Effects of zinc on χ-Fe_(5)C_(2) for carbon dioxide hydrogenation to olefins:Insights from experimental and density function theory calculations

Production of light olefins from CO_(2), the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO_(2) emission on environment and to supply the value-added products from nonpetroleum resource. However, development of robust catalyst with controllable selectivity and stability remains a challenge. Herein, we report that Zn-promoted Fe catalyst can boost the stable and selective production of light olefins from CO_(2). Specifically, the Zn-promoted Fe exhibits a highly stable activity and olefin selectivity over 200 h time-on-stream compared to the unpromoted Fe catalyst, primarily owing to the preservation of active χ-Fe_(5)C_(2) phase. Structural characterizations of the spent catalysts suggest that Zn substantially regulates the content of iron carbide on the surface and suppresses the reoxidation of bulk iron carbide during the reaction. DFT calculations confirm that adsorption of surface carbon atoms and graphene-like carbonaceous species are not thermochemically favored on Zn-promoted Fe catalyst. Carbon deposition by CAC coupling reactions of two surface carbon atoms and dehydrogenation of CH intermediate are also inhibited. Furthermore, the effects of Zn on antioxidation of iron carbide were also investigated. Zn favored the hydrogenation of surface adsorbed oxygen atoms to H_(2)O and the desorption of H_(2)O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.

Electronic structure and optical properties of Nb-doped Sr_2TiO_4 by density function theory calculation

This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory （DFT）.The calculated results reveal that due to the electron doping,the Fermi level shifts into conduction bands（CBs） for Sr2NbxTi1-xO4 with x=0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes,and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region.The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.

Investigation of the structural, electronic and mechanical properties of CaO–SiO_(2) compound particles in steel based on density functional theory

CaO–SiO_(2)compounds compromise one of the most common series of oxide particles in liquid steels, which could significantly affect the service performance of the steels as crack initiation sites. However, the structural, electronic, and mechanical properties of the compounds in CaO–SiO_(2)system are still not fully clarified due to the difficulties in the experiments. In this study, a thorough investigation of these properties of CaO–SiO_(2)compound particles in steels was conducted based on first-principles density functional theory. Corresponding phases were determined by thermodynamic calculation, including gamma dicalcium silicate(γ-C2S), alpha-prime(L) dicalcium silicate(αL′-C2S), alpha-prime(H) dicalcium silicate(αH′-C2S), alpha dicalcium silicate(α-C2S), rankinite(C3S2), hatrurite(C3S), wollastonite(CS), and pseudowollastonite(Ps-CS). The results showed that the calculated crystal structures of the eight phases agree well with the experimental results. All the eight phases are stable according to the calculated formation energies, and γ-C2S is the most stable. O atom contributes the most to the reactivity of these phases. The Young’s modulus of the eight phases is in the range of 100.63–132.04 GPa. Poisson’s ratio is in the range of0.249–0.281. This study provided further understanding concerning the CaO–SiO_(2)compound particles in steels and fulfilled the corresponding property database, paving the way for inclusion engineering and design in terms of fracture-resistant steels.

Insights into SO_2 and H_2O co-adsorption on Cu(100) surface with calculations of density functional theory

The co-adsorption behaviors of SO2 and H2 O on face-centered cubic Cu（100） ideal surface were studied using the GGA-r PBE method of density functional theory（DFT） with slab models. The optimized structures of single H2 O and SO2 on Cu（100） surface were calculated at the coverage of 0.25 ML（molecular layer） and 0.5 ML. The results show that there was no obvious chemical adsorption of them on Cu（100） surface. The adsorbed structures, adsorption energy and electronic properties including difference charge density, valence charge density, Bader charge analysis and partial density of states（PDOS） of co-adsorbed structures of H2 O and SO2 were investigated to illustrate the interaction between adsorbates and surface. H2 O and SO2 can adsorb on surface of Cu atoms chemically via molecule form at the coverage of 0.25 ML, while H2 O dissociated into OH adsorbed on surface and H bonded with SO2 which keeps away from surface at the coverage of 0.5 ML.

Density functional theory study of NO_2 -sensing mechanisms of pure and Ti-doped WO_3 (002) surfaces

Density functional theory （DFT） calculations are employed to explore the NO2-sensing mechanisms of pure and Ti-doped WO3 （002） surfaces. When Ti is doped into the WO3 surface, two substitution models are considered： substitution of Ti for W6c and substitution of Ti for Wsc. The results reveal that substitution of Ti for 5-fold W forms a stable doping structure, and doping induces some new electronic states in the band gap, which may lead to changes in the surface properties. Four top adsorption models of NO2 on pure and Ti-doped WO3 （002） surfaces are investigated： adsorptions on 5-fold W （Ti）, on 6-fold W, on bridging oxygen, and on plane oxygen. The most stable and likely NO2 adsorption structures are both N-end oriented to the surface bridge oxygen Olc site. By comparing the adsorption energy and the electronic population, it is found that Ti doping can enhance the adsorption of NO2, which theoretically proves the experimental observation that Ti doping can greatly increase the WO3 gas sensor sensitivity to NO2 gas.

Density functional theory study of CO catalytic oxidation on Co_2B_2/TiO_2(110) surface

Titanium dioxide with CoB amorphous alloys nanoparticles deposited on the surface is known to exhibit higher catalytic activity than the CoB amorphous.A study of the structure of such system is necessary to understand this effect.A quantum chemical study of Co2B2 on the TiO2（110） surface was studied using periodic slab model within the framework of density functional theory（DFT）.The results of geometry optimization indicated that the most stable model of adsorption was Co2B2 cluster adsorbed on the hollow site of TiO2 .The adsorption energy calculated for Co2B2 on the hollow site was 439.3 kJ/mol.The adsorption of CO and O2 was further studied and the results indicated that CO and O2 are preferred to adsorb on the Co2 site.Co-adsorption of CO and O2 shows that Co2B2 /TiO2 is a good catalyst for the oxidation of CO to carbon dioxide in the presence of oxygen.

Density functional theory study of Mg_nNi_2(n=1-6) clusters

The geometries of MgnNi2（n = 1 6） clusters are studied by using the hybrid density functional theory （B3LYP） with LANL2DZ basis sets. For the ground-state structures of MgnNi2 clusters, the stabilities and the electronic properties are investigated. The results show that the groundstate structures and symmetries of Mg clusters change greatly due to the Ni atoms. The average binding energies have a growing tendency while the energy gaps have a declining tendency. In addition, the ionization energies exhibit an odd-even oscillation feature. We also conclude that n = 3, 5 are the magic numbers of the MgnNi2 clusters. The Mg3Ni2 and Mg5Ni2 clusters are more stable than neighbouring clusters, and the MgaNi2 cluster exhibits a higher chemical activity.

Effects of hydroxyl group on H_2 dissociation on graphene:A density functional theory study

Graphene-based materials are promising for hydrogen production and storage. In this work, using density functional theory calculations, we explored how a hydroxyl group influences H2 dissociation on graphene. Presence of the hydroxyl group makes the binding of H atom with graphene stronger, as the binding energy of H atom with the hydroxyl-modified graphene is higher than that with the pristine graphene. The para-site is the most favorable site for H2 dissociation on both the pristine and hydroxyl-modified graphene. The energy barrier of H2 dissociation at para-site on the pristine graphene is 3.10 eV whereas that on the hydroxyl-modified graphene is 2.46 eV, indicating a more facile H2 dissociation on the hydroxyl-modified graphene.

Comparative Studies of 1,4-Bis[2-(4-Pyridyl)ethenyl]-benzene Using Density Functional Theory

The optimized molecular structure and harmonic vibrational frequencies of a 1,4-bis [ 2-（4-pyridyl）ethenyl]- benzene（BPENB） molecule were calculated via five popular density functional theory（DFI＇） methods. On the basis of the comparison between calculated and experimental results, it is concluded that the B3PW91 and B3LYP methods are superior to the others in optimizing structures, and the BPW91 method reproduces the observed fundamental fre-quencies most satisfactorily.

Adsorption of H2O, OH, and O on CUCl（111） Surface： A Density Functional Theory Study

The adsorption of H2O molecule and its dissociation products, O and OH, on CuCl（111） surface was studied with periodic slab model by PW91 approach of GGA within the framework of density functional theory. The results of geometry optimization indicate that the top site is stable energetically for H2O adsorbed over the CuCl（111） surface. The threefold hollow site is found to be the most stable adsorption site for OH and O, and the calculated adsorption energies are 309.5 and 416.5 kJ/mol, respectively. Adsorption of H20 on oxygen-precovered CuCl（111） surface to form surface hydroxyl groups is predicted to be exothermic by 180.1 kJ/mol. The stretching vibrational frequencies, Mulliken population analysis and density of states analysis are employed to interpret the possible mechanism for the computed results.

Density functional theory study of Mg_2Ni_n(n= 1–8) clusters

The density functional theory B3PW91 with LANL2DZ basis sets has been used to study the possible geometries of Mg2Nin(n = 1–8) clusters. For the lowest energy structures of the clusters, stabilities, electronic properties, and natural bond orbital(NBO) are calculated and discussed. The results show that the doped Mg atoms reduce the stabilities of pure Ni clusters. The Mg2Ni2, Mg2Ni4, and Mg2Ni6clusters are more stable than neighboring clusters. The system appears magic number characteristics. In addition, the hybridization phenomenon occurs, owing to the interaction of Mg and Ni. The result of charge transfer is that Ni atom is negative and the Mg atom is positive. We also conclude that the 3p and 4d orbitals of the Ni atom have an effect on the stabilities of the clusters.

Adsorption of NO on the M/c-ZrO_2(110)(M=Ru,Rh)Surface:A Density Functional Theory Study

The adsorption of NO on the M/c-ZrOu（110） （M = Ru, Rh） surface has been studied with periodic slab model by PWgl approach of GGA within the framework of density functional theory. The results of geometry optimization indicated that the hollow site is energetically stable for Ru and Rh atoms＇ adsorption on the c-ZrO2（110） surface with adsorption energies of 207.4 and 106.3 kJ/mol, respectively. When NO is adsorbed on the M/ZrO2（110） surface, the N-down adsorption is the most stable. We also studied the adsorption of double NO on the M/c-ZrOu（110） surface. Complete linear synchronous transit and quadratic synchronous transit approaches were used to search the transition state for dissociation reaction. NO has two possible dissociation passways： （1） 2NO → N2 （g） ＋ 20 （ads）, （2） 2NO→ N20 （g） ＋ O （ads）, and the former is easier than the latter based on the calculation results.

Density Functional Theory Study on the Adsorption of HCNH and CNH_2 on Cu(100) Surface

The HCNH and CNH2 adsorption on different coordination sites of Cu（100） was theoretically studied considering the cluster approach. The present calculations show that the bridge site is the most favorite for CNH2 perpendicularly adsorbed on the Cu（100） surface via the C atom. For HCNH absorbed on the Cu（100） surface, the parallel adsorption mode with the C and N atoms nearly directly above the adjacent top sites of Cu（100） surface is the most favored. Both CNH2 and HCNH are strongly bound to the Cu（100） surface with CNH2 which is lightly stable （2.51 kJ·mol^-1）, indicating that both species may be co-adsorbed on the Cu（100） surface.

New ternary superconducting compound LaRu2As2： Physical properties from density functional theory calculations

In this paper, we perform the density functional theory （DFT） -based calculations by the first-principles pseudopo- tential method to investigate the physical properties of the newly discovered superconductor LaRu2As2 for the first time. The optimized structural parameters are in good agreement with the experimental results. The calculated independent elas- tic constants ensure the mechanical stability of the compound. The calculated Cauchy pressure, Pugh＇s ratio as well as Poisson＇s ratio indicate that LaRu2As2 should behave as a ductile material. Due to low Debye temperature, LaRu2As2 may be used as a thermal barrier coating （TBC） material. The new compound should exhibit metallic nature as its valence bands overlap considerably with the conduction bands. LaRu2As2 is expected to be a soft material and easily machinable because of its low hardness value of 6.8 GPa. The multi-band nature is observed in the calculated Fermi surface. A highly anisotropic combination of ionic, covalent and metallic interactions is expected to be in accordance with charge density calculation.

Density functional theory study of the interaction of H_2 with pure and Ti-doped WO_3 (002) surfaces

Density functional theory （DFT） calculations are conducted to explore the interaction of H2 with pure and Tidoped WO3 （002） surfaces. Four top adsorption models of H2 on pure and Ti-doped WO3 （002） surfaces are investigated respectively, they are adsorption on bridging oxygen Olc, absorption on plane oxygen O2c, absorption on 5-fold W5c （Ti）, and absorption on 6-fold W6c. The most stable and H2 possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O2c site, while the favourable adsorption sites for H2 in a Ti-doped surface is not only an O2c site but also a W6c site. The adsorption energy, the Fermi energy level EF, and the electronic population are investigated and the H2-sensing mechanism of a pure-doped WO3 （002） surface is revealed theoretically： the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H2. It can be predicted that the method of Ti-doped into a WO3 thin film is an effective way to improve WO3 sensor sensitivity to H2 gas.

A density functional theory study on the adsorption of CO and O_2 on Cu-terminated Cu_2O(111) surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.

A Density Functional Theory (DFT) Investigation on the Structure and Spectroscopic Behavior of 2-Aminoterephthalic Acid and Its Sodium Salts

As a substitute for lithium ion batteries, Na chemistry for ion battery systems is promising materials for energy storage applications for the next generation. Herein, the structures, IR and UV-visible spectra of 2-aminoterephthalic acid (H2ATA), disodium 2-aminoterephthalate (Na2ATA), trisodium 2-aminotere-phthalate (Na3ATA) and tetrasodium 2-aminoterephthalate (Na4ATA) have been studied using density functional theory (DFT/B3LYP/6-311++G(d,p)). The theoretical geometric parameters and FTIR results showed very good agreement with the experimental results. Different conformers of Na2ATA, Na3ATA and Na4ATA showed that the binding energy per sodium in Na2ATA, Na3ATA and Na4ATA is -694.94, -543.44 and -407.46 kJ/mol, respectively. The Na3ATA and Na4ATA salts are higher in energy (151.46 and 287.48 kJ/mol, respectively) than Na2ATA, indicating the higher stability of the Na2ATA complex. The calculated binding energy, enthalpy and Gibbs free energy of Na2ATA, Na3ATA and Na4ATA revealed that the compounds are thermodynamically stable. Natural bond orbital (NBO) analysis of Na2ATA, Na3ATA and Na4ATA indicated that the major interaction occurs between the lone pair electrons of the oxygen atom and anti-bonding orbitals of carbon atoms of the two carboxylate ions. UV-visible spectrum of the free H2ATA and its sodium salts Na2ATA, Na3ATA and Na4ATA were performed using the time-dependent density functional theory (TD-DFT) method at the level of B3LYP/6-311++G(d,p). The frontier molecular orbital energetic parameters and global reactivity descriptors revealed that the Na4ATA and Na3ATA complexes exhibited a higher band gap (ΔEgap) and electronegativity (χeV) than Na2ATA.

Tuning electronic properties of the S2/graphene heterojunction by strains from density functional theory

Based on the density functional calculations, the structural and electronic properties of the WS2/graphene heterojunction under different strains are investigated. The calculated results show that unlike the free mono-layer WS2, the monolayer WS2 in the equilibrium WS2/graphene heterojunctionis characterized by indirect band gap due to the weak van der Waals interaction. The height of the schottky barrier for the WS2/graphene heterojunction is 0.13 eV, which is lower than the conventional metal/MoS2 contact. Moreover, the band properties and height of schottky barrier for WS2/graphene heterojunction can be tuned by strain. It is found that the height of the schottky barrier can be tuned to be near zero under an in-plane compressive strain, and the band gap of the WS2 in the heterojunction is turned into a direct band gap from the indirect band gap with the increasing schottky barrier height under an in-plane tensile strain. Our calculation results may provide a potential guidance for designing and fabricating the WS2-based field effect transistors.

Structural,Electrical,and Lithium Ion Dynamics of Li2MnO3 from Density Functional Theory

The layered Li2MnO3 is investigated by using the first-principles calculations within the GGA and GGA-t-U scheme, respectively. Within the GGA4-U approach, the calculated intercalation voltage （ranges from 4,5 V to 4.9 V） is found to be in good agreement with experiments. From the analysis of electronic structure, the pure phase Li2MnO3 is insulating, which is indicative of poor electronic-conduction properties. However, further studies of lithium ion diffusion in bulk Li2MnO3 show that unlike the two-dimensional diffusion pathways in rock salt structure layered cathode materials, lithium can diffuse in a three-dimensional pathway in Li2MnO3, with moderate lithium migration energy barrier ranges from 0.57 to 0.63 e V.

A Density Functional Theory Study of the Hydrates of 2NH_3:H_2SO_4 and Its Implications for the Formation of Atmosphere Particles

Density functional theory was used at the B3LYP/6-311＋＋G（d,p） level of theory to study the hydrates of 2NH3：H2SO4：nH2O for n = 0～4. Neutrals of the most stable clusters, when n = 0 and 1, spontaneously formed and were determined to be hydrogen-bonded molecular complexes of monomeric species. Double ions （clusters containing a NH4＋ cation and a HSO4- anion） or even ternary ions （clusters with two NH4＋ cations and one SO42- anion） spontaneously formed in the most stable clusters of 2NH3：H2SO4：nH2O （n = 2, 3, 4）. The energetics of binding and incremental association was also calculated. Double ions are not energetically favorable until 2NH3：H2SO4：2H2O because of the about equal free energies for forming the neutral （the most stable） and double ion （the second stable） isomers. The free energy of incremental association from free H2O and 2NH3：H2SO4：nH2O has a maximum at n = 2 at room temperature with ΔG ≈ –2 kcal/mol. The comparison of incremental association energies between 2NH3：H2SO4：nH2O, NH3：H2SO4：nH2O and H2SO4：nH2O clusters revealed that NH3 plays an important role in the atmospheric particle nucleation.