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.     

Structural,spectroscopic aspects,and electronic properties of (TiO2)n clusters: A study based on the use of natural algorithms in association with quantum chemical methods

In this article, we propose a stochastic search‐based method, namely genetic algorithm (GA) and simulated annealing (SA) in conjunction with density functional theory (DFT) to evaluate global and local minimum structures of (TiO₂)_n clusters with n = 1–12. Once the structures are established, we evaluate the infrared spectroscopic modes, cluster formation energy, vertical excitation energy, vertical ionization potential, vertical electron affinity, highest occupied molecular orbital (HOMO)‐lowest unoccupied molecular orbital (LUMO) gaps, and so forth. We show that an initial determination of structure using stochastic techniques (GA/SA), also popularly known as natural algorithms as their working principle mimics certain natural processes, and following it up with density functional calculations lead to high‐quality structures for these systems. We have shown that the clusters tend to form three‐dimensional networks. We compare our results with the available experimental and theoretical results. The results obtained from SA/GA‐DFT technique agree well with available theoretical and experimental data of literature. © 2013 Wiley Periodicals, Inc.     

A detailed analysis of pseudorotation in PH4F

Summary Pentacoordinated molecules are thought to undergo intramolecular isomerization by the widely accepted Berry pseudorotation mechanism. Through our investigations, we have found that the actual pseudorotation for the PH₄F system is more complex than that envisioned by Berry. The potential energy surface of PH₄F is mapped out at the RHF/6-311G(d, p) level. According to the Berry mechanism, this system is expected to have two minima and two maxima; however, the system actually has two transition states and one global minimum. The minimum energy path from the highest transition state is followed to the second transition state, which in turn has a minimum energy path leading to the global minimum. Along the path between the two transition states there is a branching region. This portion of the potential energy surface is probed extensively.Dedicated to Prof. Klaus Ruedenberg     

Molecular mechanics conformational analysis of cyclononane using the RIPS method and comparison with quantum-mechanical calculations

The recently reported Random Incremental Pulse Search (RIPS) technique has been used to probe the conformational energy surface of cyclononane. The stochastic method permits searching of the potential energy surface for all minimum-energy conformations. The search located all previously reported structures together with three additional conformations that were not found by earlier, primitive searching techniques. Two of these structures are high-nergy skew forms, and the third is a low-energy conformer that should contribute significantly to the overall equilibrium set of cyclononane conformations. The global minimum has been found to be the D₃ symmetrical twist chair-boat (TBC) form in accordance with previous studies. The newly discovered low-energy structure, which lies only 2.2 kcal/mol above the global minimum, has been designated twist chair-twist chair (TCTC). The two higher energy conformers are skewed chair-chair (SCC) and skewed boat-boat (SBB) forms that are 5.7 kcal/mol and 10.4 kcal/mol above the global minimum, respectively. The seven reported conformations were reanalyzed quantum mechanically (AM 1), and a comparison between MM 2 and AM 1 results is presented.     

Theoretical study of potential energy surface and vibrational spectra of ArF2 system

Anab initio potential energy surface (PES) of ArF₂ system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm^-1 atR = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm^-1 atR = 0.3486 nm. A saddle point is found atR = 0.3486 and τ = 61° with the well depth of -61.53 cm^-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration.     

Exploring the first-shell and second-shell structures arising in the microsolvation of Li+ by rare gases

An evolutionary algorithm was used to search for the low-energy structures of Li⁺Ar_n and Li⁺Kr_n (n = 1 − 14). Two functions were used to describe the interaction potential at the CCSD(T)/aug-cc-pVQZ level of theory: one is based on a sum of all pair potentials, whereas the other includes three-body interactions. In general, the global minimum structures are similar for both Li⁺Ar_n and Li⁺Kr_n. Modifications in the octahedral structure of the first solvation shell lead to a high-energy penalty. Conversely, the second solvation shell shows a panoply of minima with similar energies that are likely to be interconverted. Post-optimization at the MP2 level confirmed that, for n = 2 and 3, one has to include three-body terms in the potential to reproduce the low-energy structures. Additionally, MP2 calculations indicate that energy reorder of the global minimum structure observed for Li⁺Kr₈ is related to the Kr₃ Axilrod-Teller-Muto term included in the potential.     

A density functional theory study of the Cu+·(CO)n (n = 1–3) complexes

Density functional theory calculations, with an effective core potential for the copper ion, and large polarized basis set functions have been used to construct the potential energy surface of the Cu⁺·(CO)_n (n = 1–3) complexes. A linear configuration is obtained for the global minimum of the Cu⁺·CO and Cu⁺·(CO)₂ complexes with a bond dissociation energy (BDE) of 35.9 and 40.0 kcal mol^-1, respectively. For the Cu⁺·(CO)₃ complex, a trigonal planar geometry is obtained for the global minimum with a BDE of 16.5 kcal mol^?1. C-coordinated copper ion complexes exhibit stronger binding energy than O-coordinated complexes as a result of C_lp → 4s σ-donation. The computed sequential BDEs of Cu⁺·(CO)_n (n = 1–4) complexes agree well with experimental findings, in which the electrostatic energy and σ-donation play an important role in the observed trend.     

A Fukui function‐guided genetic algorithm. Assessment on structural prediction of Sin (n = 12–20) clusters

Theoretical studies are essential for the structural characterization of clusters, when it comes to rationalize their unique size‐dependent properties and composition. However, the rapid growth of local minima on the potential energy surface (PES), with respect to cluster size, makes the candidate identification a challenging undertaking. In this article, we introduce a hybrid strategy to explore the PES of clusters. This proposal involves the use of a biased initial population of a genetic algorithm procedure. Each individual in this population is built by assembling small fragments, according to the best matching of the Fukui function. The performance of a genetic algorithm procedure. The performance of the method is assessed on the PES exploration of medium‐sized Si_n clusters (n = 12–20). The most relevant results are: (a) the method converges at almost half of the time used by the canonical version of the GA and, (b) in all the studied cases, with the exception of Si₁₃ and Si₁₆, the method allowed to identify the global minimum (GM) and other important low‐lying structures. Additionally, the apparent deficiency of the proposal to identify the GM was corrected when a Si atom, or other low‐lying isomers, were considered to build the clusters. © 2017 Wiley Periodicals, Inc.     

Theoretical prediction for the structures of gas phase lithium oxide clusters: (Li2O)n (n = 1–8)

We apply genetic algorithm combining directly with density functional method to search the potential energy surface of lithium‐oxide clusters (Li₂O)_n up to n = 8. In (Li₂O)_n (n = 1–8) clusters, the planar structures are found to be global minimum up to n = 2, and the global minimum structures are all three‐dimensional at n ≥ 3. At n ≥ 4, the tetrahedral unit (TU) is found in most of the stable structures. In the TU, the central Li is bonded with four O atoms in sp³ interactions, which leads to unusual charge transformation, and the probability of the central Li participating in the bonding is higher by adaptive natural density partitioning analysis, so the central Li is in particularly low positive charge. At large cluster size, distortion of structures is viewed, which breaks the symmetry and may make energy higher. The global minimum structures of (Li₂O)₂, (Li₂O)₆, and (Li₂O)₇ clusters are the most stable magic numbers, where the first one is planar and the later both have stable structural units of tetrahedral and C_4v. © 2012 Wiley Periodicals, Inc.     

Thermal expansion of polymers submitted to supercritical CO2 as a function of pressure

Interactions of polymers with compressed supercritical CO₂ has been studied by using pressure‐controlled scanning calorimetry (PCSC). Global cubic thermal expansion coefficients (α_{pol‐g‐int}) for medium density polyethylene (MDPE) and poly(vinylidene fluoride) (PVDF) saturated with supercritical CO₂ have been determined at 352.4 K over the pressure range from 0.1 MPa to 100 MPa. In both cases, the isotherms of global α_{pol‐g‐int} exhibit minima near 20 MPa. At pressures below the minimum, α_{pol‐g‐int} for the PVDF–CO₂ system are higher than for the MDPE–CO₂ system, while at pressures above the minimum the opposite was observed. This proves that incorporation of CO₂ in PVDF is stronger than in MDPE. The appearance of the minimum is attributed to the action of compressed CO₂ molecules, which at higher pressures are forced to enter deep inside the interstitial or other voids in the polymer and cause their mechanical distension, which must be associated with an endothermic effect. The measurements have been performed on polymers used for fabrication of pipelines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:185–194, 2006     

Structure,spectroscopy and electronic properties of neutral lattice-like (MgO) n clusters: a study based on a blending of DFT with stochastic algorithms inspired by natural processes

In this article, we explore the feasibility of using stochastic optimization techniques, which are inspired by natural processes, namely simulated annealing (SA) and genetic algorithm (GA) in association with DFT, to find out the global minimum structures of (MgO) _n clusters with n being in the range of 2–15. To check whether the structures are indeed the correct ones, we proceed to do several property calculations like IR-spectroscopic modes, vertical excitation energy, cluster-formation energy, vertical ionization potential, the HOMO–LUMO gap as well as polarizability and hyperpolarizability—both static and dynamic. We emphasize on the point that an initial determination of structure using SA/GA leads to very quick relaxation to structures which are very close to the structures predicted from quantum chemical calculations done from the outsets like DFT. The general pattern of these systems to form beautiful three-dimensional lattice networks is also evident from our study.     

High-level ab initio calculations on CH+2(2A1) + PO(2II) reactions

We present ab initio calculations carried out in the framework of the G 2 theory on the singlet and triplet potential energy surfaces corresponding to the gas-phase between CH⁺₂ and PO. The global minimum of both potential energy surfaces is a cyclic singlet-state cation. Oxygen attachment of PO to CH⁺₂ in a triplet configuration is accompanied by a P(SINGLEBOND)O bond fission, with the result that the corresponding global minimum is an ion-dipole complex between P⁺(³P) and formaldehyde. This is also consistent with the fact that our results predict the formation of formaldehyde to be highly exothermic, either as a neutral or as radical cation. Both charge-transfer processes yielding CH₂(³B₁) or CH₂(¹A₁) are also exothermic. The formation of other carbon and oxygen containing species are endothermic. © 1996 John Wiley & Sons, Inc.     

New Observations on the Belousov-Zhabotinskii Reaction. The Oscillating Reaction of Organic Gallic Acid and Potassium Bromate Catalyzed by 1,10-o-Phenanthroline-Iron(II) Complex

The oscillating reaction involving organic gallic acid (GA), potassium bromate, and a metal ion complex has been reinvestigated. In contrast to other previous reports, this oscillating reaction is catalyzed by the [Fe(phen)_n]²⁺ ion (phen = 1,10-o-phenanthroline, n=1, 2, 3) rather than by the cerium ion. The characteristics of the oscillations depend on the temperature and on the concentrations of the potassium bromate, gallic acid, [Fe(phen)_n]²⁺, and sulfuric acid. A cyclic voltammetric study indicates that the redox potential and the reversibility of the [Fe(phen)_n]^2+/3+ couple play a major role in catalyzing this oscillating system.     

Si6C18: A bispentalene derivative with two planar tetracoordinate carbons

Here we show that substituting the ten protons in the dianion of a bispentalene derivative (C₁₈H₁₀²⁻) by six Si²⁺ dications produces a minimum energy structure with two planar tetracoordinate carbons (ptC). In Si₆C₁₈, the ptCs are embedded in the terminal C₅ pentagonal rings and participate in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Our exploration of the potential energy surface identifies a triphenylene derivative as the putative global minimum. Nevertheless, robustness to Born–Oppenheimer molecular dynamics (BOMD) simulations at 900 and 1500 K supports bispentalene derivative kinetic stability. Chemical bonding analysis reveals ten delocalized π-bonds, which, according to Hückel's 4n + 2 π-electron rule, would classify it as an aromatic system. Magnetically induced current density analysis reveals the presence of intense local paratropic currents and a weakly global diatropic current, the latter agreeing with the possible global aromatic character of this specie.     

Acetylcholine in water: Ab-initio potential and Monte Carlo simulation

Ab initio SCF-LCAO-MO computations using a minimal basis set have been carried out on the acetylcholine ion in different conformations. The rotational barrier around the C9-C8-O1-C2 dihedral angle (τ₁) has been also calculated: the curve presents a broad minimum. SCF calculations have been carried out on the system Ach-water at 468 different separations and/or orientations; the interaction energies were then fitted to a pair potential function used in Monte Carlo (MC) simulations of Ach water solution. The rdfs indicate a global first hydration shell with about 38 waters. Details about the hydration shell are presented. The overall MC results indicate that for the Ach ion in water solution at room temperature relative free rotation is possible around τ₁, and that Ach is well represented as a large positively charged hydrated globe with a small mobile tail free of strong interactions with the surrounding water molecules.     

A detailed investigation on the global minimum structures of mixed rare‐gas clusters: Geometry,energetics, and site occupancy

We performed a global minimum search of mixed rare‐gas clusters by applying an evolutionary algorithm (EA), which was recently proposed for binary atomic systems (Marques and Pereira, Chem. Phys. Lett. 2010, 485, 211). Before being applied to the potentials used in this work, the EA was further tested against results previously reported for the Ar_NXe_38?N clusters and several new putative global minima were discovered. We employed either simple Lennard‐Jones (LJ) potentials or more realistic functions to describe pair interactions in Ar_NKr_38?N, Ar_NXe_38?N, and Kr_NXe_38?N clusters. The long‐range tail of the pair‐potentials shows some influence on the energetic features and shape of the structure of clusters. In turn, core–shell type structures are mostly observed for global minima of the binary rare‐gas clusters, for both accurate and LJ potentials. However, the long‐range tail of the potential may have influence on the type of atoms that segregate on the surface or form the core of the cluster. While relevant differences for the preferential site occupancy occur between the two potentials for Ar_NKr_38?N (for N > 21), the type of atoms that segregate on the surface for Ar_NXe_38?N and Kr_NXe_38?N clusters is unaffected by the accuracy of the long‐range part of the interaction in almost all cases. Moreover, the global minimum search for model‐potentials in binary systems reveals that the surface‐site occupancy is mainly determined by the combination of two parameters: the size ratio of the two types of particles forming the cluster and the minimum‐energy ratio corresponding to the pair‐interactions between unlike atoms. © 2012 Wiley Periodicals, Inc.     

Quantum-Chemical Study of the Adducts of Silicon Halides with Nitrogen-containing Donors: II.1 Calculation of a Donor-Acceptor Bond Energy. Complex trans-SiH4·2NH3

Structural and thermodynamic characteristics of the trans-SiH₄·2NH₃ adduct were obtained by ab initio and DFT (RHF and B3LYP) calculations. Scanning the potential energy surface (PES) of the com plex showed that its structure corresponds to a local minimum, whereas the global minimum corresponds to the free fragments. The energy of the silicon-nitrogen chemical bond was calculated with inclusion of fragment rearrangement energies and basis set superposition error. The procedure offered for calculating the Si-N bond energy was extended to adducts of silicon halides with ammonia. It was found that the energy of SiX₄ rearrangement contributes most to the energies of donor-acceptor bonds in mono- and diammoniates of silicon tetrahalides.     

Global optimization of atomic and molecular clusters using the space-fixed modified genetic algorithm method

A modified genetic algorithm approach has been applied to atomic Ar clusters and molecular water clusters up to (H₂O)₁₃. Several genetic operators are discussed which are suitable for real-valued space-fixed atomic coordinates and Euler angles. The performance of these operators has been systematically investigated. For atomic systems, it is found that a mix of operators containing a coordinate-averaging operator is optimal. For angular coordinates, the situation is less clear. It appears that inversion and two-point crossover operators are the best choice. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1233–1244     

Synthesis and Anti‐tumor Evaluation of Novel C‐37 Modified Derivatives of Gambogic Acid

Gambogic acid (GA, 1 ), the most prominent representative of Garcinia natural products, has been reported to be a promising anti‐tumor agent. In order to further explore the structure‐activity relationship of GA and discover novel GA derivatives as anti‐tumor agents, 17 novel C‐37 modified derivatives of GA were synthesized and evaluated for their in vitro anti‐tumor activities against A549, HCT‐116, BGC‐823, HepG2 and MCF‐7 cancer cell lines. Among them, 11 compounds were found to be more potent than GA against some cancer cell lines. Notably, compound 8 was almost 5–10 folds more active than GA against A549 and BGC‐823 cell lines with the IC₅₀ values of 0.12 µmol·L^?1 and 0.57 µmol·L^?1, respectively. Chemical modification at C‐37 position of GA by introducing of hydrophilic amines could lead to increased activity and improved drug‐like properties. These findings will enhance our understanding of the structure‐activity relationship (SAR) of GA and lead to the discovery of novel GA derivatives as potential anti‐tumor agents.