Chemical Physics Letters (v.637, #C)
Editorial Board (CO2).
Poisson–Fermi model of single ion activities in aqueous solutions by Jinn-Liang Liu; Bob Eisenberg (1-6).
Display OmittedA Poisson–Fermi model is proposed for calculating activity coefficients of single ions in strong electrolyte solutions based on the experimental Born radii and hydration shells of ions in aqueous solutions. The steric effect of water molecules and interstitial voids in the first and second hydration shells play an important role in our model. The screening and polarization effects of water are also included in the model that can thus describe spatial variations of dielectric permittivity, water density, void volume, and ionic concentration. The activity coefficients obtained by the Poisson–Fermi model with only one adjustable parameter are shown to agree with experimental data, which vary nonmonotonically with salt concentrations.
Dielectric properties and alternating current conductivity of sol–gel made La0.8Ca0.2FeO3 compound by A. Benali; A. Souissi; M. Bejar; E. Dhahri; M.F.P. Graça; M.A. Valente (7-12).
In this work, single phase La0.8Ca0.2FeO3 nanomaterial has been synthesized by the sol–gel method using the citric acid route. By employing impedance spectroscopy, ac electrical properties have been measured over a temperature range from 300 to 673 K at various frequencies. With the analysis based on Debye's theory and a series of Arrhenius relations, the relaxation was argued to be associated with the hopping motions of charge carriers between Fe ions. The relaxation in the La0.8Ca0.2FeO3 compound was ascribed to be a polaronic relaxation. The ac electrical conduction was studied and associated to the non-overlapping small polaron tunneling (NSPT) model.
Entrance dynamics of CH4 molecules through a methane–water interface by Ezequiel L. Murina; Claudio Pastorino; Roberto Fernández-Prini (13-17).
Display OmittedWe studied the entrance mechanism of methane molecules into bulk water by Molecular Dynamics simulation over a broad time window. We corroborated that the presence of absorbed methane, under the studied thermodynamic state (298 K and roughly 10 MPa), does not influence the molecular configuration of water interface. Some representative interfacial trajectories were analyzed in detail and we propose an entrance mechanism in which interfacial water is not actively involved in the dissolution process. Finally, we described the Helmholtz Free Energy profile through the interface and obtained the dissolution free energy of methane in water.
Influence of nanoconfinement on the rotational dependence of line half-widths for 2–0 band of carbon oxide by A.A. Solodov; T.M. Petrova; Yu.N. Ponomarev; A.M. Solodov (18-21).
Absorption spectra of carbon oxide, confined in nanoporous silica aerogel, have been measured within 4100–4400 cm−1 region at room temperature and at several pressures using Bruker IFS-125 HR Fourier spectrometer. Dependence of the half-width (HWHM) values on rotational quantum numbers is studied and compared with the data available in literature. It is found that variations in the half-width values for the confined CO at small quantum numbers are larger than at moderate ones. The influence of confinement tightness on rotational dependence is discussed.
Enhancing proton conduction via doping of supramolecular liquid crystals (4-alkoxybenzoic acids) with imidazole by Ting Liang; Yong Wu; Shuai Tan; Xiaohui Yang; Bingzhuo Wei (22-25).
Doping of 4-alkoxybenzoic acids with 25 mol% imidazole resulted in mixtures exhibiting smectic C and nematic mesophases. The doping increased proton conductivities by 3 orders of magnitude.Enhancing proton conduction via doping was first achieved in hydrogen-bonded liquid crystals consisting of benzoic acids. Supramolecular liquid crystals formed by pure 4-alkoxybenzoic acids (nAOBA, n = 8, 10, 12) exhibited the maximum proton conductivity of 5.0 × 10−8 S cm−1. Doping of nAOBA with 25 mol% imidazole (Im0.25) had little impact on mesomorphism but increased proton conductivities by at least 3 orders of magnitude. The liquid crystals formed by nAOBA-Im0.25 exhibited the maximum proton conductivity of 1.9 × 10−4 S cm−1. It was proposed that structure diffusion of imidazole bridged interdimer proton transfer to form continuous conducting pathways in mesomorphic nAOBA-Im0.25.
Electron affinity and ionization potential of two-dimensional honeycomb sheets: A first principle study by Zexiang Deng; Zhibing Li; Weiliang Wang (26-31).
We perform first principle calculations based on density functional theory to study the electron affinity and ionization potential of two-dimensional structures of carbon family, group-III-nitride family and transition-metal dichalcogenide family. We found and explained the atomic number dependence of electron affinity and ionization potential.
Structure of nonuniform four-component fluid mixtures: A systematic investigation through density functional theory and simulation by Chandra N. Patra (32-37).
The density profiles of a four-component mixture near a hard wall as calculated from Density Functional Theory and Monte Carlo Simulation clearly reveals the surface segregation of larger components. Display OmittedThe static structure of four-component fluid mixtures is studied using a density functional approach and computer simulation. The input direct correlation function required in the simple weighted density approach is obtained analytically within the Percus–Yevick approximation. However, in the self-consistent density functional approach, the same is calculated numerically from the integral equation theory using a more consistent closure relation. The density profiles of the four-component hard sphere mixtures near a hard wall and around a large hard spherical solute as well as the radial distribution function of uniform system compare quite well with the computer simulation results over a wide variation of different parameters.
An initiation phenomenon of Al-PTFE under quasi-static compression by Bin Feng; Xiang Fang; Yu-chun Li; Huai-xi Wang; Yi-ming Mao; Shuang-zhang Wu (38-41).
SEM and finite element simulation results suggest that the initiation of Al-PTFE under quasi-static compression was directly related to crack propagation and sliding interfaces in severely sheared regions.Generally, the Al-PTFE is thought to be inert under quasi-static or static loads. However, here we reported an initiation phenomenon of Al-PTFE under quasi-static compression. SEM and finite element simulation results suggest that the initiation was directly related to crack propagation and sliding interfaces in severely sheared regions. Calculation results show that the deformation induced temperature rise is only 28.6 °C and no melted Al or PTFE were observed in recovered samples in the critical initiation state. Therefore, the initiation is more like a mechanochemical process rather than a thermochemical one.
Thermodynamic and kinetic stability of zwitterionic histidine: Effects of gas phase hydration by Sung-Sik Lee; Ju-Young Kim; Yuna Han; Hyun-Jin Shim; Sungyul Lee (42-50).
We present calculations for histidine–(H2O) n (n = 0–6) to examine the effects of micro-hydrating water molecules on the relative stability of the zwitterionic vs. canonical forms of histidine. We calculate the structures and Gibbs free energies of the conformers at wB97XD/6-311++G(d,p) level of theory. We find that six water molecules are required to produce the thermodynamically stable histidine zwitterion. By calculating the barriers of canonical ↔ zwitterionic transformation, we predict that both the most stable canonical and zwitterionic forms of histidine–(H2O)6 may be observed in low temperature gas phase environment.
Approaching the double-faceted nature of the CX bond in halobenzenes with a bifunctional probe by Krystel El Hage; Jean-Philip Piquemal; Zeina Hobaika; Richard G. Maroun; Nohad Gresh (51-57).
In halobenzenes, the CX bond (X = Cl, Br) is doubly faceted, electron-deficient along the CX direction, and electron-rich on its flanks. We have recently shown that both features could be enhanced by appropriate electron-withdrawing and electron-donating groups, respectively. In this letter we further highlight this dual character by approaching a bifunctional probe, N-methylformamide, to both regions in representative substituted halobenzenes. We report the results of interaction energy computations, ELF, and NCI analyses. These methods used in conjunction show the responsiveness of the CX bond to both kinds of substitutions, enabling significant interaction energy gains with respect to the parent compound.
Layer number dependence of carrier lifetime in graphenes observed using time-resolved mid-infrared luminescence by Hiroshi Watanabe; Tomohiro Kawasaki; Takushi Iimori; Fumio Komori; Tohru Suemoto (58-62).
Femtosecond luminescence of 1-, 2-, and 6–8-layer graphenes as well as graphite (n = ∞) is studied in the near- to mid-infrared region, using a luminescence up-conversion method. The luminescence decay profiles show non-exponential behaviors within several picoseconds. Compared to graphite, 1- and 2-layer graphenes exhibit a remarkable reduction of lifetime at 0.3 eV. A two-temperature model that considers an effective Fermi energy successfully reproduces the decay profiles. On the basis of the Fermi energy (0.2 eV) of 1-layer graphene obtained from the photoemission experiment, we ascribe the layer number dependence of lifetime to the effective Fermi energy difference.
The complex kinetics of the ice VI to ice XV hydrogen ordering phase transition by Jacob J. Shephard; Christoph G. Salzmann (63-66).
The reversible phase transition from hydrochloric-acid-doped ice VI to its hydrogen-ordered counterpart ice XV is followed using differential scanning calorimetry. Upon cooling at ambient pressure fast hydrogen ordering is observed at first followed by a slower process which manifests as a tail to the initial sharp exotherm. The residual hydrogen disorder in H2O and D2O ice XV is determined as a function of the cooling rate. We conclude that it will be difficult to obtain fully hydrogen-ordered ice XV by cooling at ambient pressure. Our new experimental findings are discussed in the context of recent computational work on ice XV.
Effect of [PO4]3−/[VO4]3− substitution on the structure and luminescence properties of Ca5[(P,V)O4)]3F:Eu3+ phosphors by Tongrong Deng; Zhiguo Xia; Hao Ding (67-70).
The variation of the emission and excitation spectra of Ca5[(P,V)O4)]3F:Eu3+ phosphors depending on the varied [PO4]3−/[VO4]3− substitution amounts have been also discussed.Ca5[(P,V)O4)]3F:Eu3+ red-emitting phosphors were synthesized by a solid-state method. The effect of [PO4]3−/[VO4]3− substitution on the structures and luminescence properties have been discussed. Apatite-type Ca5[(P,V)O4)]3F:Eu3+ phosphors are obtained, and the lattice parameters a, c values and cell volume V increase with the increasing content of [VO4]3− substitution for [PO4]3−. The optimum Eu3+ doping concentration in a selected system has been studied. The variations of the emission and excitation spectra of Ca5[(P,V)O4)]3F:Eu3+ phosphors depending on the varied [PO4]3−/[VO4]3− substitution amounts have been discussed. The mechanism on the broadening of the excitation band with increasing [VO4]3− contents has been analyzed.
Stability improvement of C8H2 and C10H2 embedded in poly(vinyl alcohol) films with adsorption on gold nanoparticles by Kang An; Guotong Wei; Gongmin Qi; Leimei Sheng; Liming Yu; Wei Ren; Xinluo Zhao (71-76).
The surface-enhanced Raman scattering (SERS) spectra of size-separated polyynes C2n H2 (n = 4–6) are reported via using gold nanoparticles as the SERS enhancer for the first time in colloids and poly(vinyl alcohol) films. The observed SERS bands show significantly improved signals and stability for at least 6 months in films. And the thermal stability of C8H2 is better than that of C10H2 and C12H2. The theoretical Raman modes of gold-capped polyynes are investigated by density functional theory. From the Au LIII-edge X-ray absorption spectra, differences were found after adding polyynes to Au colloids or PVA films.
Vibrational spectra and conformational analysis of desflurane. A cryosolution and ab initio study by S.M. Melikova; K.S. Rutkowski; B. Czarnik-Matusewicz; M. Rospenk (77-82).
The vibrational spectra of desflurane are studied with the help of FTIR cryospectroscopy in liquefied Kr at T ∼ 120–160 K and Raman spectroscopy of pure liquid. Particular IR bands reveal qualitative temperature changes of conformational origin. Only two of the six stable conformers found in MP2/6-311++G(d,p) calculations contribute to the spectra. The calculated vibrational spectra reflect the basic features of experimental spectra. IR spectra of two component cryosolutions suggest weak complex formation between desflurane and methyl fluoride stabilized by ‘blue shifting’ H bonds.
The effect of protonation site and conformation on surface-induced dissociation in a small, lysine containing peptide by Kulsum Shaikh; Jacob Blackwood; George L. Barnes (83-87).
Display OmittedSimulations of surface induced dissociation (SID) of protonated peptides have provided significant insight into the energy transfer and mechanism of SID; however, they have been limited to glycine and alanine containing peptides. The chemical simplicity of these systems forces N-terminus protonation. Here we present results from simulations involving a lysine containing peptide that allowed for multiple protonation sites and conformations. We found that when the excess proton is located on the basic lysine side chain, fragmentation dynamics are typically slower and occur through a ‘charge-remote’ pathway. Additionally, conformation alone has a significant effect on the observed proton transfer pathways.
Negativity of Fukui function of some isolated s and p block elements: The role of orbital relaxation effect by Rituparna Bhattacharjee; Ram Kinkar Roy (88-93).
In the present article, we emphasize the correlation between orbital relaxation effect and nature of atomic Fukui functions. While doing so, f − ( r ¯ ) and f + ( r ¯ ) values are found to be positive and negative, respectively, for the chosen s block elements. Also, f − ( r ¯ ) and f + ( r ¯ ) values for chosen p block atoms are negative. Nodal nature of the highest occupied and lowest unoccupied orbitals, electron–electron repulsion and effective nuclear charge become handy in explaining the observed trends. Out of track results obtained for the inert atoms are also explained.
Thermodynamic considerations in the formation of Janus-like TaSi2/Si nanoparticles by electron-beam evaporation by Andrei V. Nomoev; Alexander R. Radnaev; Boris B. Baldanov; Nicolai A. Torhov; Bair R. Radnaev; Nicolai A. Romanov; Makoto Schreiber (94-96).
The mechanism of formation of TaSi2/Si Janus nanoparticles from gas-phase tantalum and silicon produced through an electron-beam evaporation technique is re-evaluated using thermodynamic arguments. This new proposed mechanism may make it possible to predict other two-component systems which can produce Janus nanoparticles through electron-beam evaporation and other high-temperature gas-phase synthesis techniques.
QM/MM study on the aging mechanism of dichlorvos-inhibited acetylcholinesterase by Xiaowen Tang; Ruiming Zhang; Qingzhu Zhang; Wenxing Wang (97-102).
The aging mechanism of acetylcholinesterase (AChE) inhibited by dichlorvos has been studied by using a combined quantum mechanics/molecular mechanics (QM/MM) computation. The doubt whether His447 should be protonated or not during the aging process was investigated. The results show that the exponential average barrier of the aging reaction with His447 in unprotonated state is 8.4 kcal/mol lower than that in protonated state, suggesting that His447 should be unprotonated during the aging process of dichlorvos-inhibited AChE. The further analysis reveals that residues Gly122 and Ala204 can facilitate the reaction through dispersing the charge and stabilizing the transition state.
A molecular simulation study of the glass transition of cross-linked poly(dicyclopentadiene) networks by Robert M. Elder; Jan W. Andzelm; Timothy W. Sirk (103-109).
Cross-linked polymer networks are widely used as structural and protective materials, which require strength and toughness. Experiments have shown that cross-linked poly(dicyclopentadiene) (pDCPD) networks provide similar strength but superior fracture toughness relative to commonly-used network chemistries like epoxy. To better understand pDCPD, we use atomistic molecular dynamics to study the properties of pDCPD networks across the glass transition as a function of molecular weight between cross-links. Moreover, we identify molecular mechanisms that potentially control mechanical and transport properties. The alpha-relaxation (the glass transition) is linked to intra-chain motions and large-scale segmental motions, while sub-T g relaxations are linked with more localized motions.
Structure and stability of multiply occupied methane clathrate hydrates by Jinxiang Liu; Haiying Liu; Jiafang Xu; Gang Chen; Jun Zhang; Shoushan Wang (110-114).
The structure, stability and occupancy of methane hydrates were studied by the method of ab initio molecular dynamics simulation combined with quantum chemistry calculation. The optimum occupancy for five clathrate cages (512, 435663, 51262, 51264 and 51268) is one, one, one, two, and five methane molecules, respectively, suggesting that just 51264 and 51268 cages are likely to form the multiply occupied methane hydrates. Moreover, our results show that the methane molecules in the large cage aggregate to form a cluster, which would be helpful to understand the formation of multiply occupied hydrates.
Theoretical analysis on the aromaticity of uracil: Important electronic configurations and solvent effect on the aromaticity by Taro Udagawa (115-119).
Aromaticity and the important electronic configurations of uracil are studied by index of deviation from aromaticity (IDA) and CiLC (CI/LMO/CASSCF) analysis. The calculated IDA values of uracil are 5.256 and 4.998 in gas phase and in solvent model, respectively. These large IDA values indicate that uracil is almost completely non-aromatic even in solvent. The CiLC analysis has revealed that main ionic electronic configurations of uracil involve charge transfer from endocyclic neighboring carbon atom to exocyclic oxygen atom.
Behavior of the Sapporo-nZP-2012 basis set family by Rebecca Weber; Benjamin Hovda; George Schoendorff; Angela K. Wilson (120-126).
The behavior of Sapporo-nZP-2012 (n = D, T, Q) basis sets for 3d atoms is investigated. It is shown that total atomic energies obtained using Sapporo sets of increasing quality converge to a limit. Several schemes are used to determine these limits and comparisons are made to numerical Hartree–Fock energies and to limits obtained with correlation consistent sets (cc-pVnZ, n = T, Q, 5). While differences in energy relative to numerical HF are larger for Sapporo-nZP-2012 sets (16–40 mEh) than for correlation consistent basis sets (∼0.005 mEh), the systematic nature of the Sapporo-nZP-2012 sets may provide a reasonable alternative when the correlation consistent basis sets are not available.
Effects of Bi3+ ions on luminescence of dumbbell-like SrMoO4 and SrMoO4:Eu3+ microcrystals by Yanhong Bai; Chunyan Bai; Guoli Mo (127-131).
Bi3+ doped SrMoO4 and SrMoO4:Eu3+ microcrystals are synthesized by the precipitation method at room temperature. The synthesized samples show pure tetragonal phase with an I41/a space group. The TEM images indicate that all samples have the morphology of dumbbell. The doping Bi3+ ions for SrMoO4 induce the decreases of excitation and emission intensities. But enhanced red emission for SrMoO4:Eu3+ is obtained by co-doping Bi3+ ions. For a fixed Eu3+ concentration of 3.0%, there is an optimal Bi3+ concentration, at which the maximum emission intensity is obtained. The optimal concentration of Bi3+ is 2.0% for SrMoO4:3.0%Eu3+.
Studies on electrochemical properties of CuO–In2O3 based nanocomposites by G. Mohan Kumar; A. Madhan Kumar; P. Ilanchezhiyan; T.W. Kang (132-136).
CuO–In2O3 based nanocomposites were synthesized through a facile wet chemical approach and their structural/morphological characteristics were investigated using X-ray diffraction and transmission electron microscopic measurements, respectively. The composites were drop cast over transparent conducting substrates (from colloidal media) at room temperature to fabricate the working electrodes for electrochemical studies. The charge transfer resistance, nature of charge carriers, flat band potential and carrier density of CuO–In2O3 was determined using Nyquist and Mott–Schottky plots. The potential of solution processed CuO–In2O3 nanocomposites for electronic functions was evaluated by fabricating heterojunction diodes based on p-CuO–In2O3/n-Si architectures. Their diode characteristics revealed an excellent rectifying behaviour.
Effects of morphology and surface area of the oxide nanostructures on the visible–light induced generation of hydrogen in ZnO(TiO2)/Cd1 − x Zn x S and ZnO(TiO2)/Pt/Cd1 − x Zn x S heterostructures (x = 0.0, 0.2) by Anand Roy; S.R. Lingampalli; Sujoy Saha; C.N.R. Rao (137-142).
Hydrogen can be generated by visible light irradiation of semiconductor heterostructures of the type ZnO/Pt/CdS and TiO2/Pt/CdS. In order to understand the dependence of hydrogen generation on the properties of the nanoparticles of ZnO and TiO2, we have carried out systematic studies. For this purpose, we have studied photocatalytic hydrogen generation by ZnO(TiO2)/Cd1 − x Zn x S and ZnO(TiO2)/Pt/Cd1 − x Zn x S (x = 0.0, 0.2) heterostructures with oxide nanostructures possessing different morphologies and surface areas. In the case of TiO2/Pt/Cd0.8Zn0.2S heterostructures, the highest H2 evolution rate up to1.76 mmol h−1 g−1 were obtained with H2Ti3O7 nanotubes, with the least H2 evolution rate (0.55 mmol h−1 g−1) from TiO2 powder (Degussa P25). In the case of ZnO/Pt/CdS heterostructures, the highest H2 evolution rate (6.88 mmol h−1 g−1) were obtained from ZnO nanorods1, whereas the least H2 evolution rate (2.55 mmol h−1 g−1) was obtained from ZnO nanorods3. The photocatalytic activity of heterostructures generally follows the trend in BET surface areas of the oxide nanostructures, with high surface area favoring good hydrogen evolution activity.
Efficient prediction of high spin ground state stability in organic polyradicals under solvent effects by Xun Zhu; Yuriko Aoki (143-147).
When designing organic ferromagnets in nano- and bio-systems, it is essential to account for solvent effects as most biological reactions occur in water. The minimized mixing elongation (MMELG) method was combined with the polarizable continuum model (PCM) for accurate and efficient electronic structure calculations of the lowest and highest spin states of huge systems with solvent effects. The MMELG-PCM-L min method that combined the MMELG-PCM method and the L min method can be efficiently and reliably applied to predict the high spin ground state stability of conjugated organic polyradicals and is thus useful for designing organic ferromagnets with solvent effects.
Vibronic emission spectrum of 2-chloro-6-fluorobenzyl radical produced in corona discharge by Young Wook Yoon; Sang Youl Chae; Manho Lim; Sang Kuk Lee (148-152).
We generated vibronically excited but jet-cooled 2-chloro-6-fluorobenzyl radical from precursor 2-chloro-6-fluorotoluene seeded in a large amount of helium carrier gas using a pinhole-type glass nozzle coupled with a technique of corona excited supersonic jet expansion. From an analysis of the visible vibronic emission spectrum observed, we found evidence of the formation of the 2-chloro-6-fluorobenzyl and 2-fluorobenzyl radicals, and determined the electronic energy in the D1 → D0 transition and the vibrational mode frequencies of the 2-chloro-6-fluorobenzyl radical in the ground electronic state, for the first time, by comparison with ab initio calculations of the precursor molecule.
The influence of carbon hybridization on coupling constants across C―X⋯Cl―F dihalogen bond: A computational study by Hamid Reza Masoodi; Sotoodeh Bagheri (153-158).
The results of a theoretical study concern with the question of how carbon hybridization affects coupling constants across 13C―X⋯35Cl― 19F (X = 19F, 35Cl, 79Br) dihalogen bond are demonstrated in the present work. The NMR calculations are performed at B3LYP/aug-cc-pVTZ and PBE0/aug-cc-pVTZ levels. Here, halomethanes, haloethylenes and haloacetylenes are considered as halogen acceptor and ClF as halogen donor. Similar to |ΔE|, 1XJX―Cl and |2XJX―F| (with the exception of |2XJCl―F|) increase as follows: C(sp3) > C(sp2) > C(sp). An opposite order is observed for 1JCl―F. Also, the changes of |2XJCl―F| are negligible and irregular.
Quasi-superhydrophobic porous silicon surface fabricated by ultrashort pulsed-laser ablation and chemical etching by Huaihai Pan; Fangfang Luo; Geng Lin; Chengwei Wang; Mingming Dong; Yang Liao; Quan-Zhong Zhao (159-163).
A silicon surface with distinctive structures is fabricated by ultrashort pulsed-laser ablation and chemical etching with acidic fluoride solutions. The surface consists of micro/nanostructures that result in the quasi-superhydrophobicity of the silicon surface. By fine tuning a key process parameter (i.e., pulsed laser power), surfaces with different wettability are fabricated. The morphology and composition of the surfaces are characterized by scanning electron microscopy, which reveals nanopores. The contact angle of water on these surfaces was measured and found to be as high as 150° at optimized parameters. This work presents a novel process of fabricating a silicon-based quasi-superhydrophobic porous surface.
Electronic structure and second hyperpolarizability of M(NA2)2 (M = Be, Mg, Ca; A = H, Li, Na) complexes by Paramita Banerjee; Prasanta K. Nandi (164-171).
The ground state structure and NLO properties of hydrazine molecule, metal diamine complex M(NH2)2 and its derivatives M(NA2)2 (M = Be, Mg, Ca and A = Li, Na) are calculated by using different DFT functionals and basis sets. The chosen species are sufficiently stable. The M(NA2)2 complexes (A = Li, Na) have rather larger magnitude of third-order response property compared to the hydrazine molecule and M(NH2)2 complexes. The sum-over-state (SOS) calculated one-photon and two-photon part of second-hyperpolarizability showed almost identical pattern of variation as obtained in the DFT calculated results. The largest second-hyperpolarizability is predicted for the complex Ca(NNa2)2.
Elucidating the high-k insulator α-Al2O3 direct/indirect energy band gap type through density functional theory computations by R.C.R. Santos; E. Longhinotti; V.N. Freire; R.B. Reimberg; E.W.S. Caetano (172-176).
Display OmittedThe measured band gap of the high-k insulator α-Al2O3 is direct (8.80 eV) but previous theoretical estimates were not conclusive regarding its direct/indirect character. Thus, we have performed density functional theory (DFT) computations of the structural and electronic properties of α-Al2O3 employing several exchange-correlation functionals and the Δ-sol scheme. Among the functionals tested, the best results were obtained for the sX-LDA calculation, which predicted an indirect gap of 8.826 eV. The lattice parameter dependence of the α-Al2O3 gap type, on the other hand, suggests a subtle transition for temperatures above 400 K due to thermal expansion.
Metal–ion binding by cyclic halogen-bonded structures: A theoretical study using M–(BrZ)4 clusters (Z = F or NH2; M = Li+, Na+, or Mg2+) by Ruben D. Parra (177-181).
Molecular Graph for Mg2+–(BrF)4 showing bond paths and critical point electron densities.The ability of a cyclic halogen-bonded network to bind a metal ion is explored using M–(BrZ)4 complexes (M = Li+, Na+, or Mg2+; Z = F or NH2). Binding is characterized by bond paths connecting the metal ion with each one of the bromine atoms in the host, and orthogonal to the Br…Z interactions. Binding energies are substantial and follow the order Na+ < Li+ ≪ Mg2+. The electron densities at the Br…M bond critical points are generally smaller than their Br…Z counterparts for the monovalent ions, but significantly larger for Mg2+. Both Br…M and Br…Z interactions are found to be non-covalent in nature.
Chemisorption of benzene on Pt (1 1 1) surface: A DFT study with van der Waals interaction by P.K. Ayishabi; K.G. Lakshmikanth; Raghu Chatanathodi (182-188).
We perform periodic Density Functional Theory (DFT) calculations to study adsorption of benzene on a Pt (1 1 1) surface. van der Waals (vdW) interaction is included using vdW-DF functionals. Benzene is found to chemisorb strongly, and we obtain adsorption energy and geometry at all possible unique orientations on Pt (1 1 1) surface which agree well with experiments and previous calculations. We also find that while vdW interaction is crucial to the energetics of adsorption of benzene on Pt (1 1 1), the equilibrium geometry of the adsorbed molecule and its electronic structure are not so sensitive to this interaction.
Use of liquid crystals for imaging different inclusion abilities of α-cyclodextrin and β-cyclodextrin toward cetyltrimethyl ammonium bromide by Zhijian Liao; Sinan Du; Zhenli Qin; Jinyan Wang; Fang Zuo; Jianbin Luo (189-194).
We herein report a method for the imaging of different inclusion abilities of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) toward cetyltrimethyl ammonium bromide (CTAB) using liquid crystals (LCs). The optical transition from the dark to the bright state was caused by the inclusion interaction between CTAB and CDs. It was confirmed that α-CD formed more stable CTAB complexes than β-CD, leading to different optical responses of the LCs from the α-CD/CTAB and β-CD/CTAB systems. This method could be used to provide a visual method for selection of the correct CD molecules for interaction with surfactant molecules in recognition systems.
Keywords: Cyclodextrins; Cetyltrimethyl ammonium bromide; Inclusion phenomena; Liquid crystal; Optical response; Orientational transition;