Interaction of Small Gases with the Unsaturated Metal Centers of the HKUST‑1 Metal Organic Framework

The interactions of CO, CO₂, OCS, SO₂, NO, NO₂, N₂O, NH₃, PH₃, and other small molecules with the undercoordinated metal centers of the HKUST-1 metal organic framework are studied by means of density functional theory. These molecules are potentially harmful for humans and the environment and are widely studied because of their spectroscopic properties. In this work, the energetic and vibrational characteristics of the adsorbed species are calculated. Adsorption energies on the Cu²⁺ sites of the paddlewheel have been calculated, and the order is: NH₃ > H₂O > PH₃ > H₂S > SO₂ > CO ∼ OCS ∼ CO₂ ∼ N_<i>y</i>O_<i>x</i> > N₂ > O₂. The results show that the interactions can be classified into three categories: (1) weak physisorption, (2) polarization and electrostatics, and (3) strong acid–base. Moreover, interesting vibrational properties are calculated especially for carbonyl sulfide and dinitrogen monoxide, which can be bound via two different configurations on the metal atoms. The vibrational modes are shifting in different directions depending on the binding way of the molecule; e.g., the symmetric stretching of OCS is shifted by +17 or −16 cm^–1 when bound via the oxygen or the sulfur atom, respectively

Interaction of Biologically Important Organic Molecules with the Unsaturated Copper Centers of the HKUST‑1 Metal–Organic Framework: an Ab-Initio Study

Metal–organic frameworks (MOFs) provide new possibilities for their potential use in catalysis, gas storage/separation, and drug delivery. In this work, a computational study is performed on the interaction of biologically important organic molecules such as caffeine, urea, niacin, and glycine with the undercoordinated copper centers of the HKUST-1 MOF. Density functional theory calculations are used to identify the adsorption sites of the organic molecules in HKUST-1 and to calculate their interaction energies. Two types of interactions are calculated: (i) strong binding via their nitrogen or oxygen atoms with the copper atoms of the paddlewheel and (ii) hydrogen bonds with the carboxylate groups of the MOF. Certain molecules such as caffeine and niacin can interact simultaneously with more than two paddlewheels, thus making the interactions even stronger. The interaction energies vary from 75 kJ mol^–1 for glycine to 200 kJ mol^–1 for caffeine. The confinement of the guest molecules in the cage windows of the framework can also create strong interactions. To take into account the effect of coordination with multiple paddlewheels, a very large model of the HKUST-1 needs to be used. The numbers of (i) copper sites interacting with the guest molecule and (ii) hydrogen bonds between the carboxylate groups of the MOF and the guests have a major impact on binding strength. This is important information when applying rational design to create new MOFs that should serve as drug carriers

ADS2 lesson02 conceptual design of structures

We investigated computationally the α-, γ-, and β-isomeric structures, relative stabilities, and the electronic and basicity properties of magnetic [V^IV₁₄E₈O₅₀]^12– (hereafter referred to as <b>{<b>V₁₄E₈</b>}</b>) heteropolyoxovanadates (heteroPOVs) and their heavier chalcogenide-substituted [V^IV₁₄E₈O₄₂X₈]^12– (<b>{<b>V₁₄E₈X₈</b>}</b>) derivatives for E = Si^IV, Ge^IV, and Sn^IV and X = S, Se, and Te. We used density functional theory (DFT) with scalar relativistic corrections in combination with the conductor-like screening model of solvation. The main purpose of this investigation is to introduce the structure–property relations in heteroPOVs as well as to assist the synthesis and molecular deposition of these molecular vanadium-oxide spin clusters on surfaces. “Fully-reduced” polyoxoanions <b>{<b>V₁₄E₈</b>}</b> and <b>{<b>V₁₄E₈X₈</b>}</b> are virtually comprised of [V^IV₁₄O₃₈]^20– {V₁₄} skeletons of different symmetries, that is, <i>D</i>_2<i>d</i> for α-, <i>D</i>₂ for γ-, and <i>D</i>_4<i>h</i> for β-isomers, which are stabilized by the four {E₂O₃}²⁺ and four {E₂OX₂}²⁺ moieties, respectively. Our DFT calculations reveal stability trends α > γ > β for polyoxoanions <b>{<b>V₁₄E₈</b>}</b> and <b>{<b>V₁₄E₈X₈</b>}</b>, based on relative energies and HOMO–LUMO energy gaps. The α-isomeric polyoxoanions <b>{<b>V₁₄E₈</b>}</b> and <b>{<b>V₁₄E₈X₈</b>}</b> with the high negative net charges may easily pick up protons at the terminal E–O_t and E–X_t sites, respectively, which is evidenced by strongly negative enthalpies of monoprotonation. Energetically favorable sites on polyoxoanions α-<b>{<b>V₁₄E₈</b>}</b> and α-<b>{<b>V₁₄E₈X₈</b>}</b> for electrostatic pairing with countercations were also determined. Among β and γ isomers, the hitherto unknown γ-[V₁₄Sn₈O₅₀]^12– and γ-[V₁₄Sn₈O₄₂S₈]^12– seem to be the most viable targets for isolation. Furthermore, these Sn-substituted polyoxoanions are of high interest for electrochemical studies because of their capability to act as two-electron redox catalysts

Interaction of Small Gases with the Unsaturated Metal Centers of the HKUST‑1 Metal Organic Framework

The interactions of CO, CO₂, OCS, SO₂, NO, NO₂, N₂O, NH₃, PH₃, and other small molecules with the undercoordinated metal centers of the HKUST-1 metal organic framework are studied by means of density functional theory. These molecules are potentially harmful for humans and the environment and are widely studied because of their spectroscopic properties. In this work, the energetic and vibrational characteristics of the adsorbed species are calculated. Adsorption energies on the Cu²⁺ sites of the paddlewheel have been calculated, and the order is: NH₃ > H₂O > PH₃ > H₂S > SO₂ > CO ∼ OCS ∼ CO₂ ∼ N_<i>y</i>O_<i>x</i> > N₂ > O₂. The results show that the interactions can be classified into three categories: (1) weak physisorption, (2) polarization and electrostatics, and (3) strong acid–base. Moreover, interesting vibrational properties are calculated especially for carbonyl sulfide and dinitrogen monoxide, which can be bound via two different configurations on the metal atoms. The vibrational modes are shifting in different directions depending on the binding way of the molecule; e.g., the symmetric stretching of OCS is shifted by +17 or −16 cm^–1 when bound via the oxygen or the sulfur atom, respectively

Single-Layer Tl₂O: A Metal-Shrouded 2D Semiconductor with High Electronic Mobility

The first metal-shrouded two-dimensional semiconductor, single-layer Tl₂O, is discussed from first principles. It is thermally and dynamically stable, has a low cleavage energy calling for exfoliation from layered Tl₂O bulk, and has a very small interface mismatch compared to (001) Tl metal. Single-layer Tl₂O exhibits a direct bandgap of 1.56 eV and a very high charge carrier mobility of 4.3 × 10³ cm² V^–1 s^–1. The metal-shrouded 2D semiconductor promises interesting applications in 2D electronics. An intriguing layer-thickness-dependent direct-to-indirect bandgap transition is observed, and contrary to early literature, the bulk is also a semiconductor

DFTB Parameters for the Periodic Table, Part 2: Energies and Energy Gradients from Hydrogen to Calcium

In the first part of this series, we presented a parametrization strategy to obtain high-quality electronic band structures on the basis of density-functional-based tight-binding (DFTB) calculations and published a parameter set called QUASINANO2013.1. Here, we extend our parametrization effort to include the remaining terms that are needed to compute the total energy and its gradient, commonly referred to as repulsive potential. Instead of parametrizing these terms as a two-body potential, we calculate them explicitly from the DFTB analogues of the Kohn–Sham total energy expression. This strategy requires only two further numerical parameters per element. Thus, the atomic configuration and four real numbers per element are sufficient to define the DFTB model at this level of parametrization. The QUASINANO2015 parameter set allows the calculation of energy, structure, and electronic structure of all systems composed of elements ranging from H to Ca. Extensive benchmarks show that the overall accuracy of QUASINANO2015 is comparable to that of well-established methods, including PM7 and hand-tuned DFTB parameter sets, while coverage of a much larger range of chemical systems is available

Пропаганда во время Второй мировой войны: сравнительно-исторический анализ на примере некоторых визуальных источников

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GeP₃: A Small Indirect Band Gap 2D Crystal with High Carrier Mobility and Strong Interlayer Quantum Confinement

We propose a two-dimensional crystal that possesses low indirect band gaps of 0.55 eV (monolayer) and 0.43 eV (bilayer) and high carrier mobilities similar to those of phosphorene, GeP₃. GeP₃ has a stable three-dimensional layered bulk counterpart, which is metallic and known from experiment since 1970. GeP₃ monolayer has a calculated cleavage energy of 1.14 J m^–2, which suggests exfoliation of bulk material as viable means for the preparation of mono- and few-layer materials. The material shows strong interlayer quantum confinement effects, resulting in a band gap reduction from mono- to bilayer, and then to a semiconductor–metal transition between bi- and triple layer. Under biaxial strain, the indirect band gap can be turned into a direct one. Pronounced light absorption in the spectral range from ∼600 to 1400 nm is predicted for monolayer and bilayer and promises applications in photovoltaics

Detailed Atomistic Investigation of Fe-Doped Rutile Phases

We have investigated iron-doped rutile TiO₂ in great detail by density functional theory (DFT) calculations. The influence of the Fe dopants on the structural and electronic properties are calculated. Three different dopant models are considered in this study, where iron is present in Fe­(II), Fe­(III), and Fe­(IV) oxidation states. Our results indicate that the configuration of Fe­(III), where two neighboring Ti sites are replaced by Fe dopants and an O vacancy locates in between, is the lowest-energy structure. The resulting Mößbauer signatures are in excellent agreement with the available experimental literature data, thus supporting the proposed structural model. Although the crystal structure of doped rutile is not significantly altered, even for larger concentrations of dopant atoms, the local structure around Fe atoms can be strongly distorted, especially due to the presence of oxygen vacancies. Fe doping lowers the band gap and introduces midgap states

Electromechanical Properties of Carbon Nanotubes

Electromechanical properties of carbon nanotubes were studied using Born–Oppenheimer molecular dynamics simulations within the QM/MM approach. The indentation of nanotubes was simulated using an AFM tip. The electronic structure and transport response to the mechanical deformations were investigated for different deflection points starting from perfect unperturbed systems up to the point where the first bonds break. We found the dependence of the force constant on the diameter size: the smaller the diameter, the larger the <i>k</i>. For the metallic-armchair tubes, with diameters from 8 to 13 Å, the conductance decreases only slightly under radial deformation, and a tiny band gap opening of up to 50 meV was observed