计算机模拟原子簇的稳定构型和能量性质

用密度泛函(DFT)方法研究了铜原子簇Cu~n(n=2,3,4,6)的稳定几何构型和电子结构。通过拟合从头算势能面构造铜原子簇势能函数的双体、三体及四体项，并利用该函数和全局优化“Basin-Hopping”算法得到较大铜原子簇(n=13～56)能量极小的结构，计算结果与实验及其它计算结果相一致。     

计算机模拟铌原子簇的稳定构型和能量性质

采用密度泛函(DFT)方法结合全局优化"Basin-Hopping"算法研究了铌原子簇: 对于Nb小簇n＝2～6我们用密度泛函方法计算了它们的稳定几何构型和电子结构, 通过拟合计算结果构造铌原子簇势能函数, 并利用该函数和全局优化"Basin-Hopping"算法得到较大铌原子簇(n＝7～20)能量极小的结构. 计算结果表明与实验及其它计算结果相一致.     

锡原子簇的结构和相对稳定性

基于从固体锡确立的多体展开势能函数, 采用座标直接优化方法预测了锡原子簇分子(Sn_2-Sn_(300))的结构和相对稳定性, 并用蒙特卡罗方法验证了有关小的原子簇(Sn_2-Sn_(15))的所有结果. 优化结果表明: (1)小的锡原子簇分子(Sn_2-Sn_(15))倾向于密堆积结构, 与锡晶体结构无关; (2)中等大小的簇分子, 如Sn_(47), Sn_(71), Sn_(87)及Sn_(147)等, 则呈α-Sn晶体的畸变结构, 其外围各层原子到中心原子的距离受到压缩, 且某些层被劈裂为两层或多层; (3)随着原子簇尺寸的进一步增大, 结构畸变逐渐减弱, 簇分子的单原子平均结合能缓慢增大, 其外椎值大约在Sn_(740)处趋近于α-Sn的结合能.     

Si4X(X=C,N,O,Si,P,S)原子簇结构的理论研究

在密度泛函B3LYP/6-311G*水平上, 对具有C3v对称的Si4X (X = C, N, O, P, S)原子簇进行了几何构型优化计算, 并讨论它们的热力学稳定性、动力学活性、Mulliken布居、SiX键长、占据价轨道的对称性以及HOMO能级位置等周期递变规律。     

PH2^+基态及低激发态的构型优化及光谱性质理论研究

本文报道了PH2^+的一组新的ab initio计算结果。给出了PH2^+的基态(X^1A1)及几个低激发态的电子结构和几何构型。这些态的稳定构型都是在MRSD CI水平上优化得到的。在此基础上, 确定了基态到这些低激发态的跃迁能和部分跃迁的振子强度和辐射寿命。     

杂硼原子簇XB6+ (X=C,Si, Ge,Sn, Pb)的稳定性和芳香性

利用从头算MP2方法和密度泛函理论B3LYP和B3PW91方法, 研究了杂硼原子簇XB₆⁺ (X=C, Si, Ge, Sn, Pb)的结构、稳定性及化学键合情况. 对C, Si, Ge, B使用6-311+G(d)基组, 对Sn和Pb使用LANL2DZ赝势基组. 研究结果表明, 具有C_s对称性的假平面XB₆⁺ (X=C, Si, Ge, Sn, Pb)结构是势能面上的全域极小点, 其稳定性要高于C_6v对称性的锥形结构和C₂对称性的假锥形结构. 在B3LYP水平上, 对这些异构体的势能面的极小点进行了自然键轨道(NBO)的分析; 对最稳定构型的最高占据分子轨道(HOMO)和最低空轨道(LUMO)能级差、分子轨道(MO)和核独立化学位移(NICS)进行了计算和讨论. 分析了杂原子和硼原子间、相邻硼原子间的键合情况, 讨论了最稳定构型的芳香性质.     

铅硫二元团簇Pb~nS~n~-~1^+ (n=2～4)的从头算研究

用密度泛函方法,对铅硫团簇Pb~nS~n~-~1^+(n=2～4)的各种可能的异构体进行计算。结果表明异构体Pb~S^+(C~2~v)、Pb~3S~2^+(C~2~v)和Pb~4S~3^+(C~3~v)最为稳定,是该类团簇系列中最稳定的存在形式。同时,该类团簇的最低空轨道(LUMO)能量较低,容易得到电子,表明其相应的中性团簇也能稳定存在。     

银表面甲醇氧化反应机理的ab initio计算研究 1: 银表面静态吸附物种的几何构型和吸附性质

本文用原子簇模型(CM)的从头计算方法, 计算了银表面甲醇氧化反应中的静态吸附物种的优化几何构型及吸附性质。计算表明在清洁银表面甲醇、甲醛只存在物理吸附; 当表面存在吸附氧原子时, 甲醇可在银表面形成两种分子态吸附;甲醛与表面羟基OH(a)或氢原子H(a)共存时在银表面能够形成化学吸附, 且CH2O(a)极易与O(a)反应生成深度氧化中间体η^2-甲二氧基; 中间产物甲氧基在无氧的银表面能够形成稳定吸附, 在富氧银表面极易进一步氧化脱氢生成产物甲醛。通过计算与实验结果的对照, 我们对反应机理作了初步讨论。     

杂硼原子簇B6X-(X=N, P, As, Sb, Bi)稳定性和芳香性研究

利用Gaussian 98程序, 采用从头算和密度泛函理论方法, 对B6X-(X=N, P, As, Sb, Bi)杂硼原子簇进行了理论研究, 优化得到了其稳定平衡构型, 讨论了其振动光谱和稳定性等, 通过自然键轨道(NBO)、分子轨道(MO)和核独立化学位移(NICS)分析, 确定这些杂硼原子簇都有离域的π电子和σ电子成键轨道, 满足4n+2电子规则, 具有芳香性, 与纯B6- 或B62- 原子簇呈反芳香性不同.     

银表面甲醇氧化反应机理的ab initio计算研究 1: 银表面静态吸附物种的几何构型和吸附性质

本文用原子簇模型(CM)的从头计算方法, 计算了银表面甲醇氧化反应中的静态吸附物种的优化几何构型及吸附性质。计算表明在清洁银表面甲醇、甲醛只存在物理吸附; 当表面存在吸附氧原子时, 甲醇可在银表面形成两种分子态吸附;甲醛与表面羟基OH(a)或氢原子H(a)共存时在银表面能够形成化学吸附, 且CH2O(a)极易与O(a)反应生成深度氧化中间体η^2-甲二氧基; 中间产物甲氧基在无氧的银表面能够形成稳定吸附, 在富氧银表面极易进一步氧化脱氢生成产物甲醛。通过计算与实验结果的对照, 我们对反应机理作了初步讨论。     

Structural and energetic exploration of a boron‐rich sulfide cluster B6S

Boron and mixed‐boron clusters have received considerable attention because of their wide applications and their essential roles in advancing chemical bonding models. Bearing the bright prospects as building blocks to form novel polymeric materials, the sulfur‐rich boron sulfides have been greatly studied. However, the knowledge of the boron‐rich boron sulfides is much rare. In this article, we report an extensive theoretical study on the structural, energetic, and stability features of a hitherto unknown septa‐atomic cluster B₆S at the CCSD(T)/6‐311+G(2df)//B3LYP/6‐311+G(d) level. The local minimum isomers were obtained through our recently developed program “grid‐based comprehensive isomeric search algorithm.” The results show that the planar knife‐like isomer B₅(?BS) 01 (0.0 kcal/mol) containing the ?BS moiety is the lowest energy, followed by the quasi‐planar belt‐like isomer B₆(>S) 02 (6.7 kcal/mol) and the pyramid‐like isomer B₆(>S) 03 (8.4 kcal/mol). Notably, the three singlet isomers all have good kinetic stability on the basis of the potential energy surface analysis. The B/S‐centered wheel‐like isomers are unfavorable in thermodynamics and kinetics. The triplet state structures generally can not compete with the singlet ones. The results are compared to the analogous and isoelectronic cluster B₆O. Our work is expected to provide useful information for understanding the structures and stability of boron sulfides. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Optimization of bimetallic Cu–Au and Ag–Au clusters by using a modified adaptive immune optimization algorithm

A modified adaptive immune optimization algorithm (AIOA) is designed for optimization of Cu–Au and Ag–Au bimetallic clusters with Gupta potential. Compared with homoatom clusters, there are homotopic isomers in bimetallic cluster, so atom exchange operation is presented in the modified AIOA. The efficiency of the algorithm is tested by optimization of Cu_nAu_38‐n (0 ≤ n ≤ 38). Results show that all the structures with the putative global minimal energies are successfully located. In the optimization of Ag_nAu_55‐n (0 ≤ n ≤ 55) bimetallic clusters, all the structures with the reported minimal energies are obtained, and 36 structures with even lower potential energies are found. On the other hand, with the optimized structures of Cu_nAu_55‐n, it is shown that all 55‐atom Cu–Au bimetallic clusters are Mackay icosahedra except for Au₅₅, which is a face‐centered cubic (fcc)‐like structure; Cu₅₅, Cu₁₂Au₄₃, and Cu₁Au₅₄ have two‐shell Mackay icosahedral geometries with I_h point group symmetry. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

The READY program: Building a global potential energy surface and reactive dynamic simulations for the hydrogen combustion

READY (REActive DYnamics) is a program for studying reactive dynamic systems using a global potential energy surface (PES) built from previously existing PESs corresponding to each of the most important elementary reactions present in the system. We present an application to the combustion dynamics of a mixture of hydrogen and oxygen using accurate PESs for all the systems involving up to four oxygen and hydrogen atoms. Results at the temperature of 4000 K and pressure of 2 atm are presented and compared with model based on rate constants. Drawbacks and advantages of this approach are discussed and future directions of research are pointed out. © 2014 Wiley Periodicals, Inc.     

Electronic processes in NO dimerization on Ag and Cu clusters: DFT and MRMP2 studies

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag₂ and Cu₂ clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag₂ and Cu₂ unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag₂ and Cu₂ to NO moieties plays important role in N N bond formation between two NO molecules. This CT considerably decreases nondynamical correlation effect. Also, the DFT method could be applied to this NO dimerization, if appropriate DFT functional is used; all pure functionals examined here and most of the hybrid functionals underestimated the activation barrier (E_a), while only ωB97X provided E_a similar to CCSD(T)-calculated value. NO dimerization on similar Cu₂ and Cu₅ needs moderately larger E_a than those on Ag₂ and Ag₅, because frontier orbital participating in the CT exists at lower energy in Cu₂ and Cu₅ than in Ag₂ and Ag₅. The E_a decreases in the order Ag₂ >> Ag₃₈ > Ag₇ ∼ Ag₅ and the reaction energy (ΔE) is positive (endothermic) in Ag₂ but significantly negative in Ag₃₈, Ag₇, and Ag₅, indicating that various Ag clusters could be effective for NO dimerization except for Ag₂. The decreasing order of E_a and increasing order of exothermicity are attributed to increasing order of the frontier orbital energy of Ag₂ < Ag₃₈ < Ag₇ ∼ Ag₅. © 2018 Wiley Periodicals, Inc.     

DFT and MO calculations of atomic and molecular chemisorption energies on surface cluster models

Summary Density functional theory (DFT) (including gradient corrections) and MCPF calculations have been performed for atomic (H, C, N, O) and molecular CH _x (x = 1–3) chemisorption on cluster models of different sites of the Cu(100) surface. The DFT and MCPF results are in good agreement once the important effects of core-valence correlation have been accounted for in the MCPF calculations by including contributions from a core polarization potential (CPP); in the DFT approach the core-valence correlation is obtained directly from the total density using the functional. Very large effects on the four-fold hollow site binding energy from core-valence correlation are found for C, N and CH. Several different DFT functionals were employed and compared in the calculations.     

Smoothing techniques of global optimization: Distance scaling method in searches for most stable Lennard–Jones atomic clusters

Spatial averaging of the potential energy function facilitates the search for the most stable configuration of a molecular system. Recently some global optimization methods of this kind have been designed in the literature that rely on physical phenomena such as diffusion, wave function evolution in quantum mechanics, Smoluchowski dynamics, evolution in temperature of canonical ensembles, etc. In the present article we highlight the fact that all these methods, when applied to the Gaussian distributions of an ensemble, represent special cases of a set of differential equations involving the spatially averaged potential energy. Their structure suggests that the nature's strategy to cope with the global optimization is robust and differs only in the details in particular applications. The strategy consists of going downhill of the averaged potential energy, removing the barriers, and hunting for low energy regions by a selective increasing of the spatial averaging. In this study we explore the deformation of the potential rather than its averaging. The deformation comes from scaling of atomic distances and reduces the barriers even more effectively than the Gaussian averaging. The position and widths of the Gaussian distribution evolve similarly to the Gaussian density annealing (GDA), but we allow elliptical instead of spherical Gaussians as well as branching of the single trajectory of the system into multiple ones. When the temperature reaches 0 K, one has a number of independent Gaussian distributions, each corresponding to a structure and (usually low) energy of the system. The multiple elliptic-Gaussian distance scaling method has been applied to clusters of argon atoms (N=5,…,31), a system serving usually as a benchmark domain. The method found the global minima for all but three clusters (of very low energy). The procedure is 20 or more times less expensive than the GDA one. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 2040–2049, 1997     

A conformational analysis method for understanding the energy landscapes of clusters.

A newly developed unbiased structural optimization method, named dynamic lattice searching (DLS), is proposed as an approach for conformational analysis of atomic/molecular clusters and used in understanding the energy landscape of large clusters. The structures of clusters are described in terms of the number of basic tetrahedron (BT) units they contain. We found that the hit numbers of different structural motifs in DLS runs is proportional to the number of BTs. A parameter T(max) is defined to limit the maximal number of atoms moved in a structural transition. Results show that T(max) is a key parameter for modulating the efficiency of the DLS method and has a great influence on the hit number of different motifs in DLS runs. Finally, the effect of potential range on the conformational distribution of the (Morse)(98) cluster is also discussed with different potential-range parameters.     

DFT cluster model of hydroperoxide activation intermediates in Ti-containing porous silicates

Various intermediates of hydroperoxide activation on Ti-containing microporous and mesoporous silicates were studied using the DFT cluster model approach. Lowering the coordination number of Ti(IV) ions in the matrix was found to destabilize the peroxide form =Ti(OO) and to hinder the formation of singlet dioxygen.     

Synthesis and structural characterization of a new trimetallic thiocubane cluster

The trimetallic cluster W2CuAgS4(TDT)2(PPh3)2-CH2Cl2 (TDT= [S2(C6H3)CH3]2-) (2) has been prepared from the reaction of the well-defined molecule building block [W2S4(TDT)2]2-(1) with AgNO3,CuBr and PPh3.The structure contains a [W2CuAgS4]4+ distorted cubane-like core.Two types of metal-metal bonds exist in the core.One is W-W bond of which length is 0.2871(1) nm,the other is W-M' (M'=Cu or Ag) bonds,whose mean distance is 0.2980 nm.The details of synthesis,structure,IR,UV-Vis and 31P NMR spectra are reported.The crystallographic data are:space group F21/n,with 0=1.6987(4),6=1.7763(6),c=1.8918(5) nm,β=98.54(2)°,V=5.645(3) nm3,Z=4,and final R=0.043 for 6437 observed reflections.