Ab Initio and Density Functional Study on the First Hyperpolarizabilities of Squaric Acid Homologues

The first hyperpolarizabilities of four squaric acid homologues: squaric acid, 1,2-dithiosquaric acid,1,2-diselenosquaric acid and 1,2-ditellurosquaric acid have been calculated using ab initio and DFT methods. The effects of equilibrium geometries, basis set and electron correlation on the first hyperpolarizabilties of these molecules were investigated. The frequency dispersion effect and solvent effect, which are essential to get reliable outputs in comparison to the experimental results, have also been explored. On the basis of these investigations, it is worthy to point out that the heavy atom effect takes effect for these squaric acid homologues.     

A Density Functional Theory Study on the Adsorption of CN on Ni(111) Surface

1 INTRODUCTION Cyanide, CN, is an important free-radical mole-cule of one carbon chemistry, organic chemistry, free-radical chemistry and cosmochemistry. And the im-portant industrial processes, such as the Andrussovreaction, depend on the reactivity of CN bond[1]. Thechemistry of cyanide is also important in the surfacechemistry of a number of C- and N-containing sys-tems[1, . During the past decade, the adsorption of 2]CN and CN-containing molecules on transition metalsurfa…     

Adsorption Study of Methane on Activated Meso-carbon Microbeads by Density Functional Theory

A combined method of density functional theory (DFT) and statistics integral equation (SIE) for the determination of the pore size distribution (PSD) is developed based on the experimental adsorption data of nitrogen on activated mesocarbon microbead (AMCMB) at 77K. The pores of AMCMB are described as slit-shaped with PSD.Based on the PSD, methane adsorption and phase behavior are studied by the DFT method. Both nitrogen and methane molecules are modeled as Lennard-Jones spherical molecules, and the well-known Steele‘s 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. In order to test the combined method and the PSD model, the Intelligent Gravimetric Analyzer (IGA-003) was used to measure the adsorption of methane on the AMCMB. The DFT results are in good agreement with the experimental data. Based on these facts,we predict the adsorption amount of methane, which can reach 32.3ω at 299K and 4 MPa. The results indicate that the AMCMBs are a good candidate for adsorptive storage of methane and natural gas. In addition, the capillary condensation and hysteresis phenomenon of methane are also observed at 74.05K.     

A Density Functional Theory Study on the Adsorption of CN on Ni（Ⅲ） Surface

The interaction of cyanide (CN) with different sites on Ni(111) surface is studied by using density functional theory (DPT). Ni19 cluster is used to simulate the surface. The present calculations show that the end-on bonded (through C atom) configuration is much more preferable than the side-on bonded CN or other configurations on the same adsorption site. For all adsorption modes, adsorption energies at the top, bridge, and three-fold sites on Ni(111) are comparable, with the bridge site of the end-on bonded CN (through C atom) more favorable than other adsorption sites. CN vibrational frequencies are red-shifted at all cases, except that the end-on CN bonded(through C atom) on the top site is blue-shifted. The bonding of CN on the Ni(111) surface is largely ionic.     

Density Functional Theory Study on the Adsorption of HCNH and CNH2 on Cu（100） Surface

The HCNH and CNH2 adsorption on different coordination sites of Cu（100） was theoretically studied considering the cluster approach. The present calculations show that the bridge site is the most favorite for CNH2 perpendicularly adsorbed on the Cu（100） surface via the C atom. For HCNH absorbed on the Cu（100） surface, the parallel adsorption mode with the C and N atoms nearly directly above the adjacent top sites of Cu（100） surface is the most favored. Both CNH2 and HCNH are strongly bound to the Cu（100） surface with CNH2 which is lightly stable （2.51 kJ·mol^-1）, indicating that both species may be co-adsorbed on the Cu（100） surface.     

Density Functional Theory Study of Water Diffusion and Clustering on Pd（111）

1 INTRODUCTION The interaction of water molecules with metal sur- faces plays a vital role in a number of important pro- cesses, such as corrosion, heterogeneous catalysis, electrochemical processes in aqueous solutions, hydrogen production, etc.[1] The structure and pro- perties of water adsorbed on well-defined metal sur- faces have been the subject of numerous experi- mental and theoretical investigations. There have been a number of experimental studies of water on metal surfaces throu…     

Density Functional Theory Study on the Structural and Electronic Properties of Ge（SiO_2）_n Clusters

The geometry,stability,binding energy and electronic properties of(SiO2)n and Ge(SiO2)n clusters(n = 7) have been investigated by Density functional theory(DFT).The results show that the lowest energy structures of Ge(SiO2)n are obtained by adding one Ge on the end site of the O atom or the Si near end site of the O atom in(SiO2)n.The chemical activation of Ge-(SiO2)n is improved compared with(SiO2)n.The calculated second-order difference of energies and fragmentation energies show that the Ge(SiO2)n clusters with n = 2 or 5 are stable.     

How Does Acetylcholine Lose Trimethylamine? A Density Functional Theory Study of Four Competing Mechanisms

Low-energy collision-induced dissociation (CID) of acetylcholine (ACh) yields only two fragment ions: the dominant C(4)H(7)O(2)(+) ion at m/z 87, arising from trimethylamine loss; and protonated trimethylamine at m/z 60. Since the literature is replete with conflicting mechanisms for the loss of trimethylamine from ACh, in this article density functional theory (DFT) calculations are used to assess four competing mechanisms: (1) Path A involves a neighboring group attack to form a five-membered ring product, 2-methyl-1,3-dioxolan-2-ylium cation; (2) Path B is a neighboring group attack to form a three-membered ring product, 1-methyl-oxiranium ion; (3) Path C involves an intramolecular elimination reaction to form CO protonated vinylacetate; and (4) Path D is a 1,2-hydride migration reaction forming CH(2)-protonated vinylacetate. At the MP2/6-311++G(2d,p)//B3-LYP/6-31+G(d,p) level of theory path A is the kinetically favored pathway, with a transition-state energy barrier of 37.7 kcal mol(-1) relative to the most stable conformer of ACh. The lowest energy pathway for the formation of protonated trimethylamine was also calculated to proceed via path A, involving proton transfer within the ion-molecule complex intermediate, with the exocylic methyl group being the proton donor. To confirm the site of proton transfer, low-energy CID of acetyl-d(3)-choline (d(3)-ACh) was carried out, which revealed loss of trimethylamine and the formation of Me(3)ND(+).     

Adsorption and Reaction of CN + O → OCN on Cu(100) Surface: A Density Functional Theory Study

The adsorption and reaction of O + CN → OCN on Cu(100) are studied by using density functional theory and cluster model.Cu14 cluster model is used to simulate the surface.The calculated results show that the OCN species with the molecule perpendicular to the surface via N atom (N-down) is more favorable than other adsorption models, and the N-down at the bridge site is the most favorable.For N-down, calculated OCN symmetric and asymmetric stretching frequencies are all blue-shifted compared with the calculated values of free and in good agreement with the experiments.The charge transfer from the surface to the OCN species leads to that the bonding of OCN to the metal surface is largely ionic.The present studies also show that CN with the molecule perpendicular to the surface via C atom (NC-down) at the top site is the most stable.Except NC-down at the top site, the calculated CN stretching frequencies are all red-shifted.With O coadsorbed at the hollow site, the adsorption of NC-down at the next nearest bridge or top site is energetically more favorable than that at the adjacent hollow site.The reaction of O + CN → OCN on Cu(100) has no energy barrier via both Eley-Rideal and Langmuir-Hinshelwood processes.     

Density Functional Study on the Reaction Mechanism for the Reaction of Ni^＋ with Ethane

The mechanism of the reaction of Ni^ (^2D) with ethane in the gas-phase was studied by using density functional theory.Both the B3LYP and BLYP functionals with standard all-electron basis sets are used to give the detailed information of the potential energy surface (PES) of [Ni,C2,H6]^ . The mechanisms forming the products CH4 and H2 in the reaction of Ni^ with ethane are proposed.The reductive eliminations of CH4 and H2 are typical addition-elimination reactions.Each of the two reactions consists of two elementary steps:C-C or C-H bond activations to form inserted species followed by isomerizations to from product-like intermediate.The rate determining steps for the elimination reactions of forming CH4 and H2 are the isomerization of the inserted species rather than C-C or C-H bond activations .The elimination reaction of forming H2 was found to be thermodynamically favored compared to that of CH4.     

A Density Functional Study on the Geometries of Compounds Fe(HCN)_n~+ (n = 1～6)

1 INTRODUCTION The solvation of metal ion by different types ofsolvents is of great interest for a wide variety of app-lications[1]. In the experimental and theoretical inve-stigations, most of such studies are focused on ion-ligand systems complexed by…     

Catalytic Effect of Dimethylsulfoxide Complexes of Rh(III) and Ru(II) on the Polymerization of Vinyl Monomers Initiated by 2,2′-Azobisisobutyronitrile

Transition metal salts and complexes catalyze the polymerization of vinyl monomers in the presence or absence of 2,2′-azobisisobutyronitrile (AIBN). In this article the effect of some dimethyl sulfoxide complexes of Rh(III) and Ru(II) on the polymerization of vinyl monomers such as methyl methacrylate (MMA) and methyl acrylate (MA) initiated by AIBN is reported. The percentage conversion and the rate of polymerization of MMA and MA are found to increase rapidly with time. At the critical concentrations of the complexes, the percentage conversion and the rates of reaction are found to be higher than those with AIBN alone, which significantly proves their accelerating effect. At concentrations above and below that of the critical value, the percentage conversion and the rates of polymerization of MMA and MA are found to decrease from those with AIBN alone. The trend of the increase and decrease of the percentage conversion and the rate of reaction with both types of complexes are similar. The solvent used in the polymerization of MMA and MA is dimethylsulfoxide (DMSO) and the temperature of the reaction is 60°C. A precise mechanism for the catalytic reaction is suggested.     

A Density Functional Study on the Geometries of Compounds Fe(HCN)n+(n = 1～6)

The possible geometries of Fe(HCN)n+ (n = 1～6) compounds were studied by using DFT/UB3LYP/6-31G(2df) method. The structure and ground state of each fragmental ion are C∞v (4∑+ or 6∑+), D∞h(4∑g+), D3h (4A1'), C2v or Td or C3v (4A1), and D3h (4A1') or C4v( (2A1') sequentially with n = 1～5. For the compound Fe(HCN)6+, the possible geometry was not obtained. The sequential incremental interaction energy (-△(△E)), dissociation energy (△D0), enthalpy (-△(△H)) and Gibbs free energy (-△(△G)), and frequencies for HCN-Fe(HCN)n-1+ were also calculated, and the results are all in good agreement with the experiments. The bond length of Fe-N is lengthened with the increase of cluster size, and the strength of Fe+-N coordination bond varies nonmon- tonically as increasing the number of ligands. The Fe+-N bond of Fe(HCN)2+ is the strongest in all compounds.     

Study of H2O and HOCH2CH2OH Adsorption on the Relaxation Surface of β-Si3N4(0001) by Density Functional Theory

Density functional theory (DFT) B3LYP method is used to theoretically investigate the adsorption conformations of H2O and glycol on the relaxation surface of β-Si3N4(0001) with cluster models. For H2O, the most stable structure is that adsorbed through the H atom lying above a N(3) site of the relaxation surface of β-Si3N4(0001); while for glycol, it is the one adsorbed via the H atom lying above the center of Si(2) and N(3) of the same relaxation surface. The adsorption energy, adsorption bond and transfer electrons of the two adsorbed substances prove that glycol is easy to be adsorbed on the relaxation surface of β-Si3N4(0001).     

Density Functional Study of AunCo (n=1～7)

Cobalt-doped gold clusters Au_nCo (n=1～7) are systematically investigated for the possible stable geometrical configurations and relative stabilities of the lowest-lying isomers using density-functional theory at B3LYP/LanL2DZ level. Several low-lying isomers were deter-mined, and many of them are in electronic configurations with a high spin multiplicity. The results indicate that the ground-state Au_nCo (n=1～7) clusters adopt a planar structure except for n=7. The stability trend of the Au_nCo (n=1～7) clusters shows that the Au₂Co clusters are magic cluster with high stability.     

Density Functional Theory Study of C2Hx（x=4～6） Adsorption on the Fe（110） Surface

The density functional theory(DFT) and self-consistent periodic calculation were used to investigate the C2Hx(x = 4～6) species adsorption on the Fe(110) surface. The adsorption energy and equilibrium geometry of the species C2Hx(x = 4～6) on four possible sites(top,hcp,SB and LB) on the Fe(110) surface were predicted and compared. Mulliken charges and density of states analysis of the most stable site have been discussed. It is found that the species of C2H6 and C2H5 are adsorbed strongly on the Fe(110) surface with calculated adsorption energy of -80.24 and -178.89 kJ·mol-1 at the Fe-LB(long-bridge) ,respectively. However,the C2H4 is adsorbed strongly on the Fe(110) surface with calculated adsorption energies of -114.96 kJ·mol-1 at the top. The results indicate that the charge transferring process can be completed by chemisorption between Fe(110) surface and the species. Moreover,the chemical bands can be formed by chemisorptions between the Fe(110) surface and the species,too.     

Study of the Electrochemiluminescence Based on the Reaction of p-Hydroxyphenylpyruvic Acid with Tris(2,2'-bipyridine)ruthenium(Ⅱ)

p-hydroxyphenylpyruvic acid (pHPP) is an important intermediate in the metabolism of tyrosine. Under normal circumstances pHPF is readily converted to 2,5-dihydroxyphenylacetic acid by p-hydroxy-phenylpyruvate oxidase and the levels of pHPP encountered in blood and urine are extremely low. However, in a few individuals suffering from a congenital metabolic defect known as tyrosinemia, the oxidase is not available which leads to dramatic elevation of pHPP levels in blood and urine^[1]. Therefore, a selective and sensitive method for measuring pHPT is very useful for the diagnosis and treatment of such disease. In this paper the electrochemiluminescence(ECL) based on the reaction of pHPP with tris(2,2'-bipyridine)ruthenium(Ⅱ)[Ru(bpy)₃²⁺] in a flow injection system has been studied and a sensitive ECL method has been developed to detect pHPP in aqueous solution.     

1, 4-Pyrone Effects on O-H Bond Dissociation Energies of Catechols in Flavonoids: A Density Functional Theory Study

In recent years, there has been growing interest in selecting efficient antioxidants with low toxicity to reduce the damage of free radicals. Among these antioxidants, flavonoids have been paid much attention, owing to their excellent antioxidative and pharmacological activities1. Up to now, many efforts have been given to summarize the structure-activity relationships (SAR) for flavonoids. It has been widely accepted that two structural factors are critical for flavonoids to enhance the…     

Density Functional Study on the Mechanism of Collision Reaction among Protons, N2 and Water Vapor

The mechanism of collision reaction among protons, N2 and water vapor was theoretically studied using Density Functional Theory. The geometries of reactants, transition states, intermediates and products were optimized at the B3LYP/6-311 G^** level by the BERNY gradient analysis method. Transition states and intermediates have been identified by vibrational frequency analysis. The relationship among reactants, intermediates, transition states and products was affirmed by IRC calculation. The variations of energy and geometry along the IRC-determined reaction paths were described. The possible reaction pathways were represented and the optimal one was decided from the viewpoint of energy.