Atomic Contributions Research Articles

Benchmark Investigation of SCC-DFTB Against Standard DFT to Model Phononic Properties in Two-Dimensional MOFs for Thermoelectric Applications.

Despite the importance of modeling lattice thermal conductivity in predicting thermoelectric (TE) properties, computational data on heat transport, especially from first-principles, in 2D metal-organic frameworks (MOFs) remain limited due to the high computational cost. To address this, we provide a benchmark of the performance of semiempirical self-consistent-charge density functional tight-binding (SCC-DFTB) methods against density functional theory (DFT) for monolayer, serrated, AA-stacked and/or AB-stacked Zn3C6O6, Cd3C6O6, Zn-NH-MOF, and Ni3(HITP)2 MOFs. Harmonic lattice dynamics calculations, including partial atomic contributions to phonon dispersions, are evaluated with both SCC-DFTB and DFT, whereas anharmonic transport (i.e., thermal conductivity) is evaluated with SCC-DFTB only. Our findings further suggest that unlike the other stacking geometries modeled, serrated Zn3C6O6, serrated Zn-NH-MOF, and wavy serrated Ni3(HITP)2 represent stable geometries. While Zn3C6O6 and Zn-NH-MOF exhibit a higher power factor than Ni3(HITP)2 (as found in our previous work), Zn-NH-MOF shows lower thermal conductivity, resulting in the highest thermoelectric figure of merit (ZT) among the studied MOFs.

Intrinsic Chemical Drivers of Organic Aerosol Volatility: From Experimental Insights to Model Predictions

AbstractAccurately predicting the volatilities of molecules in aerosols is challenging but crucial for understanding the atmospheric effects of aerosols. We used negative and positive ion electrospray ionization Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) to identify differences in the molecular compositions of gas and particle phase samples from urban atmosphere. We aimed to identify intrinsic chemical parameters that determine and predict the organic aerosol volatility. We found higher average molecular weights, carbon mass percentages, and double bond equivalents (DBE) but lower average O/C ratios and oxygen mass percentages in the particle phase than the gas phase. We identified DBE, which display a significant negative correlation with volatility, as a key parameter. We proposed to improve the previous model for predicting organic aerosol volatility by incorporating DBE as a new variant; and the result showed that this subsequently improved the accuracy of the model, particularly for compounds with minimal or no heteroatoms (0–2) such as hydrocarbons (CH). The revised model offers insights into the contributions of DBE, carbon, nitrogen, oxygen, and sulfur atoms to the volatilities of diverse organic molecules in aerosols and could be applied to improve our understanding of the phase distributions of volatile organic compounds in the ambient air.

Experimental and molecular simulation study of CO2 adsorption in ZIF-8: Atomic heat contributions and mechanism

We successfully synthesised ZIF-8 using the solvothermal method at room temperature to study CO2 adsorption storage at 273 and 298 K up to 35 bar. Characterisation methods such as BET, SEM-EDS, XRD, and TGA were used to measure the physical and composition properties of ZIF-8. Grand canonical Monte Carlo (GCMC) simulation was conducted to compare with experimental data and get inside of the CO2 adsorption mechanism by calculating the isosteric heat and its fluid–fluid and solid–fluid contributions. The second was also split into fluid–solid atom contributions to understand in detail the interaction between CO2 and ZIF-8. The analyses revealed that there are three main stages during the CO2 adsorption gas–solid atom contributions, developing, pore-filling and densification. During the developing and pore-filling stages the largest fluid–solid atom contribution to the isosteric heat is CO2-C2 interactions, indicating that the CO2 is adsorbed close to the hexagonal windows of the ZIF-8 structure, while during the densification stage the largest contribution is CO2-N interactions. Where C2 and N refers to C-atom and N-atom, respectively in NCH group of the solid framework. This is because CO2 changes its orientation to be able to accommodate more molecules in the pore cavity. This work provides a better understanding of the adsorption mechanism of CO2 on ZIF-8 and shows how molecular simulation can be used to improve the understanding gas adsorption storage on metal–organic frameworks.

Mechanism and chemoselectivity of nitrile hydrosilylation catalyzed by [E-Rh] (E=Al, Ga, In) heterobimetallic catalysts: A theoretical perspective

Transition metals catalyzed hydrosilylation reaction is of significant values in organic synthesis. Herein the detailed mechanisms of the phenylacetonitrile hydrosilylation catalyzed by bimetallic [E-Rh] (E=Al, Ga, In) catalysts, as well as the RhCl(PPh3)3 monometallic catalyst, were investigated by DFT calculations. The electronic structure analysis indicates that the different atomic contributions of the Rh atom in E-Rh bond result in the polarity variations of the metal-metal bonds and different catalytic activities. The whole catalyzed cycle involves five processes: the formation of rhodium hydride complex, activation of H2SiMe2, insertion of phenylacetonitrile, reductive elimination, and isomerization. The reaction activities of [E-Rh] (E=Al, Ga, In) decrease successively, which is in agreement with the atomic contributions of Rh in three catalysts. DI analysis provides the evidence that the catalytic activity is controlled by the distortion energy of rate-determining state. QTAIM analysis shows the transformation of the Cl atom between two metal atoms, providing a clear description for structural changes in catalytic cycle.

A Discovery of Pressure-Induced New Semiconductor Electronic Phase Transitions by DFT Calculations: Introducing a Glimpse of a Novel Semiconductor Family.

This study introduces a discovery of pressure-induced new semiconductor electronic phase transitions. A novel semiconductor family that exhibits pressure-induced nonmonotonic changes in band gaps was found and meets the definition of phase transitions, challenging the traditional understanding of linear and monotonic band gap modification through pressurization. Our findings suggest a complex interplay of atomic spacing and electron orbital contributions under varying pressure conditions, resulting in the variation of band gaps. This behavior, which includes three distinct steps: first, narrowing, second, broadening, and third, narrowing again and ultimately metalizing; some compounds could bypass step 1, has potential applications in piezoelectric and semiconductor technologies. We propose two new semiconductor electronic phase transitions (SEPT) associated with specific inflection points in the pressure-dependent band gap curve. Our results open avenues for further research into the electronic properties of crystals under high pressure, with the ultimate goal of uncovering the more profound physical principles governing these phenomena.

Controllable orbital angular momentum monopoles in chiral topological semimetals

AbstractThe emerging field of orbitronics aims to generate and control orbital angular momentum for information processing. Chiral crystals are promising orbitronic materials because they have been predicted to host monopole-like orbital textures, where the orbital angular momentum aligns isotropically with the electron’s crystal momentum. However, such monopoles have not yet been directly observed in chiral crystals. Here, we use circular dichroism in angle-resolved photoelectron spectroscopy to image orbital angular momentum monopoles in the chiral topological semimetals PtGa and PdGa. The spectra show a robust polar texture that rotates around the monopole as a function of photon energy. This is a direct consequence of the underlying magnetic orbital texture and can be understood from the interference of local atomic contributions. Moreover, we also demonstrate that the polarity of the monopoles can be controlled through the structural handedness of the host crystal by imaging orbital angular moment monopoles and antimonopoles in the two enantiomers of PdGa, respectively. Our results highlight the potential of chiral crystals for orbitronic device applications, and our methodology could enable the discovery of even more complicated nodal orbital angular momentum textures that could be exploited for orbitronics.

First principles calculations of double perovskite RbX2Y3O10 (X = Ca, Ba: Y[dbnd]Cd, Ta) materials for photocatalytic applications

Production of oxygen and hydrogen energy through suited photocatalysts by water splitting is the main issue in the modern age. In this regard, the double perovskite Dion-Jacobson materials RbX2Y3O10 (X = Ca, Ba: YCd, Ta) for photocatalytic activity are investigated by using the CASTEP package. The plane-wave (PW) pseudo-potential in the context of the generalized gradient approximation (GGA)-Perdew Burke Ernzerhof (PBE) and local density approximation (LDA) exchange-correlation functional technique is used to investigate the compounds. According to the results, compounds have a tetragonal (a = b≠c) structure with space group 123 (p4/mmm). Compounds Mullikan bond populations were estimated in order to comprehend the bonding characteristics that found a mixed ionic and covalent bonding. According to electronic characteristics, RbBa2Ta3O10, RbBa2Cd3O10, and RbCa2Cd3O10 have semiconductor behavior with indirect bandgap of 2.11 eV, 2.27 eV, and 1.51 eV, respectively, and respond under visible region light. DOS and PDOS are studied to inspect the distinct atom's contribution to electronic band structure. The compounds are mechanically brittle (1.55, 1.39), ductile (1.97), and stable in their natural form, according to elastic constant values. The optical characteristics simulation indicates that compounds have the potential to decompose or oxidize organic contaminants. According to the results, these compounds are suitable for the water-splitting photocatalytic process to produce oxygen and hydrogen.

Contributions of Edge and Internal Atoms to the Friction of Two-Dimensional Heterojunctions.

The weak interlayer interaction and strong intralayer bonding in Van der Waals (vdW) layered materials give rise to ultralow friction at incommensurate contact interfaces, a phenomenon known as structural superlubricity. This phenomenon is complicated by the interplay between atomic degrees of freedom, twist angle, and normal force. In this Letter, we exploit naturally occurring cracks in vdW crystals and microfabrication techniques to qualitatively separate the contributions of edge, complete moiré tile, and incomplete moiré rim regions. It is observed that friction from the incomplete moiré rim region, scaling linearly with the rim area, plays a dominant role in determining the twist angle dependence of friction. Interestingly, despite lower friction contributions from complete moirés, friction from a complete moiré tile is independent of moiré size; consequently, friction from the moiré tile scales linearly with the total number of moirés. By integrating the contributions from edge, moiré tile, and incomplete moiré rim, a friction law for vdW heterojunctions is proposed. Finally, friction changes from positively to negatively correlating with normal force, contingent on the suppression of moiré ridge and the dissipation from edge atoms.

Simulation of ion beam sputtering with OKSANA and SRIM: A comparative study

The energy distributions and average energies of sputtered particles are calculated using simulation codes OKSANA and SRIM-2013. Most simulations refer to an amorphous Ni target bombarded by normally incident Ar ions of keV energies. Sputtering of Si, Ti, V and Nb targets is also considered. It is shown that SRIM can strongly overestimate the contribution of fast ejected atoms, especially for targets irradiated with lighter ions. The effect is amplified by using the surface binding energies found to fit the measured sputter yields. It is concluded that the enhanced ejection of fast particles is associated with sputtering due to backscattered ions. The role of the first collision of an incident ion with a target atom is particularly noted. A comparison of the OKSANA calculated results with the data of other codes (TRIM.SP, ACAT) and experimental data showed their reasonable agreement.

EXPLORING THE STRUCTURAL AND ELECTRONIC CHARACTERISTICS OF AMORPHOUS Ge – Te - In MATERIAL THROUGH AB INITIO METHODS

This study employs density functional theory (DFT) and molecular dynamics to meticulously investigate the structural and electronic properties of ternary chalcogenide compounds, specifically (GeTe4 ) 1-x Inx, and (GeTe5 )1-x Inx across a range of compositions ( x = 0, 5, 10, 15, 20 at %). Utilizing the local density approximation within the framework of first-principles calculations, we comprehensively analyze the pair correlation function, static structural factor, electronic density of states, and electronic band gap energy. Our results reveal a notable decrease in the energy band gap of Germanium-Tellurium with the incorporation of Indium atoms. The structural changes observed in the Ge-Te matrix with Indium doping, as evidenced by the changes in the pair correlation function and static structure factor, are consistent with and supportive of the observed decrease in the band gap energy. This phenomenon is primarilyattributed to the significant contribution of Indium atoms to the conduction band edge, offering new insights into the material’s electronic behaviour.

Long-Chain Molecular Crystals Antimony(III) Alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12): Synthesis, Crystal and Electronic Structures, and Supramolecular Self-Assembly via Secondary Interactions.

Currently, there is not much success in solving the molecular and crystal structures of long-chain metal alkanethiolate complexes [M(SCnH2n+1)m] at the atomic level. Taking Sb(SC16H33)3 (1) as an example, we herein disclose the structural characteristics of long-chain trivalent antimony(III) alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12) by single-crystal X-ray crystallography. Specifically, the Sb atom is three-coordinated by alkanethiolate ligands and a slightly distorted triangular pyramid SbS3 core is formed owing to the unique intramolecular stereochemistry of three alkyl chains, namely, two of them almost parallel aligning and the third chain extending alone around the SbS3 core. We further determine the conformation, spatial orientation and packing density of alkyl chains in 1 along with a comparison to those in other long-chain crystalline systems, and reveal the roles of intermolecular van der Waals and Sb···S secondary interactions in molecular self-assembly, which enables 1 to be a layer-structured molecular crystal with a monoclinic P21/c unit cell. The band structures and the atomic orbital contributions to the valence band maximum and conduction band minimum for 1 have also been evaluated by DFT calculations and rationally correlated with its optical absorption property. This study will help understand and discover new structures and structure-property relations of long-chain chemical systems.

Quantifying the contribution of lanthanum single atoms in photocatalytic Fenton-like processes with a rigorous benchmarking protocol

Quantifying the contribution of lanthanum single atoms in photocatalytic Fenton-like processes with a rigorous benchmarking protocol

The physical properties of crystalline iron-rich silicides

The formation enthalpy, electronic structure, lattice dynamics and elasticity of several complex ordered iron-rich silicides (Fe11Si5, Fe13Si3, Fe17Si12 and Fe24Si5) are calculated from the first-principles calculations. It is found that the Debye temperature ΘD of the system decreases with the increase of the ratio of the number of iron atoms to the number of silicon atoms in the same structure. The softening of low-energy acoustic phonons is more obvious with the increase of iron atoms. The elastic constants C11 and C44, Young's modulus E and shear modulus G of the system decrease with the increase of iron atoms. An anomalous phenomenon occurs in the high frequency region of Fe24Si5. The contribution of Fe1 atoms with smaller magnetic moment to the phonon density of states is much larger than that of the Si and other Fe atoms. This indicates that the local metal bond strength between Fe1-Fe1 atoms is stronger.

Proposing novel predictive group and atomic contribution models for hydrogen sulfide absorption by Deep Eutectic Solvents

Hydrogen sulfide (H2S) is one of the most dangerous impurities of natural gas which cause human and environmental issues. Thus, the main process of gas sweetening plants is H2S removal from natural gas. Amine solutions are the commonly used solvents for gas-sweetening processes in petroleum industries. However, amin solutions are not safe and cause many environmental issues especially in the post-process treatment of used amine. Thus, the issue of proposing green sustainable solvents for gas sweetening is vital for petroleum industries. Deep Eutectic Solvents (DESs) are the most recently introduced green solvents which have shown good capability for H2S absorption. Thus, DESs are one of the most possible candidates for green solvents to replace amine solutions. Experimental studies to choose suitable solvents is a tough challenge because working with H2S is very dangerous and requires expensive facilities. Therefore, an accurate and global thermodynamic model is necessary to predict the solubilities of H2S in DESs without the requirement of experimental data. This study for the first time in open literature, proposes two accurate and global thermodynamic models of group contribution (GC) and atomic contribution (AC) for predicting the H2S solubilities in various nature DESs. The largest and most updated data bank for H2S solubility in DESs was developed from open literature, including 415 solubility data of 37 different nature DESs. The proposed GC and AC models were developed according to the gathered data bank and their results were analyzed by statistical parameters. Both GC and AC models show normal behavior and promising results concerning experimental data by the calculated AARD% of 9.64, and 12.86, respectively.

An Efficient Sparse Recovery STAP Algorithm for Airborne Bistatic Radars Based on Atomic Selection under the Bayesian Framework

The traditional sparse recovery (SR) space-time adaptive processing (STAP) algorithms are greatly affected by grid mismatch, leading to poor performance in airborne bistatic radar clutter suppression. In order to address this issue, this paper proposes an SR STAP algorithm for airborne bistatic radars based on atomic selection under the Bayesian framework. This method adopts the idea of atomic selection for the process of Bayesian inference, continuously evaluating the contribution of atoms to the likelihood function to add or remove atoms, and then using the selected atoms to estimate the clutter support subspace and perform sparse recovery in the clutter support subspace. Due to the inherent sparsity of clutter signals, performing sparse recovery in the clutter support subspace avoids using a massive number of atoms from an overcomplete space-time dictionary, thereby greatly improving computational efficiency. In airborne bistatic radar scenarios where significant grid mismatch exists, this method can mitigate the performance degradation caused by grid mismatch by encrypting grid points. Since the sparse recovery is performed in the clutter support subspace, encrypting grid points does not lead to excessive computational burden. Additionally, this method integrates out the noise term under a new hierarchical Bayesian model, preventing the adverse effects caused by inaccurate noise power estimation during iterations in the traditional SR STAP algorithms, further enhancing its performance. Our simulation results demonstrate the high efficiency and superior clutter suppression performance and target detection performance of this method.

Computational study to investigate effectiveness of titanium substitution in CaFeH3 perovskite-type hydride: An approach towards advanced hydrogen storage system

In recent years, there has been increased interest in hydrogen storage due to the numerous advantages hydrogen offers as an energy source. This study explores the structural, hydrogen storage, electronic, elastic, mechanical, and optical properties of Ca1-xTixFeH3 through DFT. After Ti substitution in the host material, structure phase transformation occurs: cubic → pseudo-cubic → cubic. Study compounds are thermodynamically stable and experimentally synthesizable according to the calculated negative formation energies. Gravimetric hydrogen storage capacities for different concentrations of Ti (x = 0, 0.11, 0.33, 0.55, 1) were calculated as 2.963, 2.938, 2.843, and 2.753 wt%, respectively. The investigation focuses on understanding the material's BS, Fermi level, and DOS, elucidating its metallic characteristics, and non-zero DOS at the Fermi level contributing to electrical and thermal conductivity. Elemental partial density of states reveals hybridization effects with Ti doping, affecting the valence band's atomic contributions. Using cubic symmetry, C11, C12, and C14 elastic constants were used to describe mechanical characteristics, and the Born criteria were met. Thus, mechanical stability was demonstrated for these compounds. Optical analyses exhibit changes concerning Ti concentrations and energy levels, including absorption spectra, conductivity, reflectivity, dielectric function, refractive index, energy loss function, and extinction coefficient. These findings shed light on the material's response to incident radiation and potential applications in hydrogen storage and optoelectronic devices.

A polarizable valence electron density based force field for high-energy interactions between atoms and molecules.

High-accuracy molecular force field models suited for hot gases and plasmas are not as abundant as those geared toward ambient pressure and temperature conditions. Here, we present an improved version of our previous electron-density based force field model that can now account for polarization effects by adjusting the atomic valence electron contributions to match abinitio calculated Mulliken partial charges. Using a slightly modified version of the Hohenberg-Kohn theorem, we also include an improved theoretical formulation of our model when applied to systems with degenerate ground states. We present two variants of our polarizable model, fitted from abinitio reference data calculated at CCSD(T)/cc-pVTZ and CCSD(T)/CEP-31G levels of theory, that both accurately model water dimer interaction energies. Further improvements include the additional interaction components with fictitious non-spherically symmetric, yet atom-centered, electron densities and fitting the exchange and correlation coefficients against analytical expressions. The latter removes all unphysical oscillations that are observed in the previous non-polarizable variant of our force field.

Carbon dioxide interaction with a series of ionic liquids consisting of fluorophenyltrifluoroborate anions studied by in situ ATR-FTIR spectroscopy

Fluorinated ionic liquids have new and unique properties by combining the properties of highly fluorinated compounds and ionic liquids. In this work, the interaction of CO2 with ionic liquids containing fluorophenyltrifluoroborate anions ([BMIM][C6H5BF3], [BMIM][4-F-C6H4BF3], [BMIM][C6F5BF3], [BMIM][4-BuO-C6F4BF3]) has been studied for the first time using high-pressure in situ ATR-FTIR spectroscopy. Analysis of the IR spectra of ionic liquids recorded under CO2 pressure showed disaggregation of alkyl groups and a slight decrease in cation–anion interaction, based on the appearance of a blue shift of absorption bands characteristic of stretching vibrations of CH bonds in alkyl groups, aromatic and imidazolium rings. It was found that fluorination of the phenyl group and introduction of a butoxy group significantly increased the solubility of CO2. The enthalpy and entropy of CO2 dissolution also increase with the increase of fluorine atoms in the anion. Theoretical calculations using the DFT method also showed an increase in the energy of interaction of CO2 with ionic liquids with an increase in the number of fluorine atoms. The use of an independent gradient model based on Hirshfeld partition (IGMH) analysis allowed the patterns of splitting of the CO2 bending ν2 mode to be explained. It was found that in this series of ionic liquids, the degree of the splitting of the CO2 bending mode depends on the contributions of the CO2 atoms to the interaction with the ionic liquid, rather than on the interaction energy.

Achieving enhanced thermal conductivity and mechanical properties in Mg-Zn-Gd-Zr alloys via regulation microstructure characteristics

It is well known that the microstructure of metallic materials determines the mechanical properties. However, the effect of microstructure on thermal conductivity lacks an accurate quantitative description of this relationship. In this work, the mechanism of variation in mechanical and thermal conductivities with microstructure was revealed by the characterization of cast, heat-treated, and extruded Mg-xZn-yGd-0.6Zr (wt%) alloys: ZV66, ZV62, and ZV26. The contributions of solution atoms, second phases, grain size, and dislocations to the yield strength and thermal conductivity were quantitatively calculated, and their effects on the plasticity and work-hardening behavior were qualitatively analyzed. The results show that hot extrusion promotes the precipitation of nanoprecipitates, such as MgZn2, Mg4Zn7, and Mg5Gd, resulting in the reduction of Zn and Gd solute atoms and the introduction of high-density dislocations and grain boundaries. The extruded ZV66 alloy exhibits excellent mechanical properties and thermal conductivity (a tensile yield strength of 232 MPa, an elongation of 22 %, and a thermal conductivity of 127.6 W/(m·k)); these values are better than those reported for similar products. The achievement of high strength and thermal conductivity is attributed to the precipitation of solute atoms to improve thermal conductivity in addition to grain boundary strengthening and work-hardening strengthening to improve strength. These findings provide new insights into achieving excellent strength–thermal conductivity property amalgamations in magnesium alloys by tailoring their microstructure.

First-principles study of the structural, mechanical, electronic, optical, and elastic properties of non-toxic XGeBr3 (X=K, Rb, and Cs) perovskite for optoelectronic and radiation sensing applications

In this study, a comprehensive analysis of the structural, electronic, optical, and elastic properties of cubic perovskite structure XGeBr3(X=K,Rb,andCs) was carried out using GGA-PBE functional based density functional theory in CASTEP code. The simulated values of the lattice parameter were increased with the changing of X from K to Cs (a = 5.51 Å, 5.54 Å, and 5.59 Å respectively). All the compounds possessed direct band gaps and acquired values for the structures KGeBr3, RbGeBr3 and CsGeBr3 were 0.525 eV, 0.599 eV, and 0.708 eV, respectively. Furthermore, the atomic orbital's contribution to the formation of band structure was clarified thoroughly. The thermodynamic, as well as the mechanical stability, has been accomplished with the assurance of negative formation energy and Born-Huang approximation. In addition, a larger shearing modulus attained by CsGeBr3 manifests its strength. Moreover, all structures bear the proof of having ductility and existing central force inside the structures. Finally, the calculated anisotropic index notifies that all structures exhibit anisotropy with the trend of CsGeBr3 < RbGeBr3 < KGeBr3. This is also authenticated through the 3D anisotropy contour plot generated by utilizing ELATE software, which is for the first time in regard to the comparative scenario among them. With the investigation of the optical characteristics of the compounds XGeBr3, intriguing features such as broad absorption spectrum, high dielectric function and refractive index at zero photon's energy, and high conductivity have been affirmed accompanying the marginal value of loss function as well as reflectivity that elevates the probability of being employed in optoelectronic applications along with different absorber layers of tandem solar cells. In addition, these compounds could be used as radiation detectors since they have broad absorption at extreme ultraviolet rays.