Applying Density Functional Theory Calculations Research Articles

A density functional study on the formaldehyde recognition by Al-doped ZnO nanosheet

Experimental works have shown that doping ZnO nanosheets by the Al atom meaningfully increases their sensitivity toward HCHO gas. Here, we applied density functional theory calculations to study the Al-doping effect on the sensitivity of a ZnO nanosheet to HCHO gas, explaining the experimental results. We found that the pristine ZnO nanosheet weakly interacts with the HCHO with adsorption energy (Ead) of −9.3 kcal/mol, and the sensing response (S) value of 2.2 at 623 K. After the Al-doping process, the Ead and S values increase to −40.7 kcal/mol and 83.9, respectively, indicating an excellent agreement with the experimental results. We showed a relation between the HOMO-LUMO gap and the S value, confirming with the experimental results. Also, the proposed Al-doped ZnO nanosheet shows a good selectivity to HCHO gas at the presence of H2, NH3, C2H5OH, CO, and CH4 gases. A short recovery time of 18 s is predicted for Al–ZnO-based sensor which is comparable with the experimental value of 26 s. Finally, we conclude that the Al-doping makes the ZnO nanosheet a promising HCHO gas sensor with a high sensitivity, an excellent selectivity, and short recovery time.

Effect of Water Molecule on Photo-Assisted Nitrous Oxide Decomposition over Oxotitanium Porphyrin: A Theoretical Study

Water vapor has generally been recognized as an inhibitor of catalysts in nitrous oxide (N2O) decomposition because it limits the lifetime of catalytic reactors. Oxygen produced in reactions also deactivates the catalytic performance of bulk surface catalysts. Herein, we propose a potential catalyst that is tolerant of water and oxygen in the process of N2O decomposition. By applying density functional theory calculations, we investigated the reaction mechanism of N2O decomposition into N2 and O2 catalyzed by oxotitanium(IV) porphyrin (TiO-por) with interfacially bonded water. The activation energies of reaction Path A and B are compared under thermal and photo-assisted conditions. The obtained calculation results show that the photo-assisted reaction in Path B is highly exothermic and proceeds smoothly with the low activation barrier of 27.57 kcal/mol at the rate determining step. The produced O2 is easily desorbed from the surface of the catalyst, requiring only 4.96 kcal/mol, indicating the suppression of catalyst deactivation. Therefore, TiO-por is theoretically proved to have the potential to be a desirable catalyst for N2O decomposition with photo-irradiation because of its low activation barrier, water resistance, and ease of regeneration.

A computational study on the potential application of zigzag carbon nanotubes in Mg-ion batteries

Although Li-ion batteries are extensively applied for different purposes, they suffer from safety problems, high cost, and short lifetime. Because of low cost, wide availability, and nontoxicity of magnesium, Mg-ion batteries (MIB) might be a good alternative to Li-ion batteries. Here, applying density functional theory calculations, we examined the potential application of zigzag (4,0), (5,0), (6,0), (7,0), and (8,0) carbon nanotubes in the anode of MIBs. We found that by increasing the tube diameter, the Mg2+ adsorption energies are very slightly changed but the Mg adsorption sharply decreased indicating that the adsorption of Mg atom much more depends on the tube diameter and its adsorption energy is the key parameter for generating a cell voltage. We showed that by increasing the curvature of the CNT, the charge transfer is sharply increased upon Mg atom so that in the highest curvature, the interaction becomes ionic in nature with a Jahn-Teller distortion in the CNT structure. However, by increasing the CNT diameter, the cell voltage of MIB increased, from 4.0 V in the (4,0) to 5.3 V in the (8,0) CNT.

Density Functional Theory (DFT)-Based Bonding Analysis Correlates Ligand Field Strength with 99Ru Mössbauer Parameters of Ruthenium-Nitrosyl Complexes.

We applied density functional theory calculations to ruthenium-nitrosyl complexes, which are known to exist in high-level radioactive waste generating during reprocessing of spent nuclear fuel, to give a theoretical correlation between 99Ru Mössbauer spectroscopic parameters and ligand field strength for the first time. The structures of the series of complexes, [Ru(NO)L5] (L = Br-, Cl-, NH3, CN-), were modeled based on the corresponding single-crystal X-ray coordinates. The comparisons of the geometries and total energies between the different spin states suggested that the singlet spin state of [Ru(II)(NO+)L5] complexes were the most stable. This result was supported by the benchmark calculations of the 99Ru Mössbauer isomer shift (δ) and quadrupole splitting (ΔEQ) values. The calculated results of both the δ and ΔEQ values reproduced the experimental results by reported previously and increased in the order of L = Br-, Cl-, NH3, CN-. Finally, we estimated the ligand field strength (Δo) based on molecular orbitals, assuming C4v symmetry and showed the increase of Δo values in that order, being consistent with well-known spectrochemical series of ligands. The increase attributes to the strengthening of the abilities of σ-donor and π-acceptor of the L-ligands to the Ru atom, resulting in the increase of the δ values. Furthermore, the increase of the σ-type donation into Ru dx2-y2 orbital and the π-type back-donation from Ru dxz, dyz orbitals in that order caused the decrease of the electron density along the Ru-NO axis, resulting in the increase of the ΔEQ values. This study is expected to contribute to the ligand design for the ruthenium-nitrosyl complexes, leading to the drug design for NO carrier and the decontamination of radioactive ruthenium from the ecological system, as well as the recovery of platinum-group metals from high-level radioactive waste.

Computational Study of Methane Activation on γ-Al2O3.

The C–H activation of methane remains a longstanding challenge in the chemical industry. Metal oxides are attractive catalysts for the C–H activation of methane due to their surface Lewis acid–base properties. In this work, we applied density functional theory calculations to investigate the C–H activation mechanism of methane on various sites of low-index facets of γ-Al2O3. The feasibility of C–H activation on different metal–oxygen (acid–base) site pairs was assessed through two potential mechanisms, namely, the radical and polar. The effect of surface hydroxylation on C–H activation was also investigated to examine the activity of γ-Al2O3 under realistic catalytic surface conditions (hydration). On the basis of our calculations, it was demonstrated that the C–H activation barriers for polar pathways are significantly lower than those of the radical pathways on γ-Al2O3. We showed that the electronic structure (s- and p-band center) for unoccupied and occupied bands can be used to probe site-dependent Lewis acidity and basicity and the associated catalytic behavior. We identified the dissociated H2 binding and final state energy as C–H activation energy descriptors for the preferred polar pathway. Finally, we developed structure–activity relationships for the C–H activation of methane on γ-Al2O3 that account for surface Lewis acid–base properties and can be utilized to accelerate the discovery of catalysts for methane (and shale gas) upgrade.

Fully spin-polarized current in gated bilayer silicene

By applying density functional theory calculations, we predict that the groundstate of bilayer silicene at certain interlayer distances can be antiferromagnetic. At small electron or hole doping, it becomes half metallic under applied out-of-plane electric field, which can be used to produce fully spin-polarized field-effect-driven current even in the absence of external magnetic field, ferromagnetic substrates, doped magnetic ions, or spin-orbital coupling. Our finding points out a new route to overcome the major challenge of spintronics.

Thermodynamic and Kinetic Limitations for Peroxide and Superoxide Formation in Na-O2 Batteries.

The Na-O2 system holds great potential as a low-cost, high-energy-density battery, but under normal operating conditions, the discharge is limited to sodium superoxide (NaO2), whereas the high-capacity peroxide state (Na2O2) remains elusive. Here, we apply density functional theory calculations with an improved error-correction scheme to determine equilibrium potentials and free energies as a function of temperature for the different phases of NaO2 and Na2O2, identifying NaO2 as the thermodynamically preferred discharge product up to ∼120 K, after which Na2O2 is thermodynamically preferred. We also investigate the reaction mechanisms and resulting electrochemical overpotentials on stepped surfaces of the NaO2 and Na2O2 systems, showing low overpotentials for NaO2 formation (ηdis = 0.14 V) and depletion (ηcha = 0.19 V), whereas the overpotentials for Na2O2 formation (ηdis = 0.69 V) and depletion (ηcha = 0.68 V) are found to be prohibitively high. These findings are in good agreement with experimental data on the thermodynamic properties of the Na xO2 species and provide a kinetic explanation for why NaO2 is the main discharge product in Na-O2 batteries under normal operating conditions.

Reactivity of CO on Ni4 cluster- effect of spin multiplicity and H doping-A DFT investigation

We investigated the reactivity of carbon monoxide on tetrahedral Ni4 clusters at different spin multiplicity applying density functional theory calculations considering pure and hybrid functional. The stability of the clusters increases with the increasing spin multiplicity and doping hydrogen in Ni4 cluster. The adsorption or binding energy of CO on Ni4 cluster is thermodynamically feasible process at normal condition whereas dissociation is not feasible. Ab initio molecular orbital analysis shows the orbital overlaps are observed at bridging site, three fold sites, and tetra coordinated centre and formation of δ-bond in the cluster. In NBO analysis, CO binds strongly to the Ni4 cluster not only by two NiC bond (spd hybrid), but also donor-acceptor delocalization interactions, for example, σ type BD(CO) → BD*(NiC) and BD(NiC) → BD*(NiC/CO), two π-type BD(CO) → LP*(Ni) and several diffuse RY*(C) ← LP(Ni) and π*(CO) ← LP(Ni) interactions. Singlet Ni4 cluster shows highest activation energy barrier, 3 eV. H-doped Ni4 cluster decreases dissociation barrier and favors CH bond formation.

Influence of the N-3 alkyl chain length on improving inhibition properties of imidazolium-based ionic liquids on copper corrosion

1-butyl-3-ethylimidazolium bromide ionic liquid, [beim]Br, was studied experimentally and theoretically as a potential inhibitor of copper corrosion in acidic media (pH = 3) by dc polarization, quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and density functional theory (DFT). This ionic liquid is selected to study an effect of the alkyl chain length at the position N-3, since so far only ionic liquids with different alkyl substituents at the position N-1 are investigated. Improved inhibitory properties of the investigated ionic liquid against corrosion of copper in acidic solution at the given conditions are confirmed comparing to corresponding 1-butyl-3-methylimidazolium bromide ionic liquid. It is found that [beim]Br acts as a cathodic corrosion inhibitor, whereby its effectiveness depends on the applied concentration. The inhibitory effect of the studied ionic liquid (IL) was achieved through quick and spontaneous adsorption on the copper surface following the Langmuir's adsorption isotherm. Results obtained by SEM showed that copper protection is achieved through the less damaged copper surface in the presence of inhibitor. Applying DFT calculations, it is found that interactions with the metal surface occur by donating electron from the Br− anion to the copper. Based on the obtained Fukui functions influence of the inductive effect of ethyl/methyl group on the inhibitory activity is also discussed.

Polarizability of the Si60H60 Derivatives Containing Epoxide Moieties (Si60H60−2nOn with n up to 30): A DFT Study

We have applied density functional theory calculations to study polarizability of the Si60H60 derivatives with epoxide moieties (Si60H60−2nOn with n up to 30). The results show that mean polarizability, α, of oxygen-containing silicon fullerene derivatives is higher than that of Si60H60. The mean polarizabilities of the isomers slightly depend on the positional relationship of the epoxide moieties, and are determined mainly by the number of epoxide moieties. Mean polarizabilities of Si60H60−2nOn linearly increase with n, and are characterized by the depression of polarizability. The formula describing the mean polarizability as a function of the number of epoxide groups has been obtained, which may be important for the design of silicon-containing nanostructures with regulated polar parameters.

Catalytic Thermodynamics of Nanocluster Adsorbates from Informational Statistical Mechanics

This letter presents a new approach for studying the catalytic thermodynamics of cuboctahedral nanoclusters, using informational statistical mechanics. The Morse potential determines bond energies between cluster atoms in a coordination type calculation. Applied density functional theory calculations demonstrate adatom effects on the thermodynamic quantities, which are derived from a Hamiltonian. Calculations of the entropy, free energy, and total energy show linear behavior, as the coverage of oxygen on platinum, and hydrogen on palladium, increases from bridge sites on the surface. The data exhibits size effects for the measured thermodynamic properties with cluster diameters between 2 and 5 nm. Entropy and enthalpy calculations of Pt–O2 compare well with previous theoretical data for Pt(111)–O2, and trends for Pd–H are similar to experimental measurements on Pd–H2 nanoclusters. These techniques are applicable to a wide variety of cluster–adsorbate interactions, encouraging further research.

Correlation between Am(III)/Eu(III) selectivity and covalency in metal–chalcogen bonds using density functional calculations

We applied density functional theory calculations to Am(III) and Eu(III) complexes with chalcogen-donor ligands of the formula N(EPMe2) 2 − (E = O, S, Se, Te). We calculated the equilibrium structures and relative stabilities of the complexes in the complexation reaction. The results indicated that the tendency of the relative stability is O ≪ S ~ Se ~ Te, which is consistent with the trend of soft acid classification. Molecular orbital overlap population analysis suggested that this tendency can be correlated with the bonding type in the covalent interaction between the f-orbitals of the metal atom and the chalcogen-donor atoms.

Carboxylic Acid Group-Induced Oxygen Vacancy Migration on an Anatase (101) Surface.

Dye-sensitized solar cells (DSSCs) have aroused intensive interest for the replacement of conventional crystalline silicon solar cells. Through carboxylic acid groups, the dyes attach to the TiO2 anatase (101) surface, on which the subsurface oxygen vacancies (Vosubs) are predominant. The performance of DSSCs can be affected by the presence and positions of oxygen vacancies (Vos). By applying density functional theory calculations, we found that the adsorption of a carboxylic acid group-decorated dye molecule reverses the relative stability between the surface oxygen vacancy (Vosurf) and Vosub on the anatase (101) surface, which facilitates the migration of the Vo from the subsurface to the surface by overcoming an energy barrier of less than 0.16 eV, which is significantly lower than the 1.01 eV energy barrier on the clean surface. Further, ab initio molecular dynamics simulations indicate that the Vosub can easily migrate to the surface at room temperature. This dynamic interplay between the Vo of the anatase (101) surface and the carboxylic acid group would be important for future studies concerning the stability and photovoltaic efficiency of the solar cells.

Hydrogen-abstraction reactions of fully hydrogenated silicon fullerene cages with the amino radical: a density functional study

We applied density functional theory calculations to study reactions NH2 •+ SinHn fullerenes (n = 4, 6, 8, 10, 20, 24, 30, 36, and 50). The reactions between SinHn fullerenes and NH2 • radical are obtained to be exothermic, proceeding through a hydrogen-bonded prereactive complex. The resemblance between the structures of the reactants and the transition states indicates that the transition states appear earlier for the considered exothermic reactions. The calculated ΔH0 298 and ΔETS are in good correlation with the spherical excesses φi, showing upward trend with increasing curvature on silicon sites. The reactions of Si20H20 and Si20F20 with NH2 • and NF2 • radicals were also investigated. The reaction between Si20H20 and NF2 • radical also proceeds through a hydrogen-bonded prereactive complex. However, this reaction is endothermic, and as compared with the reaction of NH2 •+ Si20H20, the prereactive complex has stronger hydrogen bonding which leads to higher activation barrier. The reaction of Si20F20 and NF2 • radical as well as NH2 • radical is obtained to be endothermic, having significantly higher barriers via “late” transition states, in comparison to the reaction of NH2 •+ Si20H20.

Hydrogen-abstraction reactions of fully hydrogenated fullerene cages with the amino radical: a density functional study

ABSTRACTWe have applied density functional theory calculations to study the reactions of NH2 + CnHn (n = 20, 40, 50, 60, 70 and 80). Due to the hard curvature in C20 cage, the NH2• + C20H20 → NH3 + C20H19• reaction is nearly thermoneutral with a high potential barrier height. For the CnHn fulleranes with n > 20 the transition states appear earlier on the reaction paths, as can be anticipated for exothermic reactions. Using the spherical excess parameter, we distinguished different curvatures on the surfaces of fullerane cages. The reaction enthalpies ΔH°298 and potential barrier heights ΔETS of the considered reactions indicate good correlation with the values of ϕi parameter, showing an upward trend with the curvature increasing at carbon sites. We have also investigated the H-abstraction of the chemical derivatives of the C20H20 cage (C20H19–CH3, C20H19–CH2CH3 and C20H19–CH2CH2CH3) in comparison to the corresponding isolated alkanes (CH4, C2H6 and C3H8). Overall, it could be inferred that the H-abstraction from the primary and secondary C–H bonds of isolated alkanes could occur more easily than fullarane derivatives.

Interaction and Quantum Capacitance of Nitrogen/Sulfur Co-Doped Graphene: A Theoretical Calculation

The interaction between different configurations of nitrogen and sulfur, as well as the influence on the quantum capacitance of N/S co-doped graphene. was investigated by applying density functional theory calculations. It was found that the sulfur atom tends to dislocate from the graphene plane in the presence of a pyrrolic-N atom. However, in the presence of pyridinic-N, the sulfur atom maintains its sp2 hybridization in both 6- and 5-membered rings. Moreover, at low concentration, sulfur doping produces a new state close to the Fermi level, which enhances the maximum quantum capacitance of the co-doped graphene up to 50%. Nevertheless, there is no further improvement when another nitrogen or sulfur atom was embedded into the co-doped graphene.

Crystallographic structure and energetics of the Rh(1 0 0)-(3 × 1)-2O phase

In this study we investigate the crystallographic structure of the Rh(1 0 0)-()-2O phase by quantitative low energy electron diffraction (LEED) and scanning tunnelling microscopy as well as the energetics of the system applying density functional theory calculations (DFT). The () structure forms upon exposing the clean Rh(1 0 0) surface to 1200 L of oxygen at 520 K. A full-dynamical LEED intensity analysis (Pendry R-factor ) reveals an oxygen-induced shifted row-reconstruction of the rhodium top layer where every third Rh-row is displaced by half a surface lattice parameter along the [0 1 1]-direction. There are two oxygen atoms within the unit cell which assume threefold coordinated sites on both sides of the shifted Rh-row with one bond to the shifted and two bonds to the unshifted rows. DFT calculations yield a total energy gain of 0.27 eV per oxygen atom compared to adsorption on the unreconstructed surface. This by far overcompensates the energetic penalty of 0.10 eV per oxygen atom for shifting the Rh-row and thus drives the substrate reconstruction. A coadsorption of oxygen at remaining regular sites of the substrate is not observed in experiment and is found to be energetically unfavorable.

Computational Design Principles of Two-Center First-Row Transition Metal Oxide Oxygen Evolution Catalysts

Computational screens for oxygen evolution reaction (OER) catalysts based on Sabatier analysis have seen great success in recent years; however, the concept of using chemical descriptors to form a reaction coordinate has not been put under scrutiny for complex systems. In this paper, we examine critically the use of chemical descriptors as a method for conducting catalytic screens. Applying density functional theory calculations to a two-center metal oxide model system, we show that the Sabatier analysis is quite successful for predicting activities and capturing the chemical periodic trends expected for the first-row transition metal series, independent of the proposed mechanism. We then extend this analysis to heterodimer metallic systems—metal oxide catalysts with two different catalytically active metal centers—and find signs that the Sabatier analysis may not hold for these more complex systems. By performing a principal component analysis on the computed redox potentials, we show (1) that a single c...

Theoretical investigation of interactions between palladium and fullerene in polymer

Applying density functional theory (DFT) calculations, we predict the structural and electronic properties of different types of palladium–fullerene polymers.

Electronic structures and quantum capacitance of monolayer and multilayer graphenes influenced by Al, B, N and P doping, and monovacancy: Theoretical study

Graphene has been extensively explored as an electrode material in supercapacitors because of its large surface area and high electronic conductivity. By designing diverse morphologies and doping graphene with certain elements, the properties of graphene can be efficiently modified. We present the influence of Al, B, N and P doping, monovacancy and multilayer graphene structures on stability, electronic structures and quantum capacitance, by applying density functional theory calculations. The electrode quantum capacitances are substantially modified due to doping, the presence of monovacancy, and interaction between layers occurred in multilayer structures. Our calculations suggest that the monolayer graphene with monovacancy, the monolayer and multilayer graphene structures with nitrogen doped around the monovacancy, and multilayer graphene structure with aluminum doped could provide substantial change of quantum capacitance. However, the structure stability could be challenging. The interaction between layers could lower quantum capacitances compared to those of the monolayer structures with the same dopant elements. Moreover, the association of monovacancy and nitrogen doping of a single layer structure could lead to as high quantum capacitance as ∼80 μF/cm2. This work suggests the possibility to enhance quantum capacitance of the graphene-based electrodes using the combination effect of doping, vacancy defect and stacking layers.