The nature of structure and bonding between transition metal and mixed Si-Ge tetramers: A 20-electron superatom system

Computational study of oxidation mechanism of mineral green pigments

The molecular structures, electronic properties, and the UV-vis absorption spectra of the oxides of mineral green pigment (MGP) have been theoretically calculated by using the density-functional theory (DFT) method. Our results reveal that the ground-state structure (isomer-I) of the oxides takes on an O-bridged bond with the polycyclic ring. The chemical stabilities of the oxides (I-V) are gradually reduced, of which the I isomer has the largest gap (2.50 eV). Moreover, the adsorption of the two oxygen atoms tailors the electronic structures of oxides, and the electronic properties are keys to understand the structural stabilization of the complexes. Additionally, the strongest UV-vis absorption band of the I isomer has been assigned; e.g., the crucial excitation originates from a HOMO-17→LUMO (32%) transition at ~ 187.3 nm.

Modified Lennard-Jones potentials for nanoscale atoms

A classical 6-12 Lennard-Jones (LJ) equation has been widely used to model materials and is the potential of choice in studies when the focus is on fundamental issues. Here we report a systematic study comparing the pair interaction potentials within solid-state materials (i.e., [Co₆ Se₈ (PEt₃ )₆ ][C₆₀ ]₂ , [Cr₆ Te₈ (PEt₃ )₆ ][C₆₀ ]₂ , [Ni₉ Te₆ (PEt₃ )₈ ][C₆₀ ]) using density functional theory (DFT) calculations and LJ parametrization. Both classical (6-12 LJ) and modified LJ (mLJ) models were developed. In the mLJ approach, the exponents 6 and 12 are replaced by different integer number n and 2n, respectively, and an additional parameter (α) is introduced to describe intermolecular distance shift arising within the geometric centers' approach (instead of the shortest interatomic distance between particles). A general LJ approach reexamination reveals that in the case of nanoatoms, the attractive term decays with distance as the inverse fourth power, and the dominating at short distances repulsive term decays as the inverse eighth power. The modification of the LJ equation is even more prominent for interaction profiles, where intermolecular distance corresponds to separation between geometric centers of particles. In this approach, the attractive term decays with distance as the inverse 12th power, while the repulsive term decays rapidly (as the inverse 24th power). Thus, the mLJ models (e.g., 4-8 LJ) rather than the 6-12 classical ones seem to be a better choice for the description of binary interactions of nanoatoms. The developed mLJ models and electronic structure characteristics give an insight into the explanation of the unique physicochemical properties of superatomic-based solid-state materials.

Structural and electronic properties of nanosize semiconductor HfSin0/-/2- (n = 6-16) material: a double-hybrid density functional theory investigation

Equilibrium geometries, thermodynamic stabilities, chemical reactivities, and electronic properties of neutral, mono-, and di-anionic Hf-doped silicon nanoclusters HfSi_n^0/-2- (n = 6-16) are calculated by employing an ABCluster global search technique combined with mPW2PLYP scheme. Based on the concordance between simulated and experimental PES, the true global minima are confirmed for n = 6, 9, and 12-16. Optimized geometries for neutral HfSi_n nanoclusters can be divided into three stages: first, Hf atom prefers locating on the surface site of the cluster for n = 6-9, which can be obtained by adding one, two, three, and four Si atoms to HfSi₅ tetragonal bipyramid, respectively (denoted as additive type); then, Hf atom is surrounded by Si atoms with half-cage configuration for n = 10-13; finally, Hf atom is encapsulated into Si cage pattern for n = 14-16. For mono-anions, it is from additive type (n = 6-11) to the cagelike configuration with Hf atom resided in silicon clusters (n = 12-16). For di-anions, it is additive type (n = 6-9) to the Hf-linked configuration (n = 10-11), and in the end to the Hf-encapsulated cagelike motif (n = 12-16). The thorough analysis of stability and chemical bonding revealed that the neutral HfSi₁₆ and di-anionic HfSi₁₅^2- are magic nanoclusters with good thermodynamic and chemical stability, which may make them as the most suitable building block for new functional materials. We suggest that the experimental PES of HfSi_n^- with n = 7, 8, 10, and 11 should be further examined due to the lack of comparably low electron binding energy peaks.

Open-shell jellium aromaticity in metal clusters

The 2N2 + 2N + 1 with S = N + 1/2 rule represented the extension to open-shell spherical compounds of the 2(N + 1)2 Hirsch rule for spherical aromatic species. In this work, we provide evidence that the jellium model with its magic numbers can also be extended to open-shell half-filled systems.

Effects of correlations and temperature on the electronic structures and related physical properties of FeSi and CoSi: a comprehensive study

Here, we report detailed investigations of the temperature dependent (100-800 K) electronic structures of FeSi and CoSi by using a DFT+DMFT method where self-consistently calculated values of U and J are used. The calculated spectral functions are found to provide fairly good representation for the experimentally observed photoemission spectra for both the compounds. For FeSi, the density of states (DOS) closer to the Fermi level are found to increase with the increase in temperature up to 450 K and then they decrease, whereas, for CoSi DOS continuously decrease with an increase in temperature. The electronic states of FeSi are greatly influenced by electronic correlations while they are moderately influenced in CoSi. From momentum resolved spectral functions, the excitations have shown enhanced broadening with temperature rise in FeSi whereas an opposite behavior is observed in CoSi. In FeSi, the maximum effect of temperature on the lifetime of [Formula: see text] quasiparticles states is observed where it first decreases to 400 K and then increases, and finally becomes almost infinite at 800 K. The temperature dependent behavior of DOS and quasiparticle lifetime help us in understanding the experimentally observed electrical resistivity and Seebeck coefficient for these compounds. The calculated effective magnetic moment [Formula: see text] for Fe (∼2.5 [Formula: see text], which is closer to the experimental value) is temperature independent. The electronic structures of these compounds are showing the existence of mixed configurations with [Formula: see text] and [Formula: see text] for FeSi and CoSi, respectively. Average electrons in the d orbitals are found as  ∼6.5 and  ∼7.7 for FeSi and CoSi, respectively, with charge fluctuations [Formula: see text] 0.9 are obtained for both materials. This suggests that both the compounds are lying in the intermediate coupling regime of electronic correlations.

Structural, electronic and spectral properties of carborane-containing boron dipyrromethenes (BODIPYs): A first-principles study

In this work, we reported the geometrical structures, electronic and spectral properties of the carborane-containing BODIPYs complexes using the density functional theory calculations. In two structures, the calculated main bond lengths and bond angels of structural framework are consistent with X-ray experiment, and the two BODIPYs complexes are thermodynamically and kinetically stable. The strongest DOS band is mainly dominated by the BB and BH σ-bonds of carborane fragment, whereas the π-type MOs on the pyrromethene fragment contribute to the high-energy DOS bands. Analysis of the AdNDP chemical bonding indicates that the carborane cage can be stabilized by eleven delocalized 3c2e and two delocalized 4c2e σ-bonds, while the pyrromethene fragment corresponds to five delocalized 3c2e π-bonds. In addition, the main characteristic peaks of the two simulated IR spectra for the BODIPYs complexes are properly assigned. Hopefully, all these results will be helpful for understanding the electronic structures, and further stimulate the study on the biological and medical applications.

Effect of Alkali Metal Atoms Doping on Structural and Nonlinear Optical Properties of the Gold-Germanium Bimetallic Clusters

A new series of alkali-based complexes, AM@Ge_nAu (AM = Li, Na, and K), have been theoretically designed and investigated by means of the density functional theory calculations. The geometric structures and electronic properties of the species are systematically analyzed. The adsorption of alkali metals maintains the structural framework of the gold-germanium bimetallic clusters, and the alkali metals prefer energetically to be attached on clusters’ surfaces or edges. The high chemical stability of Li@Ge₁₂Au is revealed by the spherical aromaticity, the hybridization between the Ge atoms and Au-4d states, and delocalized multi-center bonds, as well as large binding energies. The static first hyperpolarizability (β_tot) is related to the cluster size and geometric structure, and the AM@Ge_nAu (AM = Na and K) clusters exhibit the much larger β_tot values up to 13050 a.u., which are considerable to establish their strong nonlinear optical (NLO) behaviors. We hope that this study will promote further application of alkali metals-adsorbed germanium-based semiconductor materials, serving for the design of remarkable and tunable NLO materials.

First-Principles Study of Structural, Electronic and Magnetic Properties of Metal-Centered Tetrahexahedral V15⁺ Cluster

The V-centered bicapped hexagonal antiprism structure (A), as the most stable geometry of the cationic V₁₅⁺ cluster, is determined by using infrared multiple photo dissociation (IR-MPD) in combination with density functional theory computations. It is found that the A structure can be stabilized by 18 delocalized 3c-2e σ-bonds on outer V₃ triangles of the bicapped hexagonal antiprism surface and 12 delocalized 4c-2e σ-bonds on inner trigonal pyramidal V₄ moiety, and the features are related to the strong p-d hybridization of the cluster. The total magnetic moments on the cluster are predicted to be 2.0 µ_B, which come mainly from the central vanadium atom.

The structural and electronic properties of NbSin-/0 (n = 3-12) clusters: anion photoelectron spectroscopy and ab initio calculations

Niobium-doped silicon clusters, NbSi_n^- (n = 3-12), were generated by laser vaporization and investigated by anion photoelectron spectroscopy. The structures and electronic properties of NbSi_n^- anions and their neutral counterparts were investigated with ab initio calculations and compared with the experimental results. It is found that the Nb atom in NbSi_n^-/0 prefers to occupy the high coordination sites to form more Nb-Si bonds. The most stable structures of NbSi_3-7^-/0 are all exohedral structures with the Nb atom face-capping the Si_n frameworks. At n = 8, both the anion and neutral adopt a boat-shaped structure and the openings of the boat-shaped structures remain unclosed in NbSi_9-10^-/0 clusters. The most stable structure of the NbSi₁₁^- anion is endohedral, while that of neutral NbSi₁₁ is exohedral. The global minima of both the NbSi₁₂^- anion and neutral NbSi₁₂ are D_6h symmetric hexagonal prisms with the Nb atom at the center. The perfect D_6h symmetric hexagonal prism of NbSi₁₂^- is electronically stable as it obeys the 18-electron rule and has a shell-closed electronic structure with a large HOMO-LUMO gap of 2.70 eV. The molecular orbital analysis of NbSi₁₂^- suggests that the delocalized Nb-Si₁₂ ligand interactions may contribute to the stability of the D_6h symmetric hexagonal prism. The AdNDP analysis shows that the delocalized 2c-2e Si-Si bonds and multicenter-2e NbSi_n bonds are important for the structural stability of the NbSi₁₂^- anion.