Theoretical study of polymerization of pyrrole

The polymerization process of pyrrole has been theoretically studied using the semiempirical molecular orbital (MO) method. As a model for the polymerization, particularly representing the initial-stage reaction near the anode of the electropolymerization system, the dimerization of pyrrole is examined by the process of coupling of two cationic monomer radicals in two specifically different ways, i.e., via the σ-radical or via the π-radical. Furthermore, some related calculations are undertaken in connection with the reactions between cationic monomer and dimer radicals, and between a neutral monomer and a cationic monomer radical.     

TOTAL ENERGIES AND ELECTRONIC STRUCTURES OF CO_3Ti AND HYDROGENIZED Co_3Ti

1.IntroductionAgreatdealofinteresthasbeenshowninL12typeintermetalliccompoundSandalloyssincetheyshowasubstantialincreaseinflowstresswithincreasingtemperature[1--3].However,thebrittlenessofthistypeofalloyhaspreventeditfrombeingusedasanalloybaseforastructuralmaterial.TakasugiandI...i[4]hadfoundCo3Ticompoundtohaveintrinsicallygoodductilityatawidetemperaturerange.TheyhadinvestigatedtheinfluenceofahydrogenenvironmentORthemechanicalpropertiesofL12typeCo3Ticompoundandemphasizedthathydrogenembrittl…     

Ab initio MO–CI based quantum master equation approach: Exciton dynamics of weakly and strongly coupled J-type aggregates

In order to investigate the time evolutions of electron and hole distributions in weakly and strongly coupled H₂ dimer models, we employ a novel dynamic exciton expression derived from the exciton density matrices calculated by the quantum master equation combined with the ab initio molecular orbital (MO)–configuration interaction (CI) method. The oscillation of exciton distribution over the monomers is observed in case of small inter-monomer distance, where the coupled dipole approximation is invalid. The result originates in the covalent character of inter-monomer interaction in the first excited state, i.e., delocalized character of LUMO distribution.     

Theoretical study of corrosion inhibition of amides and thiosemicarbazones

An examination of quantum chemical and corrosion inhibition studies were carried out to investigate whether any clear links exist between the results of quantum chemical calculations and the experimental efficiencies of urea (U), thiourea (TU), acetamide (A), thioacetamide (TA), semicarbazide (SC), thiosemicarbazide (TSC), methoxybenzaldehydethiosemicarbazone (MBTSC), 2-acetylpyridine-(4phenyl) thiosemicarbazone (2AP4PTSC), 2-acetylpyridine-(4-methyl) thiosemicarbazone (2AP4MTSC), benzointhiosemicarbazone (BZOTSC) and benzilthiosemicarbazone (BZITSC) being corrosion inhibitors. The quantum chemical calculations have been performed by using DFT, ab-initio molecular orbital and semi-empirical methods for some amides and thiosemicarbozone derivatives being corrosion inhibitors. The highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital energy (E_LUMO), the energy gap between E_HOMO and E_LUMO (ΔE_HOMO-LUMO), dipole moments (μ), charges on the C, O, N, S atoms, the total energies of the molecules and the polarizabilities 〈α〉, the coefficients of the development of the MO over the atomic orbital (AO) corresponding to the between atoms which a new bond is established have been calculated.The results of quantum chemical calculations and experimental efficiencies of inhibitors were subjected to correlation analysis. We have reached the conclusion that the synthesis of better corrosion inhibitors can be achieved by controlling all electronic properties and parameters of a selected group of molecules.     

Collectorless flotation of marmatite with pine oil

The interaction between pine oil and marmatite without collectors and activators was investigated by flotation,scanning electron microscope and energy-dispersive spectrometer(SEM-EDS),infrared(IR) spectroscopy,Zeta potential,and first-principle theory calculations.The flotation results show that marmatite exhibits considerable floatability with the addition of pine oil.SEM-EDS results show that carbon atomic ratios on the surface are significantly high,which suggests that the flotation of marmatite is caused by the adsorption of pine oil.Further evidence of the adsorption mechanism was given by IR,and Zeta potential examining pine oil depends on the physical adsorption on the surface independently.The first-principle theory calculations indicate that pine oil molecule adsorbs on Zn and Fe atom surfaces by ionic bond and covalent bond of adsorption energies of-1.23and-1.51 eV,respectively.P orbital of O atom,s orbital of Zn atom,and d orbital of Fe are the major participants.     

Catalysis by Gold Nanoparticles

Gold catalysts have superior activity in CO and other oxidations at low temperatures. Both a small (~ 5nm) particle size and the presence of a partly reducible oxide (ceria or a transition metal oxide) have a beneficial effect on the catalyst performance. The present paper reviews our recent studies focused on understanding the specific role of the Au particle size and that of the oxide (MO). Our personal viewpoint on gold catalysis is outlined. The effects of Au particle size and of the oxidic additive are distinguished by using several alumina-supported gold catalysts having different gold particle sizes and various oxidic additives. The most active catalyst in CO oxidation is the multicomponent catalyst Au/MgO/MnOx/Al2O3 with MgO being a stabilizer for the Au particle size and MnOx being the cocatalyst. This catalyst also exhibits good performance in selective oxidation of CO in a hydrogen atmosphere, a reaction relevant for the development of polymer electrolyte fuel cell technology.     

Density functional theory study on hydrogenation mechanism in catalyst-activated Mg（0001） surface

A small amount of Fe3O4 catalyst is known to substantially improve the adsorption and desorption thermodynamics and kinetics of Mg-based materials. Using density functional theory in combination with nudged elastic band method, the dissociative chemisorptions of hydrogen on both pure and Fe-doped Mg(0001) surfaces were studied. The adsorption energy calculations show that a weakly physisorbed state above pure and Fe-doped Mg surface atoms can serve as a precursor state to dissociative chemisorption. Then, the dissociation pathway of H2 and the relative barrier were investigated. The calculated dissociation barrier (1.08 eV) of hydrogen molecule on a pure Mg(0001) surface is in good agreement with comparable experimental and theoretical studies. For the Fe-doped Mg(0001) surface, the activated barrier decreases to 0.101 eV due to the strong interaction between the s orbital of H and the d orbital of Fe.     

Intrinsic reactivity of gold nanoparticles: Classical, semi-empirical and DFT studies

Gold nanoparticles used in most experiments (1–10 nm) in gold catalysis show varying degrees of reactivity, with particles below 5 nm generally being more reactive. The origin of this activity is a subject of a number of model experiments and theoretical studies on either clusters of a few atoms in size or extended surfaces (smooth or stepped). In the work described here, a classical theory for the variation of the metal workfunction with cluster size, Extended Hückel Theory (EHT) calculations combined with DFT calculations, as well as a carbon monoxide (CO) chemisorption model are combined to develop a relationship between metal particle size and the particle's reactivity towards CO. For gold, it is shown that while the contribution of the d-band hybridization energy to the total CO chemisorption energy is unfavourable for bulk gold, this is not true for gold particles below 5–6 nm. That is, the d-band hybridization energy is negative for small gold particles. This is believed to be explanation of the onset of high reactivity for small gold particles.     

Phase-field theory of grain growth in the presence of mobile second-phase particles

We have developed a phase-field model for grain growth in the presence of mobile second-phase particles. In this model, each grain and particle is represented by a unique order parameter. The grain boundaries sweep the mobile particles during grain growth. The particle velocity is taken to be proportional to the driving force arising from the curvature of the phase boundary in the neighborhood of the particle. The proportionality factor is the constitutive parameter representing the mobility of the particle. We first study the model in a one-dimensional axisymmetric setting and compare the results with theoretical calculations. We then study the interaction of a bicrystal grain boundary with a dilute distribution of particles. Finally we show the effect of particles on polycrystalline grain growth.     

Quantum chemical studies on corrosion inhibition of some lactones on mild steel in acid media

Study of the efficacy of some lactones to counter iron corrosion in 1 M hydrochloric acid using ab initio quantum chemical deductions and its comparison with the available experimental data forms a part of this research. It is believed that the inhibition efficiency has lucid correlation with the charge of oxygen atoms of inhibitor molecules. Furthermore, thermo-chemical calculations for oxepan-2-one (L3) on iron cluster result in adsorption energies close to experimental values. However, the interaction energies of L3 and iron cluster with the natural bond orbital are also reported. Furthermore, interaction energy of hydrogen ion and inhibitor with iron surface is investigated.     

O2在NiTi合金(100)表面吸附的理论研究

采用密度泛函方法应用赝势基组对NiTi合金（100）表面的电子结构以及氧分子（O2）的吸附和解离过程进行了系统研究．结果表明,Ti原子裸露表面比Ni原子裸露表面反应活性高,02吸附为活化解离吸附,顶位吸附结构最不稳定,易向桥位或洞位吸附转化,桥位吸附对应的吸附结构最为稳定．态密度分析和结构分析表明,氧原子与表面的相互作用主要是由氧原子价轨道和NiTi合金杂化表面轨道贡献．     

Charge transport in DNA strands using fragment orbital theory

A semi-empirical Valence-Bond/Hartree–Fock (VB/HF) method is developed to calculate one- and two-electron interactions between molecular fragments in conducting supramolecular stacks. This fragment orbital-based formalism allows for the consistent extraction of an effective hamiltonian defined as a “frontier orbital” model. This hamiltonian quantitatively describes transfer and electrostatic interactions between conducting electrons while reducing the active space so dramatically that the electronic eigenstates of very large systems may be investigated. The VB/HF formalism is applied here to the derivation an effective model for conduction holes along doped DNA double strands. Transferable intra and intersite parameters are first evaluated from VB/HF calculations carried out on nucleoside pairs. From this interaction databank, the effective hamiltonian of any kind of nucleoside sequence can eventually be defined. The thermalized charge distribution for a single hole delocalized along DNA sequences is then calculated and compared to the experimental yields of damage revealed by photocleavage experiments.     

Electronic structure of polyiminovinylene as a tractable model for polyaniline

The electronic structures of polyiminovinylene (PIV) as well as polyaniline (PAn) are studied theoretically using the one-dimensional tight-binding self consistent field-crystal orbital (SCF-CO) method. PIV was employed as a tractable model for PAn to inspect the electronic process when the redox states of PAn are changed. The conduction mechanism caused by partial protonation (oxidation) is discussed and the possibility of the formation of bipolaron in the partially protonated polymer skeleton is examined.     

CHARACTERISTICS OF METAL-HYDROGEN INTERACTION IN HYDROGEN STORAGE ALLOYS

1.IntroductiollAdvancedenergyconversionmaterialshavebeeningreatdemandforthedevelopmentoffuturecleanenergysystems.Inparticular,hydrogenstoragealloywithhighhydrogencapacityisveryimportantforthepracticaluseofcleanhydrogenenergy.Recently,wehaveinvestigatedthealloyingeffectsontheelectronicstructuresoftypicalhydrogenstoragealloys,LaNi,['],ZrMn,['],TiFe[3],Mg,Ni[4]andbccV[5].Itisfoundthathydrogeninteractmorestronglywithhydridenon--formingelements,B,thanhydrideformingelements,A,ineveryhydrogensto…     

Experimental and theoretical study of organic corrosion inhibitors on iron in acidic medium

The corrosion inhibition on metallic iron surfaces by organic molecules has been investigated both experimentally and theoretically. The inhibition efficiency of thiophenol, phenol and aniline have been compared through gravimetric and electrochemical experiments. From EH–MO and EH-tight-binding calculations, it has been possible to compare the strength of the bonding interaction between the inhibitors and the metal, with and without the presence of adsorbed protons on the metal surface, and to provide a rationalization of their different efficiencies.     

A novel fluorescent,conducting polymer: Poly[1-(thiophene-2-yl)benzothieno[3,2-b]benzothiophene] electrosynthesis,characterization and optical properties

Poly[1-(thiophene-2-yl)benzothieno[3,2-b]benzothiophene] (poly-TBTBT) was electrosynthesized on a Pt electrode by anodic oxidation of TBTBT in 0.1 M LiClO₄ acetonitrile solution and in a micellar medium (water/methanol, 9/91, v/v) containing 0.39 M perchloric acid and 0.1 M sodium dodecylsulfate (SDS). Films prepared in acetonitrile were thick and electroactive, whereas in micellar medium they were very thin. Poly-TBTBT was characterized by cyclic voltammetry, MALDI-TOF mass spectrometry, IR, and scanning electron microscopy (SEM). Poly-TBTBT films were essentially constituted of short-chain oligomers (dimer to octamer). The molecular orbital (MO) calculations, carried out on the basis of a radical–cation electropolymerization mechanism, confirmed the spectral results The optical properties, including the electronic absorption and fluorescence spectra, were also examined.     

Transition metal alloying effects on chemical bonding in TiH2

By use of the linear-combination-of-atomic-orbital (LCAO) method for a cluster model, we study the alloying effect on chemical bonding in TiH₂ systems. In order to verify that the cluster model is suitable for describing the crystal behavior, the electronic structures in pure dihydrides, such as ScH₂, TiH₂, VH₂, YH₂, ZrH₂ and NbH₂ are calculated. Good agreement of the variant trend of the metal–hydrogen interaction with that of the enthalpy of formation for each pure dihydride is found, and the ionic and covalent contributions to the metal–hydrogen interaction are evaluated quantitatively as a reference for judging their contributions in the alloyed TiH₂. The alloying effect on the ionic interaction of alloyed TiH₂ is somewhat weaker than that on the covalent interaction. It is found that hydrogen makes a stronger covalent bond with the weaker hydride forming elements and hydride non-forming elements rather than the stronger hydride forming elements if there exist Ti atoms in the neighborhood in the alloyed TiH₂. This trend can be understood by the orbital bonding analysis. The energy interval and orbital overlap contributions to the interaction between metal and hydrogen atoms are discussed qualitatively.     

Synergistic Effect of Alloying Atoms on Intrinsic Stacking-Fault Energy in Austenitic Steels

Intrinsic stacking-fault energy is a critical parameter influencing the various mechanical performances of austenitic steels with high Mn concentrations.However,quantitative calculations of the stacking-fault energy(SFE) of the face-centered cubic(fcc) Fe,including the changes in concentrations and geometrical distribution of alloying atoms,cannot be obtained by using previous computation models.On the basis of the interaction energy model,we evaluated the effects of a single alloying atom(i.e.,Mn,Al,Si,C and N),as well as its aggregates,including the Mn-X dimer and Mn_2-X trimer(X = Al,Si,C and N) on the SFE of the fcc Fe via first-principle calculations.Given low concentrations(10 wt%) of alloying atoms,dimers and trimers,theoretical calculations reveal the following:(1) Alloying atom Mn causes a decrease in the SFE,whereas Al,Si,C and N significantly increase the SFE;(2) combination with other alloying atoms to form the Mn-X dimer(X = Al,Si,C and N) exerts an effect on SFE that,to a certain extent,is close to that of the corresponding single X atom;(3) the interaction between Mn_2-X and the stacking fault is stronger than that of the corresponding single X atom,inducing a significant increase in the SFE of fcc Fe.The theoretical results we obtained demonstrate that the increase in SFE in high-Mn steel originates from the synergistic effect of Mn and other trace alloy atoms.     

A theoretical study of the electronic properties of intercalated graphite

We present the results of electronic structure calculations for first and second stages of lithium intercalated graphite (LiC₆ and LiC₁₂). The various stages of Li intercalated graphite all have hexagonal symmetry, where different carbon layers are stacked with C-atoms directly on top of each other (AIAI…), as opposed to natural graphite where the C-layers are staggered (ABAB…). All our calculations have been performed within the framework of the extended tight binding method with Gaussian type basis sets. From the orbital and total densities of states, we conclude that Li-2s electrons are transferred into carbon π-bands. This results in shifting the Fermi level into the region of high density of states (compared with pure graphite) and, hence, to observed metallic behavior. The calculated density of states for LiC₆ and LiC₁₂ is 0.25 and 0.12/(eV C-atom), respectively. Recall that for pure graphite the value is nearly zero and for copper it is 0.29. We also found it instructive to obtain the electronic structure of LiC₆ and LiC₁₂ based on a rigid band model.     

Investigation on poly(vinylene sulphide): Ab initio energy band structure,use of effective core potentials,lattice sum truncation

The energy band structures of two structural isomers of poly(vinylene sulphide) are calculated using the ab initio Hartree-Fock crystal orbital method. The basis set dependence and the convergence of quantities like the total energy per elementary cell and the atomic electron population with the number of interactions with neighbours are investigated. The band structure calculations are repeated employing effective core potentials first for sulphur atoms only and then for all non-hydrogen atoms. The results of the valence-electron only and the mixed computations agree very well with the all-electron calculations. A lattice sum truncation scheme, based on symmetric and electrostatically-balanced cut-off radii, is investigated. It turns out that the convergence of the total energy per elementary cell is very slow using these cut-off schemes, whereas the electronic and energetic properties rapidly converge in the strict interaction with neighbours approximation. Part of the explanation is found in the incorrect treatment of the nuclear-nuclear repulsion terms, and the inconsistent handling of the electron-nuclear repulsion integrals.