Electron Momentum Spectroscopy of Outer Valence Orbitals of 2-Fluoroethanol

The binding energy spectra and electron momentum distributions for the outer valence molecular orbitals of gaseous 2-fluoroethanol have been measured by the non-coplanar asym- metric （e, 2e） spectrometer at impact energy of 2.5 keV plus binding energy. The quantitative calculations of the ionization energies and the relevant molecular orbitals have been carried out by using the outer-valence Green＇s function method and the density functional theory with B3LYP hybrid functional. The observed ionization bands in binding energy spectra, as well as the previous photoelectron spectrum which was not assigned, have been assigned for the first time through the comparison between experiment and theory. In general, the the- oretical electron momentum distributions calculated by B3LYP method with aug-cc-pVTZ basis set are in line with the experimental ones when taking into account the Boltzmann- weighted thermo-statistical abundances of five conformers of 2-fluoroethanol.

Experimental and Theoretical Study of Deprotonation of DNA Adenine Cation Radical

Among all the DNA components, extremely redox-active guanine （G） and adenine （A） bases are subject to facile loss of an electron and form cation radicals （G＋＂ and A＋＇） when exposed to irradiation or radical oxidants. The subsequent deprotonation of G＋＇ and A＋＇ can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G＋, studies on the deprotonation of A＋ are still limited at present. Herein, we investigate the deprotonation behavior of A＋. by time-resolved laser flash photolysis. The deprotonation product of A（N6-H）＇ is observed and the deprotonation rate constant, （2.0±0.1）×10 7 s-1, is obtained at room temperature. Further, the deprotonation rate con- stants of A＋. are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N6-H deprotonation is determined to be （17.1±1.0） kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A＋ deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A＋ in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.

Time-dependent Density Functional-based Tight-bind Method Efficiently Implemented with OpenMP Parallel and GPU Acceleration

The time-dependent density functional-based tight-bind （TD-DFTB） method is implemented on the multi-core and the graphical processing unit （GPU） system for excited state calcu-lations of large system with hundreds or thousands of atoms. Sparse matrix and OpenMP multithreaded are used for building the Hamiltonian matrix. The diagonal of the eigenvalue problem in the ground state is implemented on the GPUs with double precision. The GPU- based acceleration fully preserves all the properties, and a considerable total speedup of 8.73 can be achieved. A Krylov-space-based algorithm with the OpenMP parallel and CPU acceleration is used for finding the lowest eigenvalue and eigenvector of the large TDDFT matrix, which greatly reduces the iterations taken and the time spent on the excited states eigenvalue problem. The Krylov solver with the GPU acceleration of matrix-vector product can converge quickly to obtain the final result and a notable speed-up of 206 times can be observed for system size of 812 atoms. The calculations on serials of small and large systems show that the fast TD-DFTB code can obtain reasonable result with a much cheaper computational requirement compared with the first-principle results of CIS and full TDDFT calculation.

Syntheses and calculation of( E)-4-chloro-4'-ethoxystilbene and( E)-4,4'-dichlorostilbene

（E） -4-chloro-4＇ -ethoxystilbene （2a） and （E） -4, 4＇ - dichlorostilbene （2b） were synthesized by the Witting-Homer reaction. The crystals of 2a and 2b were prepared through solvent evaporation and characterized by the single-crystal X- ray diffraction. Molecular structure analysis confirms the E- configuration of C=C bond. The crystal of 2a reveals an orthorhombic and space group Pna21 structure while 2b shows a monoclinic and space group P21/c structure. The electronic structures of 2a and 2b were optimized at B3LYP/6-311 ＋ ＋ G （d, p） level. The Hirshfeld surface and fingerprint plot indicate close O-H and C1-H contacts and π-π stacking in 2a and 2b. Molecular electrostatic potential shows that the O and C1 atoms of 2a and C1 atoms of 2b have the minimum energies and they are more likely to be attacked by electrophiles in reaction. Frontier molecular orbitals analysis demonstrates that the △ELuMO_HOMO of 2a and 2b are 3.85 and 3.91 eV, respectively.

High Resolution Electron Momentum Spectroscopy Study on Ethanol： Orbital Electron Momentum Distributions for Individual Conformers

The outer-valence binding energy spectra of ethanol in the energy range of 9-21 eV are mea- sured by a high-resolution electron momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The electron momentum distributions for the ionization peaks cor- responding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calcu- lations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured electron momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical electron momentum distributions for the molecular orbitals of individual conformers （i.e., 8a＇ of trans and 9a of gauche）, but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution electron momentum spectrometer, by inspecting the molecular electronic structure, is a promising technique to identify different conformers in a mixed sample.

Theoretical Studies on the Ground State and Excited State of 2,7′- （Ethylene）-bis-8-hydroxyquinoline

2,7′-（Ethylene）-bis-8-hydroxyquinoline was optimized with DFT/B3LYP and ab initio HF methods, so ion- ization potential and electron affinity could be determined. Absorption spectrum was calculated by ZINDO and TD-DFT. CIS method was used to calculate the S1 excited states of the compound and afterwards the emission spectrum was computed. When the solvent effect was taken into account, the computed results show encouraging agreement with known experimental data. The results of analyzing the relationship between the energies and absorption spectra indicate that the ability to transporting electrons is strengthened compared with 8-hydroxyquinoline and that absorption and emission spectra are red-shifted. The intramoleeular reor- ganization energy of tris（2,7′-（ethylene）-bis-8-hydroxyquinoline）-aluminum implies its electron transporting property is worse than tris（8-hydroxyquinoline）-aluminum. The predicted maximum emission wavelength is red-shifted compared with tris（8-hydroxyquinoline）-aluminum.

Eu Ions Site-selective Doping and Nonstoichiometric Chemistry of NaTaO3 in Na-rich Environment

The electronic structure of Eu-doped NaTaO3 in Na-rich environment is investigated by the first-principles theory. By simulating the two different models of Eu3＋ ions selectively located in Ta and Na sites, respectively, the band gaps of two Eu-doped NaTaO3 models were all narrowed, which were assigned to lattice defects and impurity band of the Eu dopent. For the model of Eu3＋ ions located in the Na＋ sites of NaTaO3, the new impurity band mainly composited of Eu 4f orbital appeared at the top over the valence band, indicating the enhanced oxidative ability. For the model of Eu3＋ ions located in the Ta5＋ sites of NaTaO3, a midgap state generated was located at the bottom of conduct band and the band potential shifted up, confirming the strong reductive ability in the Na-rich enviornment. The densities of electron states were significantly increased in both the conduction and valence bands in Na-rich model, which resulted in the increased carrier migration rate and thus photocatalytic activity enhancement. It is proposed that Eu3＋ ions doping at the Ta sites could enhance the reduced photocatalytic performance via controlling the nonstoichiometric Na/Ta molar ratio in the Eu-doped NaTaO3 system.

Hydrogen Bonding Effects on the Photophysical Properties of 2,3-dihydro-3-keto- 1H-pyrido[3,2,1-kl] phenothiazine

Time-dependent density functional theory （TDDFT） and femtosecond transient absorption spectroscopy were used to investigate the photophysical properties of 2,3-dihydro-3-keto-lH- pyrido[3,2,1-kl]phenothiazine （PTZ4） and 3-keto-lH-pyrido[3,2,1-kl]phenothiazine （PTZ5）. The calculated results obtained from TDDFT suggest that the red-shifts of the absorption spectra of these two fluorophores in methanol are due to the formation of hydrogen-bonded complexes at the ground state. Four conformers of PTZ4 were obtained by TDDFT. The two fluorescence peaks of PTZ4 in tetrahydrofuran （THF） came from the ICT states of the four conformers. The fluorescence of PTZ4 in THF showed a dependence on the excitation wavelength because of butterfly bending. The excited state dynamics of PTZ4 in THF and methanol were obtained by transient absorption spectroscopy. The lifetime of the excited PTZ4 in methanol was 53.8 ps, and its relaxation from the LE state to the ICT state was completed within several picoseconds. The short lifetime of excited PTZ4 in methanol was due to the formation of out-of-plane model hydrogen bonds between PTZ4 and methanol at the excited state.

Density Functional Theory Investigation on the Second-Order Nonlinear Optical Properties of Chlorobenzyl-o-Carborane Derivatives

The structures and second-order nonlinear optical （NLO） properties of a series of chlorobenzyl-o-carboranes derivatives （1 12） containing different push-pull groups have been studied by density functional theory （DFT） cal- culation. Our theoretical calculations show that the static first hyperpolarizability （fltot） values gradually increase with increasing the π-conjugation length and the strength of electron donor group. Especially, compound 12 exhibits the largest βtot （62.404 × 10^-30 esu） by introducing tetrathiafulvalene （TTF）, which is about 76 times larger than that of compound 1 containing aryl. This means that the appropriate structural modification can substantially increase the first hyperpolarizabilities of the studied compounds. For the sake of understanding the origin of these large NLO responses, the frontier molecular orbitals （FMOs）, electron density difference maps （EDDMs）, orbital energy and electronic transition energy of the studied compounds are analyzed. According to the two-state model, the lower transition energy plays an important role in increasing the first hyperpolarizability values. This study may evoke possible ways to design preferable NLO materials.

Theoretical study on the application of the largest aluminum-pyrazole ring in electrochemical nitrogen reduction reaction

Electrochemical nitrogen reduction reaction(NRR)is a mild and sustainable method for ammonia synthesis.Therefore,developing high activity,selectivity,and economic efficiency catalysts with considering the synergistic effects between catalysts and carriers to design novel structural models is very important.Considering the non-noble metal NRR catalyst,Mo3,we tried to find a suitable carrier which is stable and economical.Herein,we used the largest atomically precise aluminum-pyrazole ring(AlOC-69)to date(diameter up to 2.3 nm).The larger ring cavities and the presence of abundant hydroxy groups make AlOC-69 an ideal molecular carrier model and provide a basis for studying its structure-activity relationship.The formation energy(-0.76eV)and stable Mo-0 bonds indicate that Mo_(3)can be stabilized on the Al_(10)O_(10)surface.Additionally,N_(2)has fully activated due to the strong interaction between the p-orbital of N and the d-orbital of Mo.The low limiting potential(-0.28V)emerges that Mo_(3)@Al_(10)O_(10)has ideal catalytic activity and selectivity.This research provides a promising catalyst model and an understanding of its catalytic process at the atomic level,providing a new approach for the co-design of catalyst and carrierin NRR.

ADSORPTION OF TiCl_4 AND ELECTRON DONOR ON DEFECTIVE MgCl_2 SURFACES AND PROPYLENE POLYMERIZATION OVER ZIEGLER-NATTA CATALYST: A DFT STUDY

The formations of defective MgC12 surfaces, and subsequent adsorption of Ti species and electron donor, as well as propylene polymerization over the Ziegler-Natta catalyst have been investigated using density functional theory （DFT） method. Twelve possible support models of regular and defective MgC12 （110） and （100） surfaces were built. The individual adsorptions of titanium chlorides as mononuclear or dinuclear, and ethyl benzoate （EB） as electron donor, on these models were evaluated. The analysis of energies presented the cases of EB adsorption were generally more stable than titanium chlorides on both surfaces. Thus, EB as internal electron donor mainly prevented TIC14 from coordinating on the MgC12 surfaces where mostly non-stereospecific active sites could be formed. Exceptionally, A5 the site model with terminal Cl-vacancy on the MgC12 support, presented stronger adsorption of TiCl4 than that of EB on （110） surface. Since the TIC14 and ethyl benzoate （EB） would compete to adsorb on the support surface, it seems reasonable to assume that TIC14 might predominately occupy this site, which can act as the most plausible active site for propylene polymerization. The first insertion of propylene monomer into the A5 active site model showed that it exhibited good regioselectivity but poor stereospecificity in the absence of electron donor.

Review of the first principles calculations and the design of cathode materials for Li-ion batteries

Cathode materials are the most critical chal- lenge for the large scale application of Li-ion batteries in electric vehicles and for the storages of electricity. The first principles calculations play an important role in develop- ment and optimization of novel cathode materials. In this paper, we overview the first principles calculations of energy, volume change, band-gap, phase diagram, and Li- ion transport mechanism of cathode materials with an emphasis on the design of such materials. We also over- view the recent progress of data mining techniques and the high-throughput first principles calculations for the design and development of cathode materials. Finally, we preview the challenges and opportunities of this rapidly developing field.