Adsorption properties of hydrazine on pristine and Si-doped Al12N12 nano-cage

The interaction of hydrazine (N₂H₄) molecule with pristine and Si-doped aluminum nitride (Al₁₂N₁₂) nano-cage was investigated using the density functional theory calculations. The adsorption energy of N₂H₄ on pristine Al₁₂N₁₂ in different configurations was about –1.67 and –1.64 eV with slight changes in its electronic structure. The results showed that the pristine nano-cage can be used as a chemical adsorbent for toxic hydrazine in nature. Compared with very low sensitivity between N₂H₄ and Al₁₂N₁₂ nano-cage, N₂H₄ molecule exhibits high sensitivity toward Si-doped Al₁₂N₁₂ nano-cage so that the energy gap of the Si-doped Al₁₂N₁₂ nano-cage is changed by about 31.86% and 37.61% for different configurations in the Si_Al model and by about 26.10% in the Si_N model after the adsorption process. On the other hand, in comparison with the Si_Al model, the adsorption energy of N₂H₄ on the Si_N model is less than that on the Si_Al model to hinder the recovery of the nano-cage. As a result, the Si_N Al₁₂N₁₁ is anticipated to be a potential novel sensor for detecting the presence of N₂H₄ molecule.     

Quantum chemical calculations of pristine and modified crystalline cellulose surfaces: benchmarking interactions and adsorption of water and electrolyte

In this study, we investigate the hydration of three different functional groups present on cellulose nanocrystal (CNC) surfaces: hydroxyls, carboxylates and sulphates by means of quantum chemical calculation. The performance of several density functional theory (DFT) functionals in reproducing, against higher level MP2 benchmark calculations, relevant non-covalent CNC interactions is also assessed. The effect of a sodium ion on the hydration of the surface functional groups was also investigated. Major restructuring of the hydrogen-bonding network within cellulose was found in the presence of a sodium ion. The calculated binding energy of water with a surface group ion pair was also greater, which indicates a greater hydrophilicity of CNC surfaces in the presence of adsorbed sodium. Cellulose hydrophilic surfaces (1 1 0) and (1 ?1 0) were also calculated using DFT methods. The results indicate that the surfaces possess different electrostatic potential maps. Hydrogen bond restructuring is found on the chemically modified surfaces. The adsorption energy of water and electrolyte is also found to be different on each surface.     

Density-functional study of oxygen adsorption on Mo(112)

Atomic oxygen adsorption on the Mo(112) surface has been investigated by means of first-principles total energy calculations. Among the variety of possible adsorption sites it was found that the bridge sites between two Mo atoms of the topmost row are favored for O adsorption at low and medium coverages. At about one monolayer coverage oxygen atoms prefer to adsorb in a quasithreefold hollow sites coordinated by two first-layer Mo atoms and one second layer atom. The stability of a structural model for an oxygen-induced p(2 x 3) reconstruction of the missing-row type is examined.     

Density-functional, density-functional tight-binding, and wave function calculations on biomolecular systems

Recently, two computational approaches that supply a density-functional-based quantum-chemical method with an empirical term accounting for London dispersion were introduced and found use in the studies of biomolecular systems, namely, DFT-D and SCC-DFTB-D. Here, we examine the performance and usability of these combined techniques for dealing with several tasks typically occurring in the research of biomolecules. The interaction energy of small biomolecular complexes agrees very well with the reference data yielded by correlated ab initio quantum chemical methods. In real-life studies aimed at interaction energy, structure, and infrared spectra, the mentioned methods provide results in good agreement with each other and with experiment (where available). The very favorable time demands of these approaches are discussed, and for each of them, a suitable area of use is proposed on the basis of the results of our analysis.     

First principle study of adsorption of boron-halogenated system on pristine graphyne

To ensure the possibility of using graphyne as a gas sensor, we have studied the adsorption of boron-halogenated system on pristine graphyne with the help of density functional theory using generalized gradient approximation. Depending on binding energy the most stable orientation, adsorption strength and optimal distance between the above mention molecules and graphyne surface have been determined. The band gap of graphyne slightly increases with the adsorption of the boron-halogenated system. The graphyne system behaves as n-type semiconductor when it interacts with BI₃ and BCl₃ molecules, and it behaves as p-type semiconductor when interaction with BF₃ molecule takes place. Our result reveals that the electronic properties of pristine graphyne are highly influenced by the adsorption of boron-halogenated molecule. We have observed that pristine graphyne has zero electric dipole moment, but with the interaction of boron-halogenated molecule, a significant change in the electric dipole moment takes place. Hence, by measuring the electric dipole moment change, graphyne-based gas sensor can be design for the detection of above-mentioned molecules.     

Density-functional generalized-gradient and hybrid calculations of electromagnetic properties using Slater basis sets

In this paper we extend our density-functional theory calculations, with generalized gradient approximation and hybrid functionals, using Slater-type orbitals (STOs), to the determination of second-order molecular properties. The key to the entire methodology involves the fitting of all STO basis function products to an auxiliary STO basis, through the minimization of electron-repulsion integrals. The selected properties are (i) dipole polarizabilities, (ii) nuclear magnetic shielding constants, and (iii) nuclear spin-spin coupling constants. In all cases the one-electron integrals involving STOs were evaluated by quadrature. The implementation for (ii) involved some complexity because we used gauge-including atomic orbitals. The presence of two-electron integrals on the right-hand side of the coupled equations meant that the fitting procedure had to be implemented. For (iii) in the hybrid case, fitting procedures were again required for the exchange contributions. For each property we studied a number of small molecules. We first obtained an estimate of the basis set limit using Gaussian-type orbitals (GTOs). We then showed how it is possible to reproduce these values using a STO basis set. For (ii) a regular TZ2P quality STO basis was adequate; for (i) the addition of one set of diffuse functions (determined by Slater's rules) gave the required accuracy; for (iii) it was necessary to add a set of 1s functions, including one very tight function, to give the desired result. In summary, we show that it is possible to predict second-order molecular properties using STO basis sets with an accuracy comparable with large GTO basis sets. We did not encounter any major difficulties with either the selection of the bases or the implementation of the procedures. Although the energy code (especially in the hybrid case) may not be competitive with a regular GTO code, for properties we find that STOs are more attractive.     

Density-functional theory calculations of optical rotatory dispersion in the nonresonant and resonant frequency regions

The complex linear response function, which can be employed for calculations of second-order molecular properties in regions of strong absorption, is here extended to encompass the mixed electric-dipole-magnetic-dipole polarizability. The mixed electric-dipole-magnetic-dipole polarizability determines the optical rotation and, when absorption is taken into account, the full anomalous optical rotatory dispersion (ORD) spectra of chiral molecules can be calculated using first-principle quantum-chemical methods. Gauge-origin independence of the results is ensured through the use of London atomic orbitals. To illustrate the importance of taking the absorption process properly into account, we here apply this methodology to the study of the anomalous ORD of hydrogen peroxide, 3R-methylcyclohexanone, 4R-1,1-dimethyl-[3]-(1,2)-ferrocenophan-2-on, and the D(2) isomer of the C(84) fullerene.     

掺杂碳纳米管对五氯酚吸附作用的理论研究

为了寻找检测高毒性、持久性有机污染物五氯酚(PCP)的新型材料,应用密度泛函理论研究了(8,0)和(5,5)单壁碳纳米管(SWCNT)以及相应的Si、B和N掺杂的SWCNT对PCP分子的吸附性能.计算结果表明,(8,0)和(5,5)SWCNT与PCP分子之间为物理吸附;Si原子掺杂(8,0)和(5,5)SWCNT,引起了碳纳米管掺杂部位六元环的畸变,增强了SWCNT的反应活性,掺杂后的SWCNT对PCP分子形成化学吸附,其几何结构和电子性质发生了显著变化;B和N原子掺杂的SWCNT对PCP分子的吸附没有明显增强.Si原子掺杂的SWCNT最有潜力用于检测PCP分子.     

Density-functional calculations of relativistic spin-orbit effects on nuclear magnetic shielding in paramagnetic molecules

Terms arising from the relativistic spin-orbit effect on both hyperfine and Zeeman interactions are introduced to density-functional theory calculation of nuclear magnetic shielding in paramagnetic molecules. The theory is a generalization of the former nonrelativistic formulation for doublet systems and is consistent to O(alpha4), the fourth power of the fine structure constant, for the spin-orbit terms. The new temperature-dependent terms arise from the deviation of the electronic g tensor from the free-electron g value as well as spin-orbit corrections to hyperfine coupling tensor A, the latter introduced in the present work. In particular, the new contributions include a redefined isotropic pseudocontact contribution that consists of effects due to both the g tensor and spin-orbit corrections to hyperfine coupling. The implementation of the spin-orbit terms makes use of all-electron atomic mean-field operators and/or spin-orbit pseudopotentials. Sample results are given for group-9 metallocenes and a nitroxide radical. The new O(alpha4) corrections are found significant for the metallocene systems while they obtain small values for the nitroxide radical. For the isotropic shifts, none of the three beyond-leading-order hyperfine contributions are negligible.     

DFT calculations on the catalytic oxidation of CO over Si-doped (6,0) boron nitride nanotubes

The oxidation of carbon monoxide (CO) is important for a series of technological and environmental applications. In this work, the catalytic oxidation of CO on Si-doped (6,0) boron nitride nanotubes (BNNTs) is investigated by using density functional theory calculations. Reaction barriers and corresponding thermodynamic parameters were calculated using the M06-2X, B3LYP and wB97XD density functionals with 6-31G* basis set. Our results indicate that a vacancy defect in BNNT strongly stabilizes the Si adatom and makes it more positively charged. This charging enhances the adsorption of reaction gases (O₂ and CO) and results in the change of the electronic structure properties of the tube. The calculated barrier of the reaction CO + O₂ → CO₂ + O_ads on Si-doped BNNTs following the Langmuir–Hinshelwood is lower than that on the traditional noble metal catalysts. The second step of the oxidation would be the Eley–Rideal reaction (CO + O_ads → CO₂) with an energy barrier of about 1.8 and 10.1 kcal/mol at M06-2X/6-31G* level. This suggests that the CO oxidation catalyzed by the Si-doped BNNTs is likely to occur at the room temperature. The results also demonstrate that the activation energies and thermodynamic quantities calculated by M06-2X, B3LYP and wB97XD functionals are consistent with each other.     

Effects of the HCN adsorption on the structural and electronic parameters of the beryllium oxide nanotube

The adsorption behavior of the HCN on the surface of beryllium oxide nanotube (BeONT) is studied by the density functional theory. Geometrical parameters, electronic properties and adsorption energies have been calculated for the BeONT and fourteen different HCN configurations on the nanotube. According to the obtained results, the process of the HCN molecule adsorption on different sites on the external surface of the nanotube is exothermic and all of the configurations are stable, while the process of HCN molecule adsorption on the internal surface of the BeONT is endothermic. The adsorption energy values indicate that the HCN molecule can be physically adsorbed on the surface of the BeONT. Furthermore, the HOMO–LUMO gap (Eg) of the BeONT decreases upon the HCN adsorption, resulting in the enhancement of the electrical conductivity. The AIM theory has been also utilized to analyze the properties of the bond critical points: their electron densities and their Laplacians. NBO analysis indicates that the HCN molecule can be adsorbed on the surface of the nanotube with a charge transfer from nanotube to HCN molecule. Due to the physisorption, NQR parameters of nanotube are also altered. In order to examine the deformation degree of the nanotube after HCN molecule adsorption, deformation energy is calculated, which indicates that no significant curvature in the geometry of the nanotubes is occurred when HCN adsorbs onto the surface of BeONT.     

Quantum calculations on the adsorption of halide ions on the noble metals

The interaction of halide ions with the three noble metals has been investigated using the B3LYP density functional method and the cluster model approximation. The results of calculations for the M—X⁻ and M₁₂—X⁻ (M = Cu, Ag, Au; X = F, Cl, Br, I) systems are presented. At the (100) surface, modeled in the present work by the M₁₂ cluster, all halide ions have been found to adsorb preferentially at the hollow site, followed by the bridge and by the top positions. The adsorption energy has been found to decrease when going from fluoride to iodide in both atom—ion and cluster—ion cases. The opposite trend is observed for the estimates of the charge transfer from the ions to the surface. When different metals are compared, the M₁₂—X⁻ interaction energies decrease in the order Au > Ag > Cu, but for the smaller ions some deviations from this line do appear. The relative values of the calculated harmonic vibrational frequencies do agree with those found experimentally, but their magnitude is much smaller as a result of the effect of the lower surface coverage.     

Regioselective competitive adsorption of water and organic vapor mixtures on pristine single-walled carbon nanotube bundles

Sequential adsorption of water and organic vapor mixtures onto single-walled carbon nanotube (SWNT) bundles is studied experimentally and by grand canonical Monte Carlo (GCMC) simulation to elucidate the distinct interactions between select adsorbates and the nanoporous structure of SWNTs. Experimental adsorption isotherms on SWNT bundles for hexane, methyl ethyl ketone, cyclohexane, and toluene individually mixed in carrier gases that were nearly saturated with water vapor are compared with the GCMC-simulated isotherms for hexane, as a representative organic, on the external surface of the heterogeneous SWNT bundles. From the nearly perfect overlap between the experimental and simulated isotherms, it is concluded that until near saturation only the internal pore volume of pristine SWNT bundles fills with water. The adsorption of water vapor on the peripheral surface of the bundles remains insignificant, if not negligible, in comparison to the adsorption of water in the internal volume of the bundles. This is in contrast with the adsorption of pure hexane, which exhibits appreciable adsorption both inside the bundles and on their external surface. It is also suggested that during competitive adsorption, water molecules take precedence over small nonpolar and polar organic molecules for adsorption inside SWNTs and leave unoccupied the hydrophobic external surface of the bundles for other more compatible adsorbates.     

Ab initio study of NH3 and H2O adsorption on pristine and Na-doped MgO nanotubes

We have investigated, on the basis of density functional theory calculations, the structural and electronic properties of chemical modification of pristine and Na-doped MgONTs with NH₃ and H₂O molecules. We found that the NH₃ and H₂O molecules can be barrierlessly adsorbed on the Mg atom of the tube sidewall along with a charge transfer from the adsorbate to MgONT. The adsorption is chemical in nature with adsorption energies about ?22.3 and ?21.5 kcal/mol for H₂O and NH₃, respectively. The calculated density of state (DOS) shows that the chemical modification of MgONTs with these molecules can be generally classified as certain type of “harmless modification.” In other words, the electronic properties of the MgONT are little changed by the adsorption processes. The substitution of an Mg atom in the tube surface with an Na atom results in a semi-insulator to p-type semiconductor transition based on DOS analysis. It was also found that the doping process reduces the adsorption energies and the electronic properties of Na-doped MgONT is slightly more sensitive toward NH₃ and H₂O molecules, compared with the pristine one.     

Lithium adsorption on graphite from density functional theory calculations

The structural, energetic, and electronic properties of the Li/graphite system are studied through density functional theory (DFT) calculations using both the local spin density approximation (LSDA), and the gradient-corrected Perdew-Burke-Ernzerhof (PBE) approximation to the exchange-correlation energy. The calculations were performed using plane waves basis, and the electron-core interactions are described using pseudopotentials. We consider a disperse phase of the adsorbate comprising one Li atom for each 16 graphite surface cells, in a slab geometry. The close contact between the Li nucleus and the graphene plane results in a relatively large binding energy (larger than 1.1 eV). A detailed analysis of the electronic charge distribution, density difference distribution, and band structures indicates that one valence electron is entirely transferred from the atom to the surface, which gives rise to a strong interaction between the resulting lithium ion and the cloud of pi electrons in the substrate. We show that it is possible to explain the differences in the binding of Li, Na, and K adatoms on graphite considering the properties of the corresponding cation/aromatic complexes.     

Electrostatic model calculations on multiple adsorption at NaCl surfaces

A previously proposed electrostatic model for physisorption at ionic solids is extended to multiple adsorption of small molecules. A new algorithm is developed to avoid interpenetration of the interacting systems. The geometry optimization procedure is described. Ab initio calculations are used for the application of the method to the adsorption of CO and CO₂ at NaCl(100) surfaces simulated by Na₂₅Cl₂₅ clusters. The orientation of the adsorbate molecules in dependence on the cumulative atomic multipole moments (CAMMs) of the cluster atoms is discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 685–693, 1997     

Divide-and-conquer calculations for clean surfaces and surface adsorption

The divide-and-conquer density-functional approach is implemented for electronic structure calculations of clean surfaces and surface adsorption. The method divides a semi-infinite solid-state system into subsystems and determines each subsystem density separately. We have applied the method to study two low index Li surfaces and the chemisorption of a monolayer of atomic hydrogen on the Li(100) surface. Surface and adsorption energies converge well with respect to the number of buffer atoms and surface layers. Our converged energies are in very good agreement with accurate theoretical and available experimental results. Received: 8 January 1997 / Accepted: 14 January 1997     

Pd金属表面CO吸附态的密度泛函计算及应用

通过对CO在Pd表面上形成的各种化学吸附态的理论计算,借助B3LYP／3—21G＊方法,确定了各种吸附态Pdn-CO（n=1-5,7,9）的优化几何构型、相对稳定性、反应活性和吸附性质。其中μ3-Pd,CO和μ4-Pd4CO比线式和桥式更易使CO活化,而且相对难解吸,表现出较好的催化性能。论文还就实验FT-IR谱峰,模拟了一些未见实验报道的吸附态,同时讨论了其稳定性和理论伸展振动频率。最后运用多组态相互作用（CASS-CF／3-21G＊）计算了主要吸附态的离解能,得到Pdn-CO较Pdn-OC稳定的结论。根据各吸附态的稳定性和对CO的活化程度,确定了桥式态IR吸收是实验跟踪反应的最佳吸收带。     

Nonempirical calculations of water adsorption on bridged structural fragments of aluminosilicate

Within the discussion of the possibility to apply semiempirical methods for chemisorption calculations, nonempirical calculations of two types of adsorption complexes of H₂O molecule with bridged structural fragments of aluminosilicate have been carried out.

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