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The first theoretical investigation of the mechanisms for reactions of unsaturated hydrocarbons and the allied heterocyclic aromatics with the Si(111)-7x7 surface is reported. The density functional cluster model calculations predict stepwise, diradical pathways for these reactions.

Plasmon resonances and the plasmon-induced field enhancement (FE) in sodium nanoring dimers are investigated by time-dependent density functional theory. For larger separations, the optical absorption, the induced charge response and the frequency dependent current demonstrate that there are two capacitive coupling plasmon modes. One feature of FE is that, in the surface region of the nanoring, it has a very large maximum. Another feature of FE is that, along the perpendicular bisector of the line segment joining the two nanoring center points in the middle region of the nanoring dimers, it has maxima. With the decrease of the gap distance, because of the electrons tunneling across the dimer junction and screening, collective excitation modes are changed, and the charge transfer plasmon modes emerge in the nanoring dimers. FE induced by any plasmon modes decreases in the gap region. Moreover, corresponding to different gap distances, the high-energy plasmon resonance peak almost does not shift, because this plasmon mode is mainly the collective excitation as a result of interactions among degenerate individual electronic states. [ABSTRACT FROM AUTHOR]

The plasmon resonances and electron transport in linear sodium atomic chains are investigated using time-dependent density functional theory. The dipole response and dynamic conductance are obtained as a function of inter-atomic distance d and the chain length, under an impulse excitation polarized along the chains axis. We found that the current enhancement associated with the plasmon-induced field enhancement is mainly due to plasmon excitation of the hybridized bonding dipolar plasmons (BDP) mode. And the high energy plasmon modes are relatively weaker and are more delocalized in space than the BDP mode. The intensity of the dipole response and the current show an opposite tendency as the d is decreased while a same tendency is found as the number of atom increased. This can be understood from the competition between global quantization and local atomic confinement. [ABSTRACT FROM AUTHOR]

To understand the reaction mechanism involving hydrogen transfers through hydrogen-bond bridge, we carried out both Self-Consistent Charge Density Functional Tight-Binding (SCC-DFTB) calculations of bulk nitromethane and Density Functional Theory (DFT) calculations of singlet ground state/triplet excited state molecular nitromethane using B3LYP functional. Firstly, we tuned the repulsive parameters of the SCC-DFTB method for nitromethane with dataset calculated from DFT at B3LYP/6-311g level. The molecular dynamics simulations are carried out with tuned parameters to get the dynamical properties of the bulk nitromethane, and the static calculations are intended to give energy profile of the reaction process. These calculations indicate the excitation of nitromethane molecule making the proton transfer reactions possible, and lowering the reaction barrier. Proton transfer reactions in high pressure condensed phase are discussed by means of semi-empirical tight-binding and time-dependent density functional theory (TD-DFT). The energy as a function of reaction path between ground and excitation state NM is computed. These results indicate the excitation of nitromethane molecule making the proton transfer easy to happen. [ABSTRACT FROM AUTHOR]

In the present paper we give a detailed report on the results of our first-principles investigations of Ar adsorptions at the four high symmetry sites on M (111) (M = Pd, Pt, Cu, and Rh) surfaces. Our studies indicate that the most stable adsorption sites of Ar on Pd (111) and Pt (111) surfaces are found to be the fcc-hollow sites. However, for Ar adsorptions on Cu (111) and Rh (111) surfaces, the most favorable site is the on-top site. The density of states (DOS) is analyzed for Ar adsorption on M (111) surfaces, and it is concluded that the adsorption behavior is dominated by the interaction between 3s, 3p orbits of Ar atoms and the d orbit of the base metal atoms. [ABSTRACT FROM AUTHOR]

A systematic investigation into electronic and optical properties of ReN at ambient and high pressure by density functional theory with the generalized gradient approximation has been presented in this paper. Optical properties such as the dielectric function, refractive index, absorption, reflectivity, and electron energy-loss spectrum are obtained successfully. The features in the spectra of the optical parameters are analyzed in detail. [ABSTRACT FROM AUTHOR]

The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory (DFT). The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) method is used to describe the exchange-correlation energy in the present work. The calculated equilibrium lattice constant a0, bulk modulus B0, and the pressure derivative of bulk modulus B' 0 of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data. The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model, in which the phononic effect is considered, the relations of (V - V0)/V0 to the temperature and the pressure, and the relations of the heat capacity CV and the thermal expansion coefficient a to temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K. At low temperature, CV is proportional to T3 And tends to the Dulong-Petit limit at higher temperature. We predict that the thermal expansion coefficient a of NbN is about 4.20 X 10-6/K at 300 K and 0 GPa. [ABSTRACT FROM AUTHOR]

The adsorption behavior of H2 on the LiB (001) surface was investigated with density functional theory (DFT) method. It was found that the site of H2 adsorbed on the Li-B bridge II was easier than the other four sites (Li top, B top, hollow vertical and Li-B bridge I). H2 adsorbed on the Li-B bridge II site was a strong chemical adsorption. The adsorption energy was 2.190 eV, and the H, B atoms exhibited covalent characteristics, the H--H atoms have a little interaction, and the H2 was 0.331 Å below the surface of Li-B bridge II. The charge density, band structure, totals and partial density of states were calculated utilizing the first principle method. These calculations showed that the H interacted with the surface atoms, and partially saturated the dangling bonds with the surface atoms. The interaction between H and the surface atoms were mainly attributed to the H 1s, B 2s and B 2p states. The calculated band gap was 0.075 eV and 0.199 eV before and after adsorption. [ABSTRACT FROM AUTHOR]

Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT), we have investigated the crystal structures, elastic, and thermodynamic properties for Ti2SC under high temperature and high pressure. The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results. The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures. The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa. Investigations on the elastic properties show that the c axis is stiffer than the a axis, which is consistent with the larger longitudinal elastic constants (C33, C11) relative to transverse ones (C44, C12, C13). Study on Poisson's ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure. The ratio (B/G) of bulk (B) and shear (G) moduli as well as B/C44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure. Moreover, the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures. Again, we observed that the Debye temperature and Grüneisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen. [ABSTRACT FROM AUTHOR]

A theoretical study of structural and electronic properties of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX) crystal is performed using density functional theory. The band structure, the total density of states, the atomic orbit projected density of states (PDOS) of C, N, O, and H, and Mulliken population analysis are discussed. The study by analyzing the PDOS shows that the structure of BCHMX crystal possesses CH···O intra- and intermolecular hydrogen bonding. There are hydrogen bonds between H3-1s and O5-2p orbits, H2-1s and O6-2p orbits of intramolecules and between H2-1s and O1-2p orbits of intermolecules. The reasons for the smaller impact sensitivity compared with β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane and 1,3,5-trinitro-1,3,5-triazinane are also explored from the band gap in the crystal and the weakest bond dissociation energy in single molecule. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Bond dissociation energies (BDEs) for some nitro or amino contained prototypical molecules in energetic materials are computed by fixed-node diffusion quantum Monte Carlo method. The nodes are determined from a Slater determinant calculated within density functional theory at the B3LYP/6-311G** level. The possible errors, the nodal error, and the cancellation of nodal errors in calculating BDE are discussed, and the accuracy is compared with other available ab initio computations and experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: Elastic and thermodynamic properties of HfB2 with AlB2 structure under pressure are investigated by means of density functional theory method. The results at zero pressure are in good agreement with available theoretical and experimental values. The pressure dependence of elastic constants, bulk modulus and elastic anisotropy of HfB2 has been investigated. Through quasi-harmonic Debye model, the variations of the Debye temperature, heat capacity and thermal expansion with pressure and temperature are successfully obtained and discussed. [Copyright &y& Elsevier]

Using the first-principles pseudopotential method within a generalized gradient approximation of the density functional theory, the structural and electronic properties of SrSe and SrTe have been studied. The calculated lattice parameters are in excellent agreement with experimental values, whereas the error in the minimum gap value is as high as 43.25% in SrSe. To get reliable band gap values of SrSe and SrTe, we employ the GW (G is the Green's function and W is the screened Coulomb interaction) approximation method. The result in GW approximation improves the band gap value of the SrSe greatly and agrees with the value of experimental measurement. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of 0.25, 0.5 and 1 monolayer (ML) of the transition metal Ni on the metal substrate Al(110) was studied using first-principles calculations at the level of density functional theory. The metal–metal system was analyzed with the generalized gradient approximation. Four stable atomic configurations were considered, and the optimized geometries and adsorption energies of different Ni adsorption sites on the Al(110) surface at selected levels of coverage were calculated and compared. The four-fold hollow site was determined to be the most stable adsorption site with adsorption energy of 5.101eV at 0.25ML, 3.874eV at 0.5ML and 3.665eV at 1ML. The adsorption energies of the four sites slightly decreased as the Ni coverage increased. Work function analysis showed that when Ni is adsorbed on the Al(110) surface, the work function decreased as the coverage increased due to depolarization. The Mulliken population and density of states were calculated to determine the charge distribution of the adsorption site, confirming that a chemisorption interaction exists between the adsorbed Ni atom and Al(110) surface atoms. [Copyright &y& Elsevier]

Abstract: BC5 is a newly synthesized superhard material. We present a systematic investigation of optical properties of BC5 in P3m1 and I-4m2 phases at ambient and high pressure in the framework of density functional theory with the generalized gradient approximation (GGA) in this paper. Optical properties such as dielectric function, refractive index, absorption, reflectivity and electron energy-loss spectrum are obtained successfully. The feature in the spectra of the optical parameters is discussed. Through calculation, we find BC5 is optically anisotropic. Moreover, the dielectric function exhibits a large change at 70GPa pressure for P3m1 BC5 phase, but I-4m2 phase not, indicating the stable electronic structure that the I-4m2 phase possesses. [Copyright &y& Elsevier]

Abstract: The structural and electronic properties of the recently synthesized superhard BC5 are studied by using density functional theory within the generalized gradient approximation (GGA). P3m1-II structure is confirmed as the most stable state of BC5 by comparing three potential structures. The high-pressure effect on superhard BC5 is also successfully calculated. The obtained pressure dependence of structural property shows that the compressibility along three cell vectors is very close to each other. Based on the density of states (DOS), we find high pressure hardly change the DOS at Fermi level (EF ) which is related closely to the transition temperature Tc . The result is useful to further study the superconductivity of BC5. [Copyright &y& Elsevier]

Abstract: We present a systematic theoretical study for the structural, elastic and electronic properties of TaB2 with AlB2 structure under pressures ranging from 0GPa to 120GPa within the framework of density-functional theory in this paper. The results at zero pressure are in good agreement with available theoretical and experimental values. Our attention has been focused on high pressure behavior of TaB2. The pressure dependence of structure, elastic constants, Debye temperature, and density of states (DOS) are successfully calculated and discussed. [ABSTRACT FROM AUTHOR]

Abstract: A systematic theoretical study is presented for the structural and electronic properties of HfB2 with AlB2 structure under pressure ranging from 0 to 240GPa in the framework of density functional theory. The results at zero pressure are in good agreement with the available theoretical and experimental values. The pressure dependence of structural property shows that the effect of pressure is little on the structure of HfB2. The density of states (DOS) of HfB2 versus pressure is also successfully calculated. We find high pressure greatly changes the profile of the DOS, but it hardly changes the DOS value at Fermi level. Meanwhile, the Mulliken population analyses are investigated. It is suggested that as the pressure increases, a number of charge transfer from Hf to B atoms. [Copyright &y& Elsevier]

The first principle density functional theory method SIESTA has been used to compute the band gap of several polynitroaromatic explosives, such as TATB, DATB, TNT, and picric acid. In these systems, the weakest bond is the one between an NO2 group and the aromatic ring. The bond dissociation energy (BDE) alone cannot predicate the relative sensitivity to impact of these four systems correctly. It was found that their relative impact sensitivity could be explained by considering the BDE and the band gap value of the crystal state together. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Density functional theory calculation was carried out on cation-π complexes formed by cations [M = H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+] and π systems of annelated benzene. The cation-π bonding energy of Be2+ or Mg2+ with annelated benzene is very strong in comparison with the common cation-π intermolecular interaction, and the bonding energies follow the order Be2+ > Mg2+ > Ca2+ > Li+ > Na+ > K+. Similarly, the interaction energies follow the trend 1-M < 2-M < 3-M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with C&bond;H and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The properties of 2-Nitrimino-1-nitroimidazolidine are calculated by using SIESTA code, which adopts the standard Kohn-Sham self-consistent density functional method in the local density approximation. The structures and electronic properties are analyzed, and the factors that affect the impact sensitivity are discussed based on the crystal structure, band energy, and projected density of state. The reason for the smaller impact sensitivity compared to RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is also explored from several respects such as the weakest bond dissociation energy in single molecule, and hydrogen bond, band gap in the crystal. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

Abstract  We present density functionary theory (DFT) calculations on the structural parameters and electronic structure for iridium nitride by using the generalized gradient approximation (GGA) and the Perdew–Burke–Ernserhof (PBE) exchange-correlation functional. The lattice parameters and bulk modulus (B 0) for the ground state are obtained, and the energy band structure and electron densities of states (DOS) of IrN2 are presented. It is found that IrN2 has a very close indirect energy gap. There is a strong covalent bond between the two nearest N atoms. This gives rise to a very high elastic modulus of IrN2 and reveals the quasimolecular nature of the N2 in IrN2 crystal. Lattice parameters, bulk modulus, and the electronic structure of IrN2 under high pressure have also been investigated based on DFT. The compressibility along three cell vectors is very close to each other. The band gap increases a little with the pressure even when the pressure is up to 100 Gpa. [ABSTRACT FROM AUTHOR]

In this paper, we suggested a theoretical relationship between the property of molecular atomization energy and energy transfer rate in explosive detonation. According to the theory of Dlott and Fayer (J Chem Phys92(6):3798, 1990) some explosives are stable molecules with large energy barriers to chemical reaction in shock or impact initiation, so, a sizable amount of phonon energy must be converted to the molecular internal higher vibrations by multiphonon up pumping. To investigate the relationship between atomization energies and energy transfer rate, the number of doorway modes of explosives is estimated by their theory in which the rate is proportional to the number of normal mode vibrations. We evaluated frequencies of normal mode vibrations of TNB, TNAP, TNA, DATB, TATB, 2,4,6-trinitro-benzylalcohol (C7H5N3O7), and TNR by means of density functional theory (DFT) at the B3P86/6-31G(d, p) level. It is found that the number of doorway modes shows a linearly correlation to the atomization energies also calculated by means of DFT at the B3P86/6-31G(d, p) level. Besides, we studied the relation between the number of atoms and atomization energies for these molecules, and confirmed that for those secondary explosives molecules with similar molecular structure and similar molecular weight, the correlation between the atomization energy and the number of doorway modes is higher. This relationship is beneficial to the understanding of the property of explosive in detonation. [ABSTRACT FROM AUTHOR]

The heats of formation (HOFs) for 15 thiol compounds are calculated by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods with 6-311G** basis set and the complete basis set (CBS-Q) method. It is demonstrated that the B3P86 and CBS-Q methods are accurate to compute the reliable HOFs for thiol compounds. In order to test whether the B3P86 method has a low basis set sensitivity, the HOFs for six thiol compounds are also calculated by using the B3P86 method with 6-31+G*, 6-31+G**, and 6-311+G** basis sets for comparison. We also extend our study by employing the nonlocal BLYP method together with 6-31+G* basis set to calculate the HOFs for thiol compounds. The obtained results are compared with the experimental results. It is noted that the B3P86 method is not sensitive to the basis sets. Considering the inevitably computational cost of CBS-Q method and the reliability of the B3P86 calculation, the B3P86 method with a moderate or a larger basis set such as 6-311G** and 6-311+G** may be more suitable to calculate the HOFs of thiol compounds. In addition, we believe that the maximum error associated with the calculated HOFs is less than 6 kcal/mol for the B3P86/6-311G** method and it is expected that the error bar is more likely 1–5 kcal/mol for the HOFs of thiol compounds. [ABSTRACT FROM AUTHOR]

We compare the effectiveness of six exchange/correlation functional combinations (Becke/Lee, Yang and Parr; Becke-3/Lee, Yang and Parr; Becke/Perdew–Wang 91; Becke-3/Perdew–Wang 91; Becke/Perdew 86; Becke-3/Perdew 86) for computing C–N, O–O and N–NO2 dissociation energies and dipole moments of five compounds. The studied compounds are hexabydro-1,3,5-trinitro-1,3,5-triazine (RDX), dimethylnitramine, cyanogen, nitromethane and ozone. The Becke-3/Perdew 86 in conjunction with 6-31G** is found to give the best results, although for the dipole moments of RDX, there is a slightly difference that B3P86/6-31G** is less reliable than B3P86/6-31+G**. [Copyright &y& Elsevier]

Density functional theory calculations have shown that the open-shell metal−carbide endofullerene Sc3C2@C80 has the valence state (Sc3+)3(C2)3-@C806-. A lot of low-lying isomers differing in geometries and locations of the endohedral [(Sc3+)3(C2)3-] cluster have been located, indicating unusual dual intramolecular dynamic behaviors of this endofullerene at room temperature. The electrochemical redox properties of this endofullerene have been elucidated in terms of electronic structure theory. Its redox states are found to follow the general charge−state formula (Sc3+)3C2(3-q)-@C806- (q is the charge of the whole molecule ranging from +1 to −3), demonstrating the high charge flexibility of the endohedral metal−carbide cluster. The structure of the endohedral [(Sc3+)3C2(3-q)-] cluster varies with the redox processes, shifting from a planar structure (for q = 0 and −1) to a trifoliate structure (for q = +1, −2, −3). [ABSTRACT FROM AUTHOR]

Examines the chemical modification of diamond surfaces in the semiconductor industry. Evaluation by means of hybrid density functional method in combination with cluster model approach; Cycloadditions reactions to functionalize diamond surface at low temperature; Enhancement of reactivity on the surface to reduce overlaps.

The electronic ground states of ncyclacenes, as well as short-zigzag nanotubes, computed at unrestricted broken spin-symmetry density functional theory (UBS-DFT), were found to be open-shell singlets, rather than triplets. Computations for 6cyclacene at complete active space self-consistent field (CASSCF) and multireference perturbation theory (MRMP2) levels support this conclusion. Along with strain, the radical character of the open-shell singlet with antiferromagnetically coupled electron spins may contribute to the difficulties in synthesizing ncyclacenes. [ABSTRACT FROM AUTHOR]

Photodetachment of AgX- (X = Cl, Br, I) and AuCl- is studied by a photoelectron velocity map imaging technique and theoretical calculations. Photoelectron spectra (PES) and photoelectron angular distributions (PADs) were obtained. The vibrationally resolved spectra provided approximately equal electron affinities (EAs) for AgX: 1.593(22) eV for AgCl, 1.623(21) eV for AgBr, and 1.603(22) eV for AgI, respectively. Franck--Condon simulations of these spectra gave the equilibrium bond lengths and vibrational frequencies of the title anions. Relativistic density functional theory (DFT) calculations using BLYP, PW91, PBE, and BP86 functionals have been performed to predict the EAs of the AgX (X = Cl, Br, I) molecules. The computed EAs at the BP86 level of theory are in good agreement with the experimental values. Energy partitioning analyses (EPA) at the BP86(ZORA)/QZ4P level of theory of both anions and their neutrals were reported. [ABSTRACT FROM AUTHOR]

Abstract: Quantum chemical calculations are used to estimate the bond dissociation energies (BDEs) for nine alkyl nitrate and nitrite compounds. These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods with 6-31G∗ and 6-311G∗ basis sets. It is demonstrated that the B3P86/6-31G∗ is the most accurate method to compute the reliable BDEs for the compounds studied. In order to test whether the non-local BLYP method suggested by Luo [Y.R. Luo, Handbook of Bond Dissociation Energies in Organic Compounds, CRC Press, Boca Raton, 2003] is general for our study and whether B3P86 method is sensitive to the basis set, the BDEs for nine alkyl nitrate and nitrite compounds are also calculated by using BLYP/6-31+G∗ and B3P86 method with 6-31+G∗, 6-31++G∗ and 6-31G∗∗ basis sets for comparison. The obtained results are compared with the available experimental results. It is noted that the use of diffuse functions cannot improve the results and the use of polarization functions is more computationally effective than diffuse functions in the BDEs calculation. [Copyright &y& Elsevier]

Abstract: The reaction of to yield CrO+(2Σg /4Σg)+C2H4O, which is the continued research on the gas-phase reaction of with C2H4, has been investigated using density functional theory (DFT) at the UB3LYP/6-311++G(3df,3pd)//6-311G(2d,p) level. There is different reaction mechanism between the doublet and quartet PESs. A crossing seam between CP1 and CP2 is located. In addition, the crossing caused by SOC is efficient. The conclusion has been proved by the frontier molecular orbital interaction analyses about CP1 and CP2. [Copyright &y& Elsevier]

The La2@C72 and Sc2@C72 metallofullerenes have been characterized by systematic density functional computations. On the basis of the most stable geometry of 39 C72 hexaanions and the computed energies of the best endofullerene candidates, the experimentally isolated La2@C72 species was assigned the structure coded #10611. The good agreement between the computed and the experimental 13C chemical shifts for La2@C72 further supports the literature assignment (Kato, H.; Taninaka, A.; Sugai, T.; Shinohara, H. J. Am. Chem. Soc.2003, 125, 7782). The geometry, IR vibrational frequencies, and 13C chemical shifts of Sc2@C72 were predicted to assist its future experimental characterization. [ABSTRACT FROM AUTHOR]