Search Results (18)

Alongside the gradual progress of industrialization and the continuous development of human society, the problems of environmental pollution and energy crisis have become increasingly prominent. Semiconductor photocatalysis is a promising solution to these challenges. The photocatalytic reduction of CO₂ by TiO₂ to produce carbon monoxide and methane is a process which has been identified as a means of developing clean energy. In this paper, two-dimensional TiO₂ (2D-TiO₂) was synthesized via a one-step solvothermal method, and one-dimensional TiO₂ (1D-TiO₂) was obtained through a hydrothermal process. Their photocatalytic CO₂ reduction performances were systematically investigated. The results show that 2D-TiO₂ exhibits superior catalytic activity compared to 1D-TiO₂, which can be attributed to its lamellar structure, larger specific surface area, and improved hydrophilicity, providing more active sites and faster reaction kinetics. To further reveal the reaction mechanism, density functional theory (DFT) calculations were carried out using VASP with the GGA–PBE functional, PAW potentials, and a plane-wave cutoff energy of 520 eV. A 3 × 3 × 1 Monkhorst–Pack grid was used for Brillouin zone integration, and all possible adsorption configurations of CO₂*, COOH*, and CO* intermediates on the 2D-TiO₂ surface were evaluated. The results confirm that 2D-TiO₂ stabilizes key intermediates more effectively, thereby lowering the energy barrier and facilitating CO₂ reduction. These findings demonstrate that structural modulation of TiO₂ significantly influences its photocatalytic performance and highlight the great potential of 2D-TiO₂ for efficient CO₂ conversion and clean energy applications. Full article

The fundamental chemistries and electronic structures of platinum catalysts over nitrogen-doped carbon supports were examined to determine the subtle yet important roles graphitic defect-based and pyridinic defect-based nitrogen defects have in stabilizing platinum. These roles address and extend previously gathered incomplete knowledge of how combinations of graphitic defect and pyridinic defect affect the local electronic structure, leading to a greater unified understanding of platinum stability. A theoretical study was designed where different atomically sized platinum clusters were investigated over seven different nitrogen defect combinations on graphene carbon support. Differently sized platinum clusters offered parametric insights into the differences in metal–support interactions. Full article

To meet the demands for functional layers in inverted flexible perovskite solar cells, high-performance formamidinium-based perovskite solar cells, and high-performance photodetectors in future applications, it is crucial to appropriately reduce the bandgap of third-generation wide-bandgap semiconductor materials. In this study, we first optimized doping sites through Ag-Cl and Ag-S configurations to establish stable substitution patterns, followed by density functional theory (DFT) calculations using the Generalized Gradient Approximation with the Perdew–Burke–Ernzerhof (GGA-PBE) functional, implemented in the Vienna Ab initio Simulation Package (VASP). A plane-wave basis set with a cutoff energy of 450 eV and a 3 × 4 × 3 Γ-centered k-mesh were adopted to investigate the effects of Mg-Cl, Mg-S, Zn-Cl, and Zn-S co-doping on the structural stability, electronic properties, and optical characteristics of β-Ga₂O₃. Based on structural symmetry, six doping sites were considered, with Ag-S/Cl systems revealing preferential occupation at octahedral Ga(1) sites through site formation energy analysis. The results demonstrate that Mg-Cl, Mg-S, Zn-Cl, and Zn-S co-doped systems exhibit thermodynamic stability. The bandgap of pristine β-Ga₂O₃ was calculated to be 2.08 eV. Notably, Zn-Cl co-doping achieves the lowest bandgap reduction to 1.81 eV. Importantly, all co-doping configurations, including Mg-Cl, Mg-S, Zn-Cl, and Zn-S, effectively reduce the bandgap of β-Ga₂O₃. Furthermore, the co-doped systems show enhanced visible light absorption (30% increase at 500 nm) and improved optical storage performance compared to the pristine material. Full article

Diradical character is one of the characteristic quantities of functional open-shell molecules. Prof. Nakano devotedly studied the relationship between diradical character and material properties of open-shell molecules; now, we can use the diradical character as a powerful tool for molecular material designs. It is still unclear how the open-shell molecules are affected by the interaction with the surface although the molecules have been immobilised for device applications. In the present study, the adsorptions of model diradical molecules with s-electrons on the MgO (001) and BaO (001) surfaces are investigated using approximate spin projected density functional theory with plane-wave basis (AP-DFT/plane-wave) to provide a systematic discussion of surface–diradical interactions. The accuracy of AP-DFT/plane-wave was verified by comparisons with the calculated results by NEVPT2. The computational error introduced by DFT calculations on the diradical state (spin contamination error) is reduced by the surface–diradical interaction. In addition, it is shown that (1) the diradical character is amplified by the orbital polarisation effects of oxide ions, and (2) the character decreases when the magnetic orbitals become electron-rich due to electron donation from the surfaces. The two effects are competing; the former is pronounced in Au systems, whereas the latter is pronounced in Ag systems. Full article

The tetrafluoroborate salt of the cationic Cu(I) complex [Cu(CHpz₃)(PPh₃)]⁺, where CHpz₃ is the tridentate N-donor ligand tris(pyrazol-1-yl)methane and PPh₃ is triphenylphosphine, was synthesized through a displacement reaction on the acetonitrile complex [Cu(NCCH₃)₄][BF₄]. The compound crystallizes in the monoclinic P2₁/c space group. The single-crystal X-ray diffraction revealed that the copper(I) centre is tetracoordinated, with a disposition of the donor atoms surrounding the metal centre quite far from the ideal tetrahedral geometry, as confirmed by continuous shape measures and by the τ₄ parameter. The intermolecular interactions at the solid state were investigated through the Hirshfeld surface analysis, which highlighted the presence of several non-classical hydrogen bonds involving the tetrafluoroborate anion. The electronic structure of the crystal was modelled using plane-wave DFT methods. The computed band gap is around 2.8 eV and separates a metal-centred valence band from a ligand-centred conduction band. NMR spectroscopy indicated the fluxional behaviour of the complex in CDCl₃ solution. The geometry of the compound in the presence of chloroform as implicit solvent was simulated by means of DFT calculations, together with possible mechanisms related to the fluxionality. The reversible dissociation of one of the pyrazole rings from the Cu(I) coordination sphere resulted in an accessible process. Full article

We have developed a highly efficient computation method based on density functional theory (DFT) within a set of fully symmetrized basis functions for the C₆₀ buckyball, which possesses the icosahedral ($I_h$) point-group symmetry with 120 symmetry operations. We demonstrate that our approach is much more efficient than the conventional approach based on three-dimensional plane waves. When applied to the calculation of optical transitions, our method is more than one order of magnitude faster than the existing DFT package with a conventional plane-wave basis. This makes it very convenient for modeling optical and transport properties of quantum devices related to buckyball crystals. The method introduced here can be easily extended to other fullerene-like materials. Full article

Fe[C₅H₅N]₂[N(CN)₂]₂ (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)₂ and FeCl₂·4H₂O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in the monoclinic space group I2/m (no. 12), different from Mn[C₅H₅N]₂[N(CN)₂]₂ (P2₁/c, no. 14) due to tilted pyridine rings, with a = 7.453(7) Å, b = 13.167(13) Å, c = 8.522(6) Å, β = 114.98(6)° and Z = 2. ATR-IR, AAS, and CHN measurements confirm the presence of dicyanamide and pyridine. Thermogravimetric analysis shows that π-stacking interactions of the pyridine rings play an important role in structural stabilization. Based on DFT-optimized structures, a chemical bonding analysis was performed using a local-orbital framework by projection from a plane-wave basis. The resulting bond orders and atomic charges are in good agreement with the expectations based on the structure analysis. SQUID magnetic susceptibility measurements show a high-spin state Fe^II compound with predominantly antiferromagnetic exchange interactions at lower temperatures. Full article

Kaolinite is one of the principal rare earth element (REE) ion-adsorption clays that hosts a wide range of elements, including Dy(III) as a representative example. Ammonium sulfate is a typical salt used to leach REEs. Due to the carbon dioxide emissions which occur during ammonia production, it is urgently necessary to develop low environmental pollution leaching agents that can replace (NH₄)₂SO₄. MgSO₄ is regarded as the most promising eco-friendly leaching agent. Herein, the first-principles plane-wave pseudopotential method based on the density functional theory (DFT) was used to investigate the stable adsorption structures of Dy(III) and its hydrated ions, MgSO₄ leaching agent ions and the corresponding hydrated ions on the surface of kaolinite, which revealed the adsorption mechanism of Dy(III), Mg(II), and SO₄²⁻ on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite. Based on the research results of the steric hindrance effect of Dy(III) on the silico–oxygen plane and the aluminum–hydroxyl plane of kaolinite, the adsorption of Dy(H₂O)₁₀³⁺ was more stable on the silico–oxygen plane. It was easier to leach out Dy(III) with MgSO₄, while SO₄²⁻ tended to interact with the rare earth ions in an aqueous solution. The results provide theoretical guidance for efficient rare earth extraction and obtaining novel efficient leaching agents. Full article

Many areas of electronics, engineering and manufacturing rely on ferromagnetic materials, including iron, nickel and cobalt. Very few other materials have an innate magnetic moment rather than induced magnetic properties, which are more common. However, in a previous study of ruthenium nanoparticles, the smallest nano-dots showed significant magnetic moments. Furthermore, ruthenium nanoparticles with a face-centred cubic (fcc) packing structure exhibit high catalytic activity towards several reactions and such catalysts are of special interest for the electrocatalytic production of hydrogen. Previous calculations have shown that the energy per atom resembles that of the bulk energy per atom when the surface-to-bulk ratio < 1, but in its smallest form, nano-dots exhibit a range of other properties. Therefore, in this study, we have carried out calculations based on the density functional theory (DFT) with long-range dispersion corrections DFT-D3 and DFT-D3-(BJ) to systematically investigate the magnetic moments of two different morphologies and various sizes of Ru nano-dots in the fcc phase. To confirm the results obtained by the plane-wave DFT methodologies, additional atom-centred DFT calculations were carried out on the smallest nano-dots to establish accurate spin-splitting energetics. Surprisingly, we found that in most cases, the high spin electronic structures had the most favourable energies and were hence the most stable. Full article

Adsorption mineralization of gold is an important mineralization mechanism under epigenetic and low temperature conditions. In this paper, a plane-wave pseudopotential method based on density functional theory (DFT) is used to explore the adsorption mechanism of gold on the surface of pyrite. Among the three surfaces of pyrite, the surface energies of (100), (111), and (210) surfaces are 1.0508, 1.5337, and 1.8255 J∙m², respectively, and the (100) surface is the most stable surface in the thermodynamic state. The adsorption capacities of gold atoms under different surfaces are (210) (−2.68 eV) > (111) (−1.67 eV) > (100) (−0.84 eV). Mulliken analysis indicates that charge transfer occurs after the adsorption of gold atoms onto the surface of pyrite (210), and gold and iron atoms are oxidized with the reduction of sulfur atoms. The density of states (PDOS) analysis shows that the 5d orbital on the Fermi energy level of the iron atom is active and the adsorption capacity is greater than that of the sulfur atom, and adsorption is formed between the gold atom, which leads to the gold being able to be stably deposited on the surface of pyrite (210). Full article

In this work, we used, for the first time, a computational Self-Consistent Field procedure based on plane waves to describe the low and high spin conformational states of the complex [Fe(bpy)₃]^2+. The results obtained in the study of the minimum energy structures of this complex, a prototype of a wide class of compounds called Spin Cross Over, show how the plane wave calculations are in line with the most recent studies based on gaussian basis set functions and, above all, reproduce within acceptable errors the experimental spectra of X-ray absorption near-edge structure spectroscopy (XANES). This preliminary study shows the capabilities of plane wave methods to correctly describe the molecular structures of metal-organic complexes of this type and paves the way for future even complex computational simulations based on the energy gradient, such as Nudge Elastic Band or ab-initio Born-Oppenheimer molecular dynamics. Full article

Alamethicin (ALM) is an antimicrobial peptide that is frequently employed in studies of the mechanism of action of pore-forming molecules. Advanced techniques of solid-state NMR spectroscopy (SSNMR) are important in these studies, as they are capable of describing the alignment of helical peptides, such as ALM, in lipid bilayers. Here, it is demonstrated how an analysis of the SSNMR measurements can benefit from fully periodic calculations, which employ the plane-wave density-functional theory (PW DFT) of the solid-phase geometry and related spectral parameters of ALM. The PW DFT calculations are used to obtain the structure of desolvated crystalline ALM and predict the NMR chemical shift tensors (CSTs) of its nuclei. A variation in the CSTs of the amidic nitrogens and carbonyl carbons along the ALM backbone is evaluated and included in simulations of the orientation-dependent anisotropic ¹⁵N and ¹³C chemical shift components. In this way, the influence of the site-specific structural effects on the experimentally determined orientation of ALM is shown in models of cell membranes. Full article

A dodecadepsipeptide valinomycin (VLM) has been most recently reported to be a potential anti-coronavirus drug that could be efficiently produced on a large scale. It is thus of importance to study solid-phase forms of VLM in order to be able to ensure its polymorphic purity in drug formulations. The previously available solid-state NMR (SSNMR) data are combined with the plane-wave DFT computations in the NMR crystallography framework. Structural/spectroscopical predictions (the PBE functional/GIPAW method) are obtained to characterize four polymorphs of VLM. Interactions which confer a conformational stability to VLM molecules in these crystalline forms are described in detail. The way how various structural factors affect the values of SSNMR parameters is thoroughly analyzed, and several SSNMR markers of the respective VLM polymorphs are identified. The markers are connected to hydrogen bonding effects upon the corresponding (¹³C/¹⁵N/¹H) isotropic chemical shifts of (C_O, N_amid, H_amid, H_α) VLM backbone nuclei. These results are expected to be crucial for polymorph control of VLM and in probing its interactions in dosage forms. Full article

Reliable values of the solid-state NMR (SSNMR) parameters together with precise structural data specific for a given amino acid site in an oligopeptide are needed for the proper interpretation of measurements aiming at an understanding of oligopeptides’ function. The periodic density functional theory (DFT)-based computations of geometries and SSNMR chemical shielding tensors (CSTs) of solids are shown to be accurate enough to support the SSNMR investigations of suitably chosen models of oriented samples of oligopeptides. This finding is based on a thorough comparison between the DFT and experimental data for a set of tripeptides with both ¹³C_α and ¹⁵N_amid CSTs available from the single-crystal SSNMR measurements and covering the three most common secondary structural elements of polypeptides. Thus, the ground is laid for a quantitative description of local spectral parameters of crystalline oligopeptides, as demonstrated for the backbone ¹⁵N_amid nuclei of samarosporin I, which is a pentadecapeptide (composed of five classical and ten nonproteinogenic amino acids) featuring a strong antimicrobial activity. Full article

Density functional theory (DFT) calculations are employed to explore and assess the effects of the relativistic spin–orbit interaction and electron correlations in the actinide elements. Specifically, we address electron correlations in terms of an intra-atomic Coulomb interaction with a Hubbard U parameter (DFT + U). Contrary to recent beliefs, we show that for the ground-state properties of the light actinide elements Th to Pu, the DFT + U makes its best predictions for U = 0. Actually, our modeling suggests that the most popular DFT + U formulation leads to the wrong ground-state phase for plutonium. Instead, extending DFT and the generalized gradient approximation (GGA) with orbital–orbital interaction (orbital polarization; OP) is the most accurate approach. We believe the confusion in the literature on the subject mostly originates from incorrectly accounting for the spin–orbit (SO) interaction for the p_1/2 state, which is not treated in any of the widely used pseudopotential plane-wave codes. Here, we show that for the actinides it suffices to simply discard the SO coupling for the p states for excellent accuracy. We thus describe a formalism within the projector-augmented-wave (PAW) scheme that allows for spin–orbit coupling, orbital polarization, and non-collinear magnetism, while retaining an efficient calculation of Hellmann–Feynman forces. We present results of the ground-state phases of all the light actinide metals (Th to Pu). Furthermore, we conclude that the contribution from OP is generally small, but substantial in plutonium. Full article