [26]). In the present work, we identify a well-known silicon cluster viz., Si₁₀ and dope it sequentially with carbon atoms. The evolution of electronic structure (spin state and the structural properties) on doping, the charge redistribution and structural properties are analyzed. It is interesting to note that the ground state SiC clusters prefer to be in the lowest spin state. Further, it is seen that carbon atoms are the electron rich centres while silicon atoms are electron deficient in every SiC alloy cluster. The carbon–carbon bond lengths in alloy clusters are equivalent to those seen in fullerene molecules. Interestingly, the carbon atoms tend to aggregate together with silicon atoms surrounding them by donating the charge. As a consequence, very few Si–Si bonds are noted with increasing concentrations of C atoms in a SiC alloy. Physical and chemical stability of doped clusters is studied by carrying out finite temperature behaviour and adsorbing O₂ molecule on Si₉C and Si₈C₂ clusters, respectively.     

Fe_nO_m~+(n+m=4)团簇的构型、电子结构特征和磁性

采用二项式方案构建了FenOm+(n+m=4)团簇的大量可能初始结构.运用广义梯度近似(GGA)密度泛函理论中的PW91交换关联泛函对这些初始结构进行优化和频率分析,得到12个稳定的异构体.在此基础上计算和分析了它们的结合能、对称性、键长、磁矩,最高占据轨道与最低未占据轨道的能隙.发现Fe—O键在FenOm+(n+m=4)团簇的稳定中具有重要作用,团簇的总磁矩主要取决于铁原子的磁矩和各个原子磁矩排布情况.     

利用Gupta势结合遗传算法研究ConCu55－n(n=0—55)混合团簇的结构演化及基态能量

采用半经验的Gupta多体势结合遗传算法对Co_nCu_55－n(n=0—55)混合团簇的基态结构和能量进行了研究,发现这些混合团簇的基态结构是在Co₅₅,Cu₅₅单质团簇(Mackay二十面体)的基础之上发生的畸变;从n=0(Cu₅₅)开始,Co原子从中心到表面,从棱到顶点依次、连续替换Cu原子;基态结构与键能较大键的数目及其平均键长有关;Co₁₃Cu₄₂具有最稳定的结构,13个Co原子全部位于团簇内部形成Mackay二十面体对整个团簇的稳定性有显著影响. 关键词： 团簇 结构和能量 Gupta势 遗传算法     

W_n Ni_m(n+m≤7;m=1,2)团簇电子结构与光谱性质的理论研究

采用密度泛函理论(DFT)中的B3PW91方法在LANL2DZ基组水平上对WnNim(n+m≤7;m=1,2)团簇的各种可能构型进行了几何结构优化,得出了它们的基态构型,并对其NBO、振动频率、光谱和极化率进行了理论研究.研究结果表明:W,Ni原子内部杂化现象较强,而在W-Ni原子之间杂化较弱;在W和Ni相互作用形成合金团簇的过程中,发生原子间的电荷转移,使得合金团簇中大多数Ni原子带正电荷W原子带负电荷;从光学上分析显示,W6Ni团簇的IR和Raman谱中的振动峰最多,W5Ni2的IR和Raman谱中的振动峰最强,W2Ni的IR谱中只有一个较强峰值;WnNim(n+m≤7;m=1,2)团簇中原子间的成键相互作用随W成分的增加而增强.     

(Li3N)n(n=1—5)团簇结构与性质的密度泛函研究

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(Li₃N)_n(n=1—5)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、电荷特性等进行了理论研究. 结果表明,(Li₃N)_n(n=1—5)团簇中N原子的配位数以4,5较多见,Li—Li键长为0.210—0.259nm,Li原子在桥位时Li—N键长为0.185—0.204nm,Li原子在端位时Li—N键长为0.172—0.178nm;团簇中N原子的平均自然电荷为-2.01e,Li原子的平均自然电荷为+0.67e;Li₃N,(Li₃N)₅团簇有相对较高的动力学稳定性. 关键词： 3N)_n(n=1—5)团簇')" href="#">(Li₃N)_n(n=1—5)团簇 密度泛函理论 结构与性质 储氢材料     

Indium sputtering upon bombardment with cluster ions

A surface-ionization method is developed for measuring the integral yields of neutral particles sputtered under the effect of ion bombardment. An investigation is performed to compare the integral yield of particles sputtered upon bombarding indium with Bi _m ⁺ cluster ions (m = 1?C7) in the energy range of 2?C10 keV and the secondary ion emission under bombardment with Bi _m ⁺ cluster ions (m = 1?C5) in the energy range of 6?C18 keV. A nonadditive increase in the indium sputtering coefficient is observed with an increasing number of atoms in the bombarding clusters.     

Sr and Ga substituted Ba2In2O5: Linking ionic conductivity and the potential energy surface

We study in detail the potential energy surface of Ga and Sr substituted Ba₂In₂O₅ by considering the changes in the relative energies of the local structures of Ba₂In₂O₅ when replacing 1 / 8th of the indium atoms with gallium or 1 / 8th of the barium atoms with strontium. The calculations are subsequently used to interpret the increase in ionic conductivity of cubic Ba₂In₂O₅ when strontium is substituted for barium and the decrease in ionic conductivity when gallium is substituted for indium. The effects of replacing 1 / 8th of the indium atoms with gallium or 1 / 8th of the barium atoms with strontium are significant and affect considerably the relative stability of the different low energy local structures present for Ba₂In₂O₅. While a higher density of low energy structures is observed for Ba_1.75Sr_0.25In₂O₅ than for Ba₂In₂O₅, the opposite occurs for Ba₂In_1.75Ga_0.25O₅. This observation supports our main hypothesis: a high density of low energy local structures is a prerequisite for high ionic conductivity.     

A. C. behaviour and dielectric relaxation in indium oxide films

Vacuum deposited blackish indium oxide films (In-O) as well as the oxidised films (In₂O₃) were studied for their a.c. behaviour at different temperatures and at various film thicknesses in the audio frequency region. ε of In-O films was thickness dependent and also showed dielectric relaxation at lower frequencies due to the dipolar orientation arising from their non-stoichiometric nature. However at liquid nitrogen temperature region ε was thickness independent similar to the oxidised films which neither showed any relaxation effect nor any thickness dependent ε. The results have been discussed from the classical theory of dielectric polarisation.     

Cu吸附(SiO3)n(n=1—8)团簇几何结构和电子性质的密度泛函研究

运用密度泛函理论下的广义梯度近似和交换关联函数对Cu吸附(SiO₂)n(n=1—8)团簇的几何结构、电荷分布、稳定性和电子性质进行了较详细的研究,结果表明: Cu原子易于和带有悬挂键的Si原子作用并形成"铜岛膜"; Cu吸附(SiO₂)_n团簇后Si原子失去电子能力减弱,O原子得到电子能力增强;Cu(SiO₂)n(n 关键词： 密度泛函理论 2)_n (n=1—8)团簇')" href="#">Cu(SiO₂)_n (n=1—8)团簇 近红外吸收     

Oxidation of indium implanted aluminium studied by the Rutherford backscattering and perturbed angular correlation methods

Aluminium foils oversaturated with 5.10¹⁵/cm² implanted¹¹⁵In⁺ ions were oxidized in 200 mbar oxygen or vacuum annealed at 370–870 K. The samples were analyzed by the Rutherford backscattering (RBS) and perturbed angular correlation (PAC) techniques, using some 10¹¹/cm² implanted radioactive¹¹¹In tracers. Furthermore, the oxygen surface profiles were also scanned with high resolution by using the nuclear resonance technique (NRA). The formation of passivating Al₂O₃ surface layers, preventing deeper oxygen diffusion and the indium diffusion into these oxidized surface layers and into the bulk, were studied. Several quadrupole interaction frequencies previously attributed to strained cubic indium precipitates and indium (-vacancy) clusters were observed. When the samples were oxidized above 750 K, the formation of In-O complexes and of substitutional¹¹¹In in Al₂O₃ was observed.     

Charge transfer between alkali cluster ions and atoms in the 1 to 10 keV collisional energy range

The cross-sections for collisional charge transfer between singly charged free clusters M _n ⁺ (M = Li, Na; n=1...50) and atomic targets A (cesium, potassium) have been measured as a function of collisional relative velocity in laboratory energy range 1–10 keV. For each cluster size, the experimental values of the charge transfer cross-section are fitted with an universal parametric curve with two independent parameters and v_m, the maximum cross-section and the corresponding velocity. For small size clusters (), the characteristic parameters show strong variations with the number of atoms in the cluster. Abrupt dips observed for n=10 and n=22 are attributed to electronic properties. Charge transfer patterns observed for various collisional systems present similarities, which appear more sensitive to cluster quantum size effects than to collision energy defects. In their whole, the and v_m parameters show differences in both their size evolution and their absolute values discussed in term of projectile and target electronic structures. Received 13 April 2000 and Received in final form 29 June 2000     

［Mg(NH2)2］n(n=1—5)团簇的密度泛函理论研究

用密度泛函理论的杂化密度泛函B3LYP方法在6-31G^*基组水平上对［Mg(NH₂)₂］_n(n=1—5)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.对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究.结果表明：团簇易形成链状结构,Mg—N键长为0.190—0.234 nm,N—H键长为0.101—0.103 nm,H—N—H键角为100.2°—107.5°;团簇中M 关键词： 2)₂］_n(n=1—5)团簇')" href="#">［Mg(NH₂)₂］_n(n=1—5)团簇 密度泛函理论 结构与性质 储氢材料     

Addition complex and insertion isomers on the potential energy surface of the reaction of indium dimer with water studied with relativistic ECP

Stationary points on the lowest singlet and triplet In₂ + H₂O potential energy surfaces (PESs) have been explored using the coupled cluster method, including single and double excitations with perturbative triples (CCSD(T)), and the density functional theory (DFT), employing the effective core potential (ECP) for indium (In), which accounts for scalar relativistic effects, with the triple-zeta quality basis set. The CCSD(T) calculated binding energy and anharmonic ν₂-bending mode frequency for the triplet ground-state addition complex, In₂^… OH₂(³B₁), are consistent with the complex detected in the matrix isolation infrared (IR) spectroscopic study under the thermal conditions. The two minimum energy crossing points between the triplet and the singlet PESs that have been located between the structures of In₂^…OH₂ and the transition state for the O–H bond breakage are not likely to be thermally accessible under the low-temperature matrix conditions. With the CCSD(T)-calculated In₂ + H₂O reaction profile and anharmonic vibrational frequencies for several In₂(H)(OH) insertion product isomers, we support the IR matrix isolation detection (by two experimental groups) of the lowest energy singlet double-bridged In(μ-H)(μ-OH)In isomer. For the proposed two-step mechanism of H₂ elimination from the In₂(H)(OH) species, the estimated energy barriers are also compatible with experiment.     

Structural,energetic, and electronic properties of hydrogenated aluminum arsenide clusters

The chemisorptions of hydrogen on aluminum arsenide clusters are studied with density functional theory (DFT). The on-top site is identified to be the most favorable chemisorptions site for hydrogen. And the Al-top site is the preferred one in the most cases for one hydrogen adsorption in (AlAs) _n (n = 2, 5, 6, 8–15) clusters. Top on the neighboring Al and As atoms ground-state structures are found for two hydrogen adsorption on (AlAs) _n except for (AlAs)₂ cluster. The Al–As bond lengths decrease generally as the size of the cluster increases. And there is a slight increase in the mean Al–As bond lengths after H adsorption on the lowest-energy sites of the most AlAs clusters. In general, the binding energy of H and 2H are both found to decrease with an increase in the cluster size. And the result shows that large binding energies (BE) of a single hydrogen atom on small AlAs clusters and large highest occupied and lowest unoccupied molecular-orbital gaps for (AlAs)H and (AlAs)₃H make these species behaving like magic clusters. Calculations on two hydrogen atoms on (AlAs) _n clusters show large BE for (AlAs) _n H₂ with an odd number of n. The stability of these complexes is further studied from the fragmentation energies. (AlAs)₇H₂ and (AlAs)₉H₂ clusters are again suggested to be the stable clusters. On the other hand both the fragmentation energy and the binding energy for (AlAs)₁₃H are close to the lowest values.     

密度泛函理论研究ScnO(n=1—9)团簇的结构、稳定性与电子性质

采用基于密度泛函理论的BP86/CEP-121G （O原子采用6-311G^**基组）方法,对Sc_nO （n=1—9）团簇的几何结构、能量与稳定性、电子结构性质及其随团簇尺寸的变化趋势进行了研究.随着团簇原子个数的增加,O原子从位于Sc_n团簇结构的边缘转变为占据团簇的内部位置.O原子的掺入增加了Sc_n团簇的稳定性,使其能隙升高,并改变了其稳定性及电子结构性质随团簇尺寸变化的规律;含有偶数个Sc原子的氧化物团簇比其周围邻近的含有奇数个Sc原子的氧化物团簇具有相对较高的稳定性.Sc_nO团簇电离势的理论计算值与实验值符合得较好,而其电子亲和势呈现振荡交替上升的变化趋势;用最大化学硬度规律等方法表征了Sc_nO氧化物团簇的稳定性和电子结构性质. 关键词： nO团簇')" href="#">Sc_nO团簇 几何结构 电子性质 密度泛函理论