Density Functional Study of the C Atom Adsorption on the α-Fe_2O_3 (001) Surface

The adsorption of C atoms on the α-Fe2O3（001） surface was studied based on density function theory（DFT） ,in which the exchange-correlation potential was chosen as the PBE（Perdew,Burke and Ernzerhof） generalized gradient approximation（GGA） with a plane wave basis set. Upon the optimization on different adsorption sites with coverage of 1/20 and 1/5 ML,it was found that the adsorption of C atoms on the α-Fe2O3（001） surface was chemical adsorption. The coverage can affect the adsorption behavior greatly. Under low coverage,the most stable adsorption geometry lied on the bridged site with the adsorption energy of about 3.22 eV; however,under high coverage,it located at the top site with the energy change of 8.79 eV. Strong chemical reaction has occurred between the C and O atoms at this site. The density of states and population analysis showed that the s,p orbitals of C and p orbital of O give the most contribution to the adsorption bonding. During the adsorption process,O atom shares the electrons with C,and C can only affect the outermost and subsurface layers of α-Fe2O3; the third layer can not be affected obviously.

Oxygen Atom Transfer Reaction of Manganese-oxo Corrole toward Dimethyl Sulfide: a Density Functional Study

The effects of axial ligand on the oxygen atom transfer(OAT)reaction from 5,10,15-tris(pentafluorophenyl)corrole((tpfc)MnVO)to dimethyl sulfide(DMS)have been investigated by density functional theory(DFT)calculations.Imidazole(Im),4-methylimidazole(4-MI)and pyridine(Py)were selected as the axial ligands.The results revealed that the axial ligand can form coordinate bond with(tpfc)MnVO in the transition state(TS)of the OAT reaction.The axial coordination favored charge transferring from(tpfc)MnVO to DMS,and weakened the Mn≡O bond in both singlet and triplet states.Furthermore,axial coordination can reduce the energy barrier of neutral(tpfc)MnVO from 23.62 kJ·mol^-1 to less than 3 kJ·mol^-1 in the triplet state,which is significantly lower than in the singlet state.This makes(tpfc)MnVO tend to direct the OAT reaction via triplet state pathway.On the other hand,the energy barriers of[(tpfc)MnVIO]+species from disproportionation pathway increased from 1.26 to 33.95 kJ·mol^-1 in a doublet state.This suggests axial ligands were conducive for direct(tpfc)MnVO OAT reaction pathway.

Transition‐metal‐atom‐pairs deposited on g‐CN monolayer for nitrogen reduction reaction:Density functional theory calculations

The development of highly active DFT catalysts for an electrocatalytic N_(2)reduction reaction(NRR)under mild conditions is a difficult challenge.In this study,a series of atom‐pair catalysts(APCs)for an NRR were fabricated using transition‐metal(TM)atoms(TM=Sc−Zn)doped into g‐CN monolayers.The electrochemical mechanism of APCs for an NRR has been reported by well‐defined density functional theory calculations.The calculated limiting potentials were−0.47 and−0.78 V for the Fe_(2)@CN and Co_(2)@CN catalysts,respectively.Owing to its high suppression of hydrogen evolution reactions,Co_(2)@CN is a superior electrocatalytic material for a N_(2)fixation.Stable Fe_(2)@CN may be a strongly attractive material for an NRR with a relatively low overpotential after an improvement in the selectivity.The two‐way charge transfer affirmed the donation‐acceptance procedure between N_(2)and Fe_(2)@CN or Co_(2)@CN,which play a crucial role in the activation of inert N≡N bonds.This study provides an in‐depth investigation into atom‐pair catalysts and will open up new avenues for highly efficient g‐CN‐based nanostructures for an NRR.

A Method of Inversing the Peak Density of Atomic Oxygen Vertical Distribution in the MLT Region From the OI (557.7 nm)Night Airglow Intensity

In this paper, using the MSISE-90 model as the reference atmosphere, we discuss the feasibility and method of deducing the peak densities of the undisturbed atomic oxygen profiles in the MLT region (the mesosphere and lower thermosphere region) from OI (557.7 nm) night airglow intersities. The peak densities for different seasons, latitudes and longitudes are deduced from OI (557.7nm) airglow intensities through this expression. We analyze the features of inversion relative errors and discuss the influence of the variations in temperature on inversion errors. The results indicate that all inversion errors are less than 5% except for those at high altitudes in the summer hemisphere. And the impact of the variations in temperature on errors is not significant.

Revision of single atom local density and capture number varying with coverage in uniform depletion approximation and its effect on coalescence and number of stable clusters

In vapour deposition, single atoms （adatoms） on the substrate surface are the main source of growth. The change in its density plays a decisive role in the growth of thin films and quantum size islands. In the nucleation and cluster coalescence stages of vapour deposition, the growth of stable clusters occurs on the substrate surface covered by stable clusters. Nucleation occurs in the non-covered part, while the total area covered by stable clusters on the substrate surface will gradually increase. Carefully taking into account the coverage effect, a revised single atom density rate equation is given for the famous and widely used thin-film rate equation theory, but the work of solving the revised equation has not been done. In this paper, we solve the equation and obtain the single-atom density and capture number by using a uniform depletion approximation. We determine that the single atom density is much lower than that evaluated from the single atom density rate equation in the traditional rate equation theory when the stable cluster coverage fraction is large, and it goes down very fast with an increase in the coverage fraction. The revised equation gives a higher value for the ＇average＇ capture number than the present equation. It also increases with increasing coverage. That makes the preparation of single crystalline thin film materials difficult and the size control of quantum size islands complicated. We also discuss the effect of the revision on coalescence and the number of stable clusters in vapour deposition.

Determination of the atomic density of rubidium-87

Atomic density is a basic and important parameter in quantum optics, nonlinear optics, and precision measurement.In the past few decades, several methods have been used to measure atomic density, such as thermionic effect, optical absorption, and resonance fluorescence. The main error of these experiments stemmed from depopulation of the energy level, self-absorption, and the broad bandwidth of the laser. Here we demonstrate the atomic density of^87 Rb vapor in paraffin coated cell between 297 K and 334 K mainly using fluorescence measurement. Optical pumping, anti-relaxation coating, and absorption compensation approaches are used to decrease measurement error. These measurement methods are suitable for vapor temperature at dozens of degrees. The fitting function for the experimental data of87 Rb atomic density is given.

A NEW FORMULA FOR CALCULATING THE DENSITY OF METALS FROM THEIR ATOMIC STRUCUTURE PARAMETERS

Bused on the consideration o (?) mass and volume of one atom, a new formula tor calculating the density of simple metal substance from their atomic structure parameters is established. The densities of 66 metals in the periodic table were calculated from this formula. The calculated results are in agreement with the measured values reported in literature. The advantage of the present formula over the others is brie fly discussed.

Using density functional calculations to elucidate atomic ordering of Pd-Rh nanoparticles at sizes relevant for catalytic applications

Pd-Rh nanoparticles are known to easily undergo surface restructuring in reactive environment. This study quantifies, with the help of density functional(DFT) calculations and a novel topological approach, atomic ordering and surface segregation effects in Pd-Rh particles with compositions 1:3, 1:1 and 3:1 containing up to 201 atoms(ca. 1.7 nm). The obtained data are used to reliably optimise energetically preferred atomic orderings in inaccessible by DFT Pd-Rh particles containing thousands of atoms and exhibiting sizes exceeding 5 nm, which are typical for catalytic metal particles. It is outlined, how segregation effects on the surface arrangement of Pd-Rh nanoalloy catalysts induced by adsorbates can be evaluated in a simple way within the present modelling setup.

Catalytic activity of V_(2)CO_(2) MXene supported transition metal single atoms for oxygen reduction and hydrogen oxidation reactions:A density functional theory calculation study

Two-dimensional(2D)MXene and single-atom(SA)catalysts are two frontier research fields in catalysis.2D materials with unique geometric and electronic structures can modulate the catalytic performance of supported SAs,which,in turn,affect the intrinsic activity of 2D materials.Density functional theory calculations were used to systematically explore the potential of O-terminated V2C MXene(V_(2)CO_(2))-supported transition metal(TM)SAs,including a series of 3d,4d,and 5d metals,as oxygen reduction reaction(ORR)and hydrogen oxidation reaction(HOR)catalysts.The combination of TM SAs and V_(2)CO_(2)changes their electronic structure and enriches the active sites,and consequently regulates the intermediate adsorption energy and catalytic activity for ORR and HOR.Among the investigated TM-V_(2)CO_(2)models,Sc-,Mn-,Rh-,and PtMCCh showed high ORR activity,while Sc-,Ti-,V-,Cr-,and Mn-V_(2)CO_(2)exhibited high HOR activity.Specifically,Mn-and Sc-V_(2)CO_(2)are expected to serve as highly efficient and cost-effective bifunctional catalysts for fuel cells because of their high catalytic activity and stability.This work provides theoretical guidance for the rational design of efficient ORR and HOR bifunctional catalysts.

Measurements of Absolute Atomic Nitrogen Density by Two-Photon Absorption Laser-Induced Fluorescence Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

For the first time, absolute densities of atomic nitrogen in its ground state (N4S) have been measured in hot dry and humid air plasma columns under post-discharge regime. The determination of space-resolved absolute densities leads to obtain the dissociation degrees of molecular nitrogen in the plasma. The hot plasmas are generated inside an upstream gas-conditioning cell at 600 mbar when the air gas flow is directly injected at 10 slm in a microwave resonant cavity (2.45 GHz, 1 kW) placed in the downstream side. Density measurements based on laser induced fluorescence spectroscopy with two-photon excitation (TALIF), are more particularly performed along the radial and axial positions of the plasma column. Calibration of TALIF signals is performed in situ (i.e. in the same gas-conditioning cell but without plasma) using an air gas mixture containing krypton. Optical emission spectroscopy is considered to estimate the rotational gas temperature by adding a small amount of H2 in dry air to better detect OH (A-X) spectra. The rotational temperatures in humid air plasma column (50% of humidity) are larger than those of dry air plasma column by practically 30% near the nozzle of resonant cavity on the axis of the plasma column. This is partly due to attachment heating processes initiated by water vapor. A maximum of the measured absolute nitrogen density is also observed near the nozzle which is also larger for humid air plasma column. The obtained dissociation degrees of molecular nitrogen in both dry and humid air plasma along the air plasma column are lower than the cases where only thermodynamic equilibrium is assumed. This is characteristic of the absence of chemical and energetic equilibria not yet reached in the air plasma column dominated by recombination processes.

Two-Dimensional Talbot Effect with Atomic Density Gratings

We report the experimental observation of two-dimensional Talbot effect when a resonance plane wave interacts with a two-dimensional atomic density grating generated by standing wave manipulation of ultracold Bose gases. Clear self-images of the grating and sub-images with reversed phase or fractal patterns are observed. By calculating the autocorrelation functions of the images, the behavior of periodic Talbot images is studied. The Talbot effect with two-dimensional atomic density grating expands the applications of the Talbot effect in a wide variety of research fields.

Geometric properties of the first singlet S-wave excited state of two-electron atoms near the critical nuclear charge

The geometric structure parameters and radial density distribution of 1s2s1S excited state of the two-electron atomic system near the critical nuclear charge Z_(c)were calculated in detail under tripled Hylleraas basis set.Contrary to the localized behavior observed in the ground and the doubly excited 2p^(23)Pe states,for this state our results identify that while the behavior of the inner electron increasingly resembles that of a hydrogen-like atomic system,the outer electron in the excited state exhibits diffused hydrogen-like character and becomes perpendicular to the inner electron as nuclear charge Z approaches Z_(c).This study provides insights into the electronic structure and stability of the two-electron system in the vicinity of the critical nuclear charge.

Tailoring local structures of atomically dispersed copper sites for highly selective CO_(2) electroreduction

Atomically‐dispersed copper sites coordinated with nitrogen‐doped carbon(Cu–N–C)can provide novel possibilities to enable highly selective and active electrochemical CO_(2) reduction reactions.However,the construction of optimal local electronic structures for nitrogen‐coordinated Cu sites(Cu–N_(4))on carbon remains challenging.Here,we synthesized the Cu–N–C catalysts with atomically‐dispersed edge‐hosted Cu–N_(4) sites(Cu–N_(4)C_(8))located in a micropore between two graphitic sheets via a facile method to control the concentration of metal precursor.Edge‐hosted Cu–N_(4)C_(8) catalysts outperformed the previously reported M–N–C catalysts for CO_(2)‐to‐CO conversion,achieving a maximum CO Faradaic efficiency(FECO)of 96%,a CO current density of–8.97 mA cm^(–2) at–0.8 V versus reversible hydrogen electrode(RHE),and over FECO of 90%from–0.6 to–1.0 V versus RHE.Computational studies revealed that the micropore of the graphitic layer in edge‐hosted Cu–N_(4)C_(8) sites causes the d‐orbital energy level of the Cu atom to shift upward,which in return decreases the occupancy of antibonding states in the*COOH binding.This research suggests new insights into tailoring the locally coordinated structure of the electrocatalyst at the atomic scale to achieve highly selective electrocatalytic reactions.

Accelerating the design of catalysts for CO_(2)electroreduction to HCOOH:A data-driven DFT-ML screening of dual atom catalysts

Dual-atom catalysts(DACs)have emerged as potential catalysts for effective electroreduction of CO_(2)due to their high atom utilization efficiency and multiple active sites.However,the screening of DACs remains a challenge due to the large number of possible combinations,making exhaustive experimental or computational screening a daunting task.In this study,a density functional theory(DFT)-based machine learning(ML)-accelerated(DFT-ML)hybrid approach was developed to test a set of 406 dual transition metal catalysts on N-doped graphene(NG)for the electroreduction of CO_(2)to HCOOH.The results showed that the ML algorithms can successfully capture the relationship between the descriptors of the DACs(inputs)and the limiting potential for HCOOH generation(output).Of the four ML algorithms studied in this work,the feedforward neural network model achieved the highest prediction accuracy(the highest correlation coefficient(R^(2))of 0.960 and the lowest root mean square error(RMSE)of 0.319 eV on the test set)and the predicted results were verified by DFT calculations with an average absolute error of 0.14 eV.The DFT-ML approach identified Co-Co-NG and Ir-Fe-NG as the most active and stable electrocatalysts for the electrochemical reduction of CO_(2)to HCOOH.The DFT-ML hybrid approach exhibits exceptional prediction accuracy while enabling a significant reduction in screening time by an impressive 64%compared to conventional DFT-only calculations.These results demonstrate the immense potential of using ML methods to accelerate the screening and rational design of efficient catalysts for various energy and environmental applications.

Single-atom catalysts based on polarization switching of ferroelectric In_(2)Se_(3) for N_(2) reduction

The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In_(2)Se_(3).During the polariza-tion switching process,the difference in surface electrostatic potential leads to a redistribution of electronic states.This affects the interaction strength between the adsorbed small molecules and the catalyst substrate,thereby altering the reaction barrier.In addition,the surface states must be considered to prevent the adsorption of other small molecules(such as *O,*OH,and *H).Further-more,the V@↓-In_(2)Se_(3) possesses excellent catalytic properties,high electrochemical and thermody-namic stability,which facilitates the catalytic process.Machine learning also helps us further ex-plore the underlying mechanisms.The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.

DFT Study of Alkali Metal Atom Adsorption on Defect-Free MgO（001）Surface

The adsorption of isolated alkali metal atoms （Li, Na, K, Rb, and Cs） on defect-free sur- face of MgO（001） has been systemically investigated with density functional theory using a pseudopotential plane-wave approach. The adsorption energy calculated is about -0.72 eV for the lithium on top of the surface O site and about one third of this value for the other alkali metals. The relatively strong interaction of Li with the surface O can be explained by a more covalent bonding involved, evidenced by results of both the projected density of states and the charge density difference. The bonding mechanism is discussed in detail for all alkali metals.

Experimental and Theoretical Study of Hydrogen Atom Abstraction from C2H6 and C4H10 by Zirconium Oxide Clusters Anions

The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H- and Zr3O7H- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr2O5- with C2H6, which supports that the observed Zr2O5H- and Zr3O7H- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.

Studies on the Quantitative Structure-activity Relationship of Toxicity of Chlorophenol Serial Compounds in the ab initio Methods and Substitutive Position of Chlorine Atom (N_(PCS))

20 Quantum chemical parameters of chlorophenol compounds were fully optimized by using B3LYP method on both 6-31G^＊ and 6-311G^＊ basis sets. These structural parameters are taken as theoretical descriptors, and the experimental data of 20 compounds＇ aquatic photogen toxicity（-lgEC50） are used to perform stepwise regression in order to obtain two predicted -lgEC50 correlation models whose correlation coefficients R^2 are respectively 0.9186 and 0.9567. In addition, parameters of chlorine atom＇s substitutive positions and their correlations （NPCs） are taken as descriptors to obtain another predicted -lgEC50 model with the correlation coefficient R2 of 0.9444. Correlation degree of each independent variable in the three models is verified by using variance inflation factors （VIF） and t value. In the cross-validation method, cross-validation coefficients q^2 of 3 models are respectively 0.8748, 0.9119 and 0.8993, which indicates that the relativity and prediction ability of this model are superior to those of the model obtained by topological and BLYP methods.

Benchmark Calculations on the Atomization Enthalpy,Geometry and Vibrational Frequencies of UF_6 with Relativistic DFT Methods

Benchmark calculations on the molar atomization enthalpy, geometry, and vibrational frequencies of uranium hexafluoride （UF6） have been performed by using relativistic density functional theory （DFT） with various levels of relativistic effects, different types of basis sets, and exchange-correlation functionals. Scalar relativistic effects are shown to be critical for the structural properties. The spin-orbit coupling effects are important for the calculated energies, but are much less important for other calculated ground-state properties of closed-shell UF6. We conclude through systematic investigations that ZORA- and RECP-based relativistic DPT methods are both appropriate for incorporating relativistic effects. Comparisons of different types of basis sets （Slater, Gaussian, and plane-wave types） and various levels of theoretical approximation of the exchange-correlation functionals were also made.

Oxygen Atom Exchange Mechanism in Reaction of OH Radical with AsO

Oxygen atom exchange reaction mechanism in the reaction of OH radicals with AsO was investigated by means of the density functional theory (DFT) with 6 311++G( 3df,3pd ) and 6 311++G( d,p ) basis sets. The calculated results suggest that the reaction between OH and AsO should make the oxygen atoms exchange rapidly because the barrier to isomerization is significantly less than the HO-AsO bond dissociation energy.