Chemical Physics Letters (v.516, #4-6)
Editorial Board (IFC).
Ambiguities in surface nonlinear spectroscopy calculations by Steven J. Byrnes; Phillip L. Geissler; Y.R. Shen (115-124).
Display Omitted► We explain ambiguities in simulations of nonlinear optical surface spectroscopy. ► There is an ambiguity in the definition of the electric-dipole-order surface signal. ► There is also an ambiguity in the definition of the quadrupole-order bulk signal. ► These two ambiguities are equal and opposite, so the total signal is unambiguous. ► Our simulations of the water–air interface support this picture.Recent molecular simulations of liquid interfaces yield surface sum-frequency vibrational spectra that can be highly sensitive to the seemingly-arbitrary choice of molecular center in the calculation method. We show that the ambiguity arises because widely-used approaches, focusing exclusively on electric-dipole contributions from the surface, neglect coordinate-dependent quadrupole-order contributions of comparable magnitude from the bulk. The correct calculation includes both surface and bulk responses. With a judicious choice of molecular center, however, it may be possible to minimize the bulk contribution, allowing the surface-only calculation to produce a reasonably accurate spectrum. We use water as an example to elucidate the problem.
Gaussian basis set of sextuple zeta quality for hydrogen through argon by C.T. Campos; G.A. Ceolin; A. Canal Neto; F.E. Jorge; F.N.N. Pansini (125-130).
Convergence of the CCSD(T) atomization energy for carbon tetrafluoride as a function of basis set size.Display Omitted► Accurate CCSD(T)/6ZP–DKZ atomization energies for a sample of molecules. ► Scalar relativistic effect estimates. ► Estimates for the heat of formation of gaseous boron and carbon tetrafluoride. ► Electric property calculations.Segmented all-electron contracted sextuple zeta valence plus polarization function (6ZP) basis sets for the elements from H to Ar were constructed to be used in conjunction with the non-relativistic and Douglas–Kroll–Hess Hamiltonians. The scalar relativistic effect at the coupled cluster level of theory on atomization energy for a sample of molecules was discussed. Additional improvements in the atomization energies were achieved by applying corrections due to core/valence correlation, atomic spin–orbit effects, and addition of tight d and f functions on second-row elements. This leads to estimates for the heat of formation of gaseous boron and carbon tetrafluoride.
CI potential energy curves for three states of RuO2+ by Jeffrey L. Tilson; Walter C. Ermler; Robert J. Fowler (131-136).
Display Omitted► Accurate potential energy curves for RuO2+ from spin–orbit configuration interaction calculations. ► Electronic spectra and spectroscopic constants are reported. ► Molecular wave functions are analyzed in terms of the bonding of d electrons.Three low-lying states of RuO2+ are analyzed using large-scale configuration interaction (CI) calculations based on multireference wavefunctions. Relativistic effects are included using relativistic effective core potentials and a spin–orbit (SO) CI approach. The ground state is predicted to be a triply bonded system of 0+ (1Σ+) symmetry having a dissociation energy of 83.8 kcal/mol, an equilibrium bond length of 1.55 Å and a vibrational frequency of 1227 cm−1. Two close-lying states (3Φ) and (3Δ) states have dissociation energies, bond lengths and frequencies of 82.2 and 68.5 kcal/mol, 1.83 and 1.90 Å, and 974 and 974 cm−1, respectively. The states differ in energy at their respective minima by 551 and 4777 cm−1.
Classical versus quantum vibrational state distributions for the benchmark polyatomic reaction OH + D2: Checking the validity of the QCT method by L. Bonnet; J. Espinosa-García; J.C. Corchado; S. Liu; Dong H. Zhang (137-140).
Display Omitted► The QCT method is applied to the benchmark tetratomic reaction OH + D2. ► Comparison with exact quantum scattering calculations is performed. ► Standard as well as Gaussian binning procedures are tested.We report quasi-classical trajectory (QCT) and exact quantum scattering (EQS) calculations on the title process performed on the Ochoa–Clary potential energy surface. Total angular momentum was kept at zero for simplicity’s sake. The product vibrational state distributions obtained from the two approaches are found to be in good agreement. In particular, the third most populated state is significantly less probable than observed experimentally for both methods. The present study tends to rule out the possible failure of the classical description as the source of the discrepancy with experimental measurements.
A density-functional-theory study of biradicals from benzene to hexacene by Hyun-Jung Kim; Xingyong Wang; Jing Ma; Jun-Hyung Cho (141-145).
Display Omitted► Calculated singlet–triplet energy gap of biradicals in polyacenes by means of density-functional theory. ► The singlet–triplet gap monotonically increases with increasing the length of polyacene. ► Spin delocalization affects the singlet–triplet gap. ► Spin delocalization of singlet state is mediated by a spin polarization of p z orbitals.The singlet–triplet energy gap of biradicals created in benzene and polyacenes is investigated by density-functional-theory calculations. For the biradicals in benzene, naphthalene, anthracene, tetracene, pentacene, and hexacene, we find that the singlet state is energetically favored over the triplet state by 189, 191, 184, 199, 218, and 244 meV, respectively. The monotonous increase of the singlet–triplet energy gap from anthracene to hexacene is attributed to the enhanced stability of the singlet state for longer polyacenes. Our analysis shows that the spin density of the singlet state is delocalized over all benzene rings, but such a spin delocalization is not present for the triplet state.
Theoretical studies of nickel atoms and nickel(II) ions coordinated with CO and BF ligands by Sean A.C. McDowell; A. David Buckingham (146-148).
Display Omitted► Energetically stable complexes of Ni with BF were predicted. ► Sequential replacement of CO by BF increases stability of Ni complex. ► CO stretch is red-shifted whilst BF stretch is blue-shifted in the Ni complexes.A computational study of a neutral Ni atom and Ni(II) atoms coordinated with CO and BF ligands was undertaken using density functional theory. Neutral compounds with general formula Ni(CO) x (BF)4− x (x = 0–4) were predicted to have tetrahedral geometries, and cationic Ni ( CO ) x ( BF ) 4 - x 2 + square-planar geometries. Sequential replacement of the CO molecules in the well known tetrahedral Ni(CO)4 molecule yields a substantially more stable tetrahedral Ni(BF)4 molecule, and substitution of the CO ligands in the square-planar [Ni(CO)4]2+ cation yields a more stable [Ni(BF)4]2+ analogue. Stable complexes were also obtained by substitution of the OC ligands by FB in the [Ni(OC)4]2+ cation.
Tautomerism in 5-methyltetrazole investigated by core-level photoelectron spectroscopy and ΔSCF calculations by R.M. Pinto; A.A. Dias; M. Coreno; M. de Simone; B.M. Giuliano; J.P. Santos; M.L. Costa (149-153).
Display Omitted► High-resolution XPS of 5-methyltetrazole reveals different tautomers. ► 5MTZ exists mainly as 2H-5MTZ. ► ΔSCF results are in excellent agreement with the measured binding energies.The relative populations of the 1H- and 2H-tautomer of gas-phase 5-methyltetrazole (5MTZ) have been assessed through core-level photoelectron spectroscopy, and compared with the results obtained from Gaussian-n (Gn, n = 1, 2 and 3) and Complete Basis Set methods (CBS-4M and CBS-Q). The C 1s and N 1s core–electron binding energies (CEBEs) for each ionization site of both tautomers have been computed using the Δself-consistent-field (ΔSCF) approach. The C 1s and N 1s XPS spectra, obtained at 313 K, yield a 1H/2H tautomer ratio of ca. 0.16/0.84 and 0.21/0.79, respectively.
Computational characterization of the HOMO-2 photoemission intensity oscillations in C60 by Daniele Toffoli; Mauro Stener; Giovanna Fronzoni; Piero Decleva (154-157).
Display Omitted► Computational study of the HOMO-2 photoemission intensity oscillations in C60. ► DFT and TDDFT results are in excellent agreement with recent experimental data. ► An interpretation of the oscillations in the HOMO-2 cross section is provided.We have calculated the photoionization cross section of the HOMO, HOMO-1 and HOMO-2 photoemission bands of C60 from threshold up to 250 eV of photon energy. The calculated HOMO-2/HOMO-1 intensity ratio is in excellent agreement with recent experimental data. The computational method uses a multicentric expansion of the scattering wave function and a density functional theory (DFT) Hamiltonian. Time dependent DFT calculations suggest that the oscillatory phenomenon is essentially of single particle nature. An interpretation of the experimental findings in terms of the σ–π symmetries of the ionized orbitals is provided.
High-temperature and high-pressure thermal expansivity of cubic PtC from quasi-harmonic Debye model by Xiao-Wei Sun; Qi-Feng Chen; Ling-Cang Cai; Xiang-Rong Chen; Fu-Qian Jing (158-161).
The predicted thermal expansivity of cubic PtC at high temperatures and pressures using quasi-harmonic Debye model. It can be found that the volume thermal expansion coefficient α increases with temperature at all pressures for PtC with ZB structure, whereas the α decreases with increasing pressure and the effects of temperature become less and less pronounced resulting in linear high-temperature behavior for RS structure. This is mainly because the anharmonic effect becomes less important for high-pressure RS phase.Display Omitted► The thermal expansion coefficient α of cubic PtC is predicted for the first time. ► The α increases with temperature at all pressures for PtC in zinc-blende phase. ► The α is a weak function of temperature at high temperatures for PtC in rock-salt phase.The thermal expansivity of PtC with the rock-salt and zinc-blende structures under high pressures and temperatures are predicted by using first-principles density functional theory calculations combined with the quasi-harmonic Debye model. The effects of the pressures and temperatures on the P–V–T relationship and the volume thermal expansion coefficient α are successfully investigated for both two structures. It is found that the α increases with temperature at all pressures for zinc-blende phase and it is a weak function of temperature at high temperatures for rock-salt phase. The properties of cubic PtC are summarized in the pressure range of 0–100 GPa and the temperature up to 3000 K.
A chromophoric study of 2-ethylhexyl p-methoxycinnamate by Leonardo F. Alves; Ricardo Gargano; Silvia K.B. Alcanfor; Luiz A.S. Romeiro; João B.L. Martins (162-165).
Display Omitted► Octyl p-methoxycinnamate was theoretically and experimentally studied. ► TD-DFT methods including implicit solvent IEF-PCM model were used. ► Experimental absorption spectra were collected using ten different solvents.Ultraviolet absorption spectra of 2-ethylhexyl p-methoxycinnamate have been recorded in different solvents and calculated using the time dependent density functional theory. The calculations were performed with the aid of B3LYP, PBE1PBE, M06, and PBEPBE functionals and 6-31+G(2d) basis set. The geometries were initially optimized using PM5 semiempirical method for the conformational search. The calculations of excited states were carried out using the time dependent with IEF-PCM solvent reaction field method. The experimental data were obtained in the wavelength range from 200 to 400 nm using 10 different solvents. The TD-PBE1PBE method shows the best agreement to the experimental results.
Blue or red Δν XH complexation shift in X–H⋯CO2 hydrogen-bonded complexes? by Roman Szostak (166-170).
Display Omitted► The blue-shifting HB is characteristic for donors with a small positive charge on the H atom. ► These proton donors exhibit long and weak X–H bonds. ► As a rule, they form weak complexes with the CO2 molecule. ► The red-shifting HB occurs for molecules with greater positive charge on the H atom.The position of the ν(XH) stretching band for more than 100 proton donors (X = O, N, C, S, Se, P, Si, B, F, Cl, Br) complexed with CO2 was calculated at the MP2/6-311++G(d,p) level. Complexation energies and natural bond orbital characteristics were also determined. These calculations revealed that the direction of the ν(XH) band shift was related to the charge born by the hydrogen atom of the proton donor. X–H⋯O＝C＝O blue-shifting hydrogen bonds were found for compounds characterised by a small charge, while red-shifting was observed for those compounds with a high positive charge on the hydrogen atom.
Sum frequency generation study on the orientation of room-temperature ionic liquid at the graphene–ionic liquid interface by Steven Baldelli; Jiming Bao; Wei Wu; Shin-shem Pei (171-173).
Display Omitted► Vibrational spectra of monolayer on graphene. ► Solid–liquid interface. ► Ionic liquid orientation on graphene. ► Anion more strong interacting with graphene.The sum frequency generation (SFG) vibrational spectrum and contact angle of a room-temperature ionic liquid, 1-butyl-3-methylimidazolium methane sulfate, [BMIM][MS], at the graphene interface has been measured. The SFG spectra are dominated by the CH3 resonance of the anion. The methyl group of methane sulfate is oriented at an angle greater than 40° from the surface normal. The SFG data suggests the cation, [BMIM]+, is weakly oriented with the alkyl chain parallel to the graphene plane and the aromatic ring somewhat tilted from the surface plane. As the ionic liquid [BMIM][MS] wets the surface with a contact angle of 58 ± 2°, suggesting that the non-polar interaction of the alkyl chain and π–π interaction of the ring, to graphene dominate the surface interactions.
Nickel induced iono-covalent character of hydrogen in RbMgH3 from first principles by Adel F. Al Alam; Samir F. Matar; Naïm Ouaini (174-176).
Display Omitted► Selective substitutions of Mg by Ni in ionic hydride RbMgH3 are modeled within DFT. ► Change from ionic to iono-covalent behavior featured by the change of H−1 to H–0.2. ► This enables easier release of hydrogen with better kinetics for largest amount of Ni. ► RbMg1/3Ni2/3H3 proposed due to the large electropositive character of Rb in RbMgH3. ► Synthesis routes for such iono-covalent hydrides being explored with mechanosynthesis.The large ionic character in hexagonal perovskite RbMgH3 is reduced by selective substitutions by Ni followed by full geometry optimization within DFT leading to preserve the structure and symmetry of the pristine hydride. From the Bader charge analysis, an increasingly iono-covalent character is introduced with larger amounts of Ni substituting to Mg. For the Ni rich composition RbMg1/3Ni2/3H3, found most stable from cohesive energies, the charge on H decreases down to −0.2. This peculiar behavior should enable enhancing the kinetics of H release for potential applications.
Time-resolved laser-induced fluorescence spectroscopy of Nd3+ in molten LiCl–KCl eutectic by E.C. Jung; S.-E. Bae; Y.J. Park; K. Song (177-181).
Display Omitted► This Letter presents a study of the chemical speciation of Nd–chloride complexes in the molten LiCl–KCl eutectic. ► The laser-induced fluorescence spectra of Nd3+ are shown in the wavelength region of 360–900 nm. ► The coexistence of two different chemical species of Nd3+ in the high temperature molten salt is confirmed.The characteristics of the laser-induced fluorescence of Nd3+ in LiCl–KCl eutectic in the wavelength region of 360–900 nm were investigated for information concerning the chemical speciation of Nd-chloride complexes. When pumped at either 355 or 532 nm, Nd3+ in molten salt emits visible and near-IR fluorescence. The fluorescence peaks at 750 nm (4F7/2 + 4S3/2 → 4I9/2) and 810 nm (4F5/2 + 2H9/2 → 4I9/2) were particularly prominent at temperatures above the melting point. The fluorescence decay of these transition lines showed a bi-exponential behaviour of the fluorescence lifetime. These results provide evidence that two different chemical species of Nd3+ coexist in this system.
Evidence for bi-exponential decay of pyrene in condensed phase: Possibility of complex formation with solvent molecules by Partha Roy; Amit Kumar Jana; Subrata Das; Deb Narayan Nath (182-185).
Display Omitted► Bi-exponential decay of pyrene. ► Complex formation of Py∗ with solvent molecules. ► Attenuation of low frequency vibration modes in complexed pyrene.Lifetime of pyrene fluorescence has been measured in methanol and benzene–acetonitrile binary solvent of permittivity 15 along with the quenching effect by dimethylaniline (DMA) in these two solvents. In all cases pyrene fluorescence exhibits a bi-exponential decay. The data strongly points to the possibility of reversible complex formation of excited pyrene molecule with the solvent molecules (a few percent only) in addition to the existence of free excited pyrene molecules (majority). It has been observed that the fluorescence spectra of these two species differ significantly.
Nonlinear optical properties of lead nanocrystals embedding glass induced by thermal treatment and femtosecond laser irradiation by Geng Lin; Huaihai Pan; Jianrong Qiu; Quanzhong Zhao (186-191).
Display Omitted► Lead nanocrystals were precipitated inside borosilicate glass by thermal stimulation and femtosecond laser irradiation. ► Thermal treatment can precipitate lead nanocrystals inside whole glass. ► Femtosecond laser irradiation can fabricate lead nanocrystals within selective area of glass. ► The fabricated nanocrystals-glass composite exhibits large third-order optical nonlinearity and ultrafast response time. ► It is suitable for fabrication of ultrafast optical switches.We fabricated lead nanocrystals inside a specially designed borosilicate glass by two parallel approaches, thermal stimulation and femtosecond laser irradiation. Thermal treatment can precipitate lead nanocrystals inside whole glass, while femtosecond laser irradiation can induce lead nanocrystals within selective area of glass. The fabricated nanocomposite exhibits large third-order optical nonlinearity and ultrafast response time, which is suitable for fabrication of ultrafast optical switches. Furthermore, the femtosecond laser induced refractive index difference between lead crystalline and glass is about 0.13, which is enough to fabricate optical devices such as photonic crystals.
A low temperature in situ facile technique to enhance ultraviolet emission of zinc oxide nanorods and its mechanistic insights by S. Sarkar; D. Basak (192-198).
Growth of ZnO nanorods from zinc acetate salt in the presence of excess metallic zinc by hydrothermal method results in highly enhanced ultraviolet emission (I UV/I VIS ∼38). A strong electron paramagnetic resonance signal at g ∼1.95 for zinc-rich NRs together with the photoluminescence results confirms formation of higher concentration of paramagnetic zinc interstitial defects.Display Omitted► Hydrothermal growth of ZnO NRs from zinc acetate dihydrate in the presence of excess zinc. ► UV/VIS PL emission ratio of NRs grown with excess metal is enhanced to 38. ► UV/VIS PL emission ratio is enhanced seven times compared to that grown without excess zinc. ► EPR spectroscopy confirms formation of Zni defects in NRs grown with excess metal.A novel approach for enhancing the ultraviolet emission properties of ZnO nanorods (NRs) using a in situ facile hydrothermal technique in the presence of excess zinc metal in addition to zinc acetate in the precursor has been demonstrated. The photoluminescence studies show a higher ultra-violet (UV) emission (I UV/I VIS ∼38) in the NRs grown with 15 mM excess zinc metal compared to that (I UV/I VIS ∼5.5) of the NRs grown without excess metal. Electron paramagnetic resonance studies reveal a higher intensity signal at g ∼1.95 for NRs grown with 15 mM excess zinc indicating the presence of paramagnetic Zni in higher concentration.
Density functional theory prediction of geometry and vibrational circular dichroism of bridged triarylamine helicenes by Altaf Hussain Pandith; Nasarul Islam; Zeeshan Fatima Syed; Suhail-ul Rehman; Sateesh Bandaru; Anakuthil Anoop (199-203).
Display Omitted► We report the conformational preference and the VCD of bridged triarylamine helicenes. ► Helicenes in M configuration are more stable than helicenes in P-configuration. ► The two isomers show no significant dissimilarities in the IR absorptions. ► The VCD spectra of these molecules are good configuration markers. ► The calculated VCD spectra can be used for identification of absolute configuration. Ab initio calculations of conformational stabilities, IR absorption and vibrational circular dichroism spectra of four bridged triarylamine helicenes are reported, using DFT/B3LYP/6-31G(d, p) method. We find that the bridged triarylamine helicenes in M configuration are more stable than the helicenes in P-configuration (). The two atropisomers, M and P of the helicene 1 and 2 as well as the two diastereomers of the camphanate derivatives, 3 and 4, show no significant dissimilarities in the IR absorptions, but the VCD spectra of these molecules are the characteristic feature of the particular isomer and can be used for identification of absolute configuration of these chiral molecular systems, along with experimentally obtained VCD spectra.
Intriguing hybrid nanotubes with tunable structures by Li Li; Lijie Zhang; Jing Ren; Hui Zhang; Xuemei Sun; Houpu Li; Tao Chen; Huisheng Peng (204-207).
Novel hybrid nanomaterials with iron oxide nanoparticles incorporated in nitrogen-doped carbon nanotube have been synthesized with tunable structures by a ready chemical vapor deposition process. These hybrid nanotubes show promising electronic applications.Display Omitted► A novel hybrid nanotube has been synthesized by a chemical vapour deposition. ► The nanotubes exhibit tunable structures with remarkable electronic properties. ► Lithium ion battery, as an application example, is studied with high performance.Novel hybrid nanomaterials with iron oxide nanoparticles incorporated in nitrogen-doped carbon nanotube have been synthesized with tunable structures by a ready chemical vapor deposition process. These hybrid nanotubes show promising electronic applications.
Dipole polarizability, sum rules, mean excitation energies, and long-range dispersion coefficients for buckminsterfullerene C60 by Ashok Kumar; Ajit J. Thakkar (208-211).
Display Omitted► A dipole oscillator strength distribution for C60 is constructed. ► Dipole sum rules S k and mean excitation energies I k are obtained for C60. ► Long-range dispersion coefficients C 6 are computed for interactions of C60 with 54 other species.Experimental photoabsorption cross-sections combined with constraints provided by the Kuhn–Reiche–Thomas sum rule and the high-energy behavior of the dipole-oscillator-strength density are used to construct dipole oscillator strength distributions for buckminsterfullerene (C60). The distributions are used to predict dipole sum rules S k , mean excitation energies I k , the frequency dependent polarizability, and C 6 coefficients for the long-range dipole–dipole interactions of C60 with a variety of atoms and molecules.
Synthesis and characterization of nitrogen-doped monolayer and multilayer graphene on TEM copper grids by Gui-Ping Dai; Jian-Ming Zhang; Shuguang Deng (212-215).
Display Omitted► Single- and multi-layers nitrogen-doped graphene sheet on TEM copper grid. ► Chemical vapor deposition. ► Characterization with HRTEM, Raman, and XPS. ► Control of nitrogen atomic percentage in host graphene.Single- and multi-layer nitrogen-doped graphene was deposited on TEM copper grids by chemical vapor deposition from ammonia and methane. By controlling the gas mixture ratio the nitrogen atomic percentage in the host graphene can be regulated, ranging from 0.7% to 2.9%. High-resolution transmission electron microscopy and Raman spectroscopy reveal that high-quality nitrogen-doped single- and multi-layer graphene sheets were obtained. The existence of nitrogen substitution in the graphene lattices is confirmed by X-ray photoelectron spectroscopy.
Molecular simulations of the competitive adsorption of siloxanes and water on amorphous silica surfaces as a function of temperature by Joachim K. Floess; Sohail Murad (216-219).
Molecular simulations of water and PDMS on silica surface show that the presence of water significantly affects the adsorption of PDMS but the presence of PDMS does not affect the adsorption of water. In addition the adsorption of silica is very sensitive to the nature of the silica surface but water adsorption is relatively unaffected by small changes.Display Omitted► The adsorption of PDMS is sensitive to small changes in surface characteristics. ► Vapor pressure is enhanced at low temperatures and depressed at high temperatures. ► The adsorption of water on silica is not affected much by the presence of PDMS. ► However, the adsorption of PDMS on silica is affected by the presence of water.Molecular simulations of individual and competitive adsorption of water and PDMS (polydimethylsiloxane) on an amorphous silica surface in the temperature range 300–1500 K show that the presence of PDMS does not appear to change the adsorption behavior of water significantly but that the presence of water has a substantial effect on the adsorption behavior of PDMS at temperatures below approximately 600 K. Water adsorbs adjacent to and penetrates into the silica surface while PDMS adsorbs adjacent to the water layer. Finally, the vapor pressure is enhanced at low temperatures because of the formation of nanoclusters on the surface as a consequence of the Gibbs–Thomson effect.
A joint Raman and EPR spectroscopic study on ball-milled nanographites by M. Tommasini; C. Castiglioni; G. Zerbi; A. Barbon; M. Brustolon (220-224).
Display Omitted► Graphite ball milled at increasing times for tuning crystallite size. ► Raman, EPR and SEM characterization. ► Found correlation between Raman and EPR signals.Multi-wavelength Raman and EPR spectroscopies have been used on ball-milled graphite to investigate the effect of varying crystallite size and defect concentration. A correlation between Raman I D/I G intensity ratio and EPR T 1 spin lattice relaxation time of conduction electrons has been discovered which could represent an appealing characterization technique for graphitic materials.
Dependence of transport property of graphene nanoribbon on contacts: Electron–hole symmetry and conductance at the Dirac point by G.P. Zhang; Z.J. Qin (225-229).
Display Omitted► We confirm general predictions for the transport through graphene nanoribbon (GNR) for specific geometries. ► Electron–hole symmetry depends sensitively on the structure of contact and GNR/contact interface. ► Electron–hole symmetry breaks in armchair graphene nanoribbon (AGNR) in the presence of odd-numbered ring at the interface. ► The unique momentum for maximal transmission is determined by the scattering between quantum wire and AGNR. ► The conductance at Dirac point is independent of the structure of contact with dense modes around Dirac point.Our investigation of the transport properties in graphene nanoribbon’s (GNR) between quantum wire contact and decoupled chains contact confirms general predictions for the transport through GNR for specific geometries. We found that electron–hole (e–h) symmetry depends sensitively on the contact and interface. For quantum wire contacts, the breaking of e–h symmetry occurs in armchair GNR due to odd-numbered ring at the interface, and at Dirac point the maximal transmission corresponds to the momentum k y = 2 π 3 3 a (a = 0.142 Å). The spatial density of states of armchair GNR is shown. Furthermore, the conductance at Dirac point is independent of contacts with dense modes.
Hydrogen-doped cubic diamond and the crystal structure of n-diamond by Bin Wen; Roderick Melnik; Shan Yao; Tingju Li (230-232).
Hydrogen dependent mechanical stability for H-doped diamond.Display Omitted► A novel hydrogen doped diamond structure, has been built. ► Structural stability of hydrogen doped diamond has been studied. ► n-Diamond is likely to be an hydrogen doped diamond.A comprehensive analysis of the crystal structure of n-diamond has been carried out based on a hydrogen-doped (H-doped) diamond model using first principles calculations. In particular, hydrogen concentration dependent elastic constants and lattice parameters for the H-doped diamond have been analyzed. Our results indicate that when the hydrogen concentration is less than 19 at.%, the H-doped diamond is mechanically stable. When the hydrogen concentration is about 4 at.%, the optimized lattice parameter, simulated XRD pattern and electronic properties for the H-doped diamond are all agree well with the corresponding experimental values of n-diamond. The results imply that the n-diamond is likely to be an H-doped diamond.
A mechanism of catalyzed GTP hydrolysis by Ras protein through magnesium ion by Qiang Lu; Nicolas Nassar; Jin Wang (233-238).
Display Omitted► GTPase. ► Ras hydrolysis. ► GTP. ► Magnesium. ► Umbrella sampling. ► Minimum energy path.The hydrolysis by Ras plays pivotal roles in the activation of signaling pathways that lead to cell growth, proliferation, and differentiation. Despite their significant role in human cancer, the hydrolysis mechanism remains unclear. In the present Letter, we propose a GTP hydrolysis mechanism in which the γ phosphate is cut off primarily by magnesium ion. We studied both normal and mutated Ras and the cause of the malfunction of these mutants, compared the effect of Mg2+ and Mn2+. The simulation results are consistent with the experiments and support the new hydrolysis mechanism. This work will benefit both GTPases and ATPases hydrolysis studies.
On the inhibition of AHAS by chlorimuron ethyl: A theoretical study by Gonzalo A. Jaña; Joel B. Alderete; Eduardo J. Delgado (239-243).
Display Omitted► The inhibition of AHAS is addressed with the tools of computational chemistry. ► It is hypothesized the inhibition proceeds via a nucleophilic aromatic reaction. ► The obtained results agree with the empirical evidence for the inhibition process.The reaction between chlorimuron ethyl (CE) herbicide and the HEThDP− intermediate is addressed with the tools of computational chemistry, molecular dynamics and quantum chemistry, in order to check the postulated hypothesis that the inhibition of AHAS could proceed via a nucleophilic aromatic substitution reaction between HEThDP− and chlorimuron ethyl. The obtained results agree well with the empirical evidence for the inhibition process of AHAS by sulfonylureas, supporting the idea that the inhibition process could proceed by this via. It is also found that the nucleophilic attack of the Cα of the intermediate on the ipso carbon of the herbicide pyrimidinic ring is the rate-limiting step.
Investigation of hydrogen bond in binary mixture (pyridine + propionic acid) by spectroscopy and DFT calculations by Yuan-Zheng Chen; Tian-Yuan Liu; Guan-Nan Qu; Shang Sun; Shu-Qin Gao; Mi Zhou; Chen-Lin Sun; Zuo-Wei Li (244-249).
Display Omitted► Model of Electronic Behavior interpreted the blue shift of the ring breathing mode. ► The line shape of pyridine’s ring breathing and triangle mode were discussed. ► We optimized the hydrogen-bonded clusters by DFT and obtained the spectral features. ► We discussed the effect of the hydrogen bond on Fermi Resonance.This Letter analyzed the hydrogen bond between pyridine and propionic acid using Raman and infrared spectra as a function of concentrations. The wavenumber shift and line width change were investigated to analyze the effects of hydrogen bond on the ring breathing mode and the triangle mode of pyridine. Density functional theory (DFT) at the B3LYP/6-31++G (d,p) level was performed on the binary solution. The simulated vibrational Raman spectra obtained the experimentally observed spectral features about the blue-shifted of the ring breathing mode. Furthermore, the effect of the hydrogen bond on Fermi Resonance (FR) was discussed.
Explicit solvent effects on the visible absorption spectrum of a photosynthetic pigment: Chlorophyll-c2 in methanol by Paula Jaramillo; Kaline Coutinho; Benedito J.C. Cabral; Sylvio Canuto (250-253).
Display Omitted► Inclusion of explicit solvent effects on the spectrum of a photosynthetic pigment. ► An accurate description of the intense Soret and the low-lying Q states. ► The Soret band cannot be entirely understood within the 4-orbital model. ► Analysis of the existence and the proper location of the dark states in solvent. ► Solute–solvent hydrogen bonds has influence in the visible spectrum.The explicit solvent effects on the light absorption properties of a photosynthetic pigment are analyzed from a combined study using Monte Carlo simulation and quantum mechanical Density-Functional Theory calculations. The case considered is chlorophyll-c2 in methanol and excellent results are obtained for both position and intensities in the entire visible region. Explicit solvent molecules are essential for describing the absorption spectrum. Analysis is also made of the coordination of the Mg atom, the influence of solute–solvent hydrogen bonds, the existence and location of dark states for internal conversion mechanisms and the adequacy of the four-state model for classifying the transitions.
Probing electric field in double-layer electroluminescence diode by optical second harmonic generation by Eunju Lim; Takaaki Manaka; Mitsumasa Iwamoto (254-256).
Display Omitted► EFISHG was employed to probe the electric field in IZO/α-NPD/Alq3/Al diode. ► EFISHG was generated from α-NPD and Alq3 layers at different wavelength. ► EFISHG is an effective way to probe the electric field distribution in EL diodes.Optical second harmonic generation (SHG) measurement has been employed for studying electric field distribution in organic double-layer electroluminescence diode. Taking advantage of the material dependence on the SHG, we measured the electric field induced SHG (EFISHG) from IZO/α-NPD/Alq3/Al diode. The generated SH signal wavelength was governed by the active organic layers, and two peaks were generated at 940 nm from the α-NPD and at 1050 nm from the Alq3 layers. The SHG intensity was dependent on applied d.c. voltages, but the voltage dependence was totally opposite between the two peaks. Interface carrier charging caused by the Maxwell–Wagner effect accounted for the results. We concluded that the EFISHG provides an effective way to probe the electric field distribution in double-layer electroluminescence diodes.
Light yield and energy transfer in a new Gd-loaded liquid scintillator by C. Aberle; C. Buck; F.X. Hartmann; S. Schönert (257-262).
Display Omitted► An energy transfer paths model for metal loaded liquid scintillators is developed. ► Light yield measurements to determine the transfer rate parameters of the model. ► The Double Chooz scintillator components concentrations are optimized.We investigate a new gadolinium-loaded organic liquid scintillator which is designed to detect electron antineutrinos. A model has been developed to account for the various energy transfer paths possible in a liquid scintillator with multiple solvents, one fluor and a quenching component. Experimental light yield measurements were carried out to determine the relative rates for the energy transfers included in the model. Model predictions were used to tune the luminescent properties of the Gd-loaded target scintillator and the unloaded Gamma Catcher scintillator for the reactor neutrino experiment Double Chooz.
Temporal quantum mechanics/molecular mechanics: Extending the time scales accessible in molecular dynamics simulations of reactions by Prakash Dayal; Sabine A. Weyand; Joanne McNeish; Nicholas J. Mosey (263-267).
Display Omitted► A novel approach to extend the time scales accessible in simulations of reactions. ► The approach combines force-fields, semi-empirical molecular orbital and quantum chemical methods. ► Access to long time scales without artificially accelerating the dynamics. ► Extends accessible time scales by several orders of magnitude and captures reactive events.An approach termed temporal quantum mechanics/molecular mechanics is presented to extend the time scales accessible in molecular dynamics simulations of reactions. This approach employs a hierarchy of methods: force-fields (FFs) to simulate the system near potential energy minima, semi-empirical (SE) molecular orbital methods to assess the likelihood of trajectories overcoming reaction barriers, and quantum chemical (QC) methods to model changes in bonding and electronic structure during reactions. This method relies primarily on FFs and SE methods, providing access to much longer time scales than those accessible using QC methods alone, with the targeted use of QC methods ensuring reactive events are described properly.
Electron localization in nonplanar conjugated macrocycles: Failure of electron buffers to delocalize electrons by Yang Yang (268-271).
Display Omitted► Radical generated by homolysis of the axial metal–ligand bond in a macrocycle. ► Electron delocalization through the conjugated ring contributes to the stability. ► Descriptors about the distribution of the unpaired electron in the radical. ► Competition of electron doping sites: metal-centered versus macrocycle-centered. ► Redox chemistry and electron transfer are affected by planarity.We investigate the distribution of the unpaired electron generated by the homolysis of the axial metal–ligand bond in some aromatic metallomacrocycles. For one group of the compounds, the unpaired electron is delocalized in the conjugated ring. This is an expected feature for planar macrocycles. Consequently, the conjugated ring is significantly affected. In contrast, the unpaired electron localizes around the central metal and leaves the aromatic ring almost unaffected in the other group of the compounds. These two different distribution patterns are revealed by different structural features, spin densities, electron localization functions (ELF), and nucleus-independent chemical shifts (NICS).
Statistical properties of blinking kinetics in single molecule by Yonggang Peng; Yujun Zheng (272-276).
The probabilities of the system in the ON state (upper) and OFF state (lower) after the system undergoes serval times between ON and OFF states with the system initial in the OFF states, | off > ( t 0 ) = σ off 1 ( t 0 ) | off 1 > + σ off 2 ( t 0 ) | off 2 > , the dashed-dot line corresponds to the σ on ( 1 ) , the dashed line corresponds to the σ on ( 3 ) and the solid line corresponds to the σ on ( 5 ) (upper). The dashed-dot line corresponds to the σ off ( 0 ) , the dashed line corresponds to the σ off ( 2 ) and the solid line corresponds to the σ off ( 4 ) . The red lines correspond to the OFF1 state’s contribution to the ON distribution, the blue lines correspond to the OFF2 state’s contribution to the ON distribution (lower).Display Omitted► We extend the generating function theory to the blinking kinetics of single molecule. ► The waiting time distributions, high order cumulants etc. are investigated. ► This can used to study ‘large-deviation’ and the non-equilibrium ‘counting’ fields.We study the statistical properties of blinking kinetics of single terrylene molecule in p-terphenyl crystal with intersystem crossing process (ISC) via generating function. The analytical expression of the waiting time distribution of the ‘bright’ and ‘dark’ period is obtained, which demonstrates that the behaviors of the ‘dark’ period show bi-exponential decaying because of two kinds of sublevels. The probability of the single terrylene molecule in the ‘bright’ and ‘dark’ states are also investigated. Our theoretical results are in good agreement with experimental results.
Author Index (277-281).