Ab Initio Analysis Research Articles

Role of Anharmonic Effects on the Phase Stability of VNbMoTaW High-Entropy Alloy from Ab Initio Analysis

Role of Anharmonic Effects on the Phase Stability of VNbMoTaW High-Entropy Alloy from Ab Initio Analysis

Novel superhard orthorhombic O12 carbon: a first principle study

Abstract In this study, a new orthorhombic carbon structure with Ama2 symmetry, designated as O12 carbon, has been predicted on basis of the first-principles method. The thermal stability and dynamic stability of O12 carbon were evaluated and confirmed by combining ab initio molecular dynamics and phonon spectra analyses. Meanwhile, the mechanical properties of O12 carbon, compared with other superhard carbon allostrope like diamond, M-carbon, Bct-c4 and Cco-C8, have also been systematically investigated. With a bulk modulus of 351 GPa, a shear modulus of 333 GPa, and a Vickers hardness of 53 GPa, O12 carbon is identified as a superhard material of significantly technological and industrial applications. The existence of elastic anisotropy in O12 carbon has also been confirmed. The electronic band structure calculations have revealed that O12 carbon exhibits a semiconductor characteristic with a direct band gap of 2.5 eV, making it promising candidate in electronic applications. Additionally, the XRD spectra of O12 carbon were obtained to offer further insights for potential experimental observations. Our findings enrich the family of carbon structure and are expected to stimulate additional experimental interest.

Prediction of Chemistry of Cocrystallization and its Realistic Impact on the Enhancement of Solubility and Dissolution of Telmisartan: Molecular mechanics, ab initio and Descriptor Analysis

Prediction of Chemistry of Cocrystallization and its Realistic Impact on the Enhancement of Solubility and Dissolution of Telmisartan: Molecular mechanics, ab initio and Descriptor Analysis

Experimental and ab-initio analysis of structural, electronic and optical properties of ZMCO thin films elaborated by sol-gel method for optoelectronic application

Experimental and ab-initio analysis of structural, electronic and optical properties of ZMCO thin films elaborated by sol-gel method for optoelectronic application

Enhanced Superconductivity of Hydrogenated β12 Borophene.

Borophene stands out among elemental two-dimensional materials due to its extraordinary physical properties, including structural polymorphism, strong anisotropy, metallicity, and the potential for phonon-mediated superconductivity. However, confirming superconductivity in borophene experimentally has been evasive to date, mainly due to the detrimental effects of metallic substrates and its susceptibility to oxidation. In this study, we present an ab initio analysis of superconductivity in the experimentally synthesized hydrogenated β12 borophene, which has been proven to be less prone to oxidation. Our findings demonstrate that hydrogenation significantly enhances both the stability and superconducting properties of β12 borophene. Furthermore, we reveal that tensile strain and hole doping, achievable through various experimental methods, significantly enhance the critical temperature, reaching up to 29 K. These findings not only promote further fundamental research on superconducting borophene and its heterostructures, but also position hydrogenated borophene as a versatile platform for low-dimensional superconducting electronics.

Boosting CO oxidation performance via reaction-induced single-atom active site: DFT and microkinetic investigation of a unified CO oxidation mechanism on Gd-doped ceria supported copper catalysts

Single-atom (SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities. However, SA catalysts are often plagued by the aggregation and deactivation of SA sites under reaction conditions. This study focuses on CO oxidation over Gd-doped ceria supported Cu catalysts and aims to provide a new strategy to stabilize the SA site, in which a Cu SA site is “prestored” in a relatively stable Cu cluster and can be dynamically activated under reaction conditions. Three typical Cu10/CeO2 catalyst models were built with different Gd-doping contents, which are pristine Cu10/CeO2, Cu10/Gd0.125Ce0.875O2, and Cu10/Gd0.25Ce0.75O2, respectively. We performed density functional theory (DFT) calculations on the Cu10/Gd-CeO2 system to investigate the adsorption of CO and O2 molecules, the formation of surface oxygen vacancy (OV) and dynamic Cu SA site, and potential energy surfaces of CO oxidation process. Ab initio thermodynamic analysis suggests that the saturation adsorption of CO on Cu10 and high Gd-doping in CeO2 lead to a spontaneously formed single Cu−CO site and an OV defect on ceria surface. The CO oxidation process is identified as a two-paths-coupled catalytic cycle, in which Path I is activated by the terminal O atom of adsorbed O2 at surface OV site while Path II initiates with the lattice O atom of CeO2 surface. The microkinetic modeling demonstrates that the dominant pathway is Path I for the undoped and low-doping cases, and Path II for the high-doping case which exhibits a novel mechanism for CO oxidation and the highest reaction activity due to the participation of the dynamic SA site.

Ab initio analysis of structural, electronic, magnetic, thermodynamic, and elastic properties of Half Heusler alloys ZMnAs (Z = Be, Mg) for spintronics applications

In this study, the structural, electronic, magnetic, thermodynamic, and elastic attributes of ZMnAs (Z = Be, Mg) have been investigated. These Half-Heusler alloys exhibit stability in the ferromagnetic state (FM), as demonstrated by optimization-related energy release. The half-metallicity (HM) of these compounds is examined through the band structures and density of states (DOS). In addition, the crystal field and exchange energies are reported to confirm the control of electron spin. Additionally, the double exchange process and exchange constants were premeditated. In this case, ferromagnetism (FM) is caused by the quantum exchange of electrons, as evidenced by the negative pd exchange energy and the exchange constants, rather than being a result of clustering effects. The quasi-harmonic Debye model, included within the Gibbs code, was utilized to calculate the thermodynamic properties. These two compounds are mechanically stable and show ductile nature confirmed by the value of Poisson's ratio (v), Pugh's ratio (B/G), and Cauchy pressure (CP), which demonstrates the ability to withstand substantial plastic deformation before fracturing. Based on our calculations, the half-metallic (HM) nature, thermodynamic, ferromagnetic, ductile, and high inherent magnetic moment have been evaluated. These alloys are crucial in the advancement of spintronics and renewable energy systems.

(Invited) Material Engineering for the GAA and Post-GAA Transistors and Interconnects

Feature scaling in advanced CMOS technology has been slowing down starting at 10 nm node and is expected to stop completely in the next few years. Nevertheless, transistor density scaling is continuing at a Moore’s law pace, driven by DTCO and 3D IC.Transistor dimensions and minimum metal pitch are expected to be massaged down only by 10% to 20% during the next decade. However, both the transistor and the interconnect will continue to evolve and improve both in performance and in variability.Currently, the industry is transitioning from FinFET technology to GAA (Gate All-Around) technology. The next transition, from GAA to the NMOS and PMOS GAA transistors stacked on top of each other (often referred to as CFET (Complementary Field Effect Transistor)) is expected in 8 to 10 years from now.The main methodology for GAA and CFET transistor engineering comes down to bandstructure engineering, where material composition, shape and thickness of different layers, and mechanical stress are engineered to tailor a bandstructure of the channel that maximizes on-state driving strength and minimizes off-state leakage and variability. The key methodology for bandstructure engineering is ab-initio analysis of transistor components and then transfer of the obtained bandstructure to transistor scale analysis to characterize its behavior.For the interconnect engineering, the tight metal pitches and increasingly tall and narrow vias dictate transition from copper to alternative metals, with a preference for the metals that can be etched and selectively grown. The key methodology for interconnect engineering is ab-initio analysis of electron scattering at the interfaces and grain boundaries. The scattering is then converted into interconnect resistance that defines speed and power consumption of the advanced CMOS circuits.This work introduces the concepts of transistor band structure engineering and interconnect scattering engineering and provides illustrations of these methodologies applied to GAA and post-GAA technologies.

Reproducibility of the Optical Absorption Edge in Amorphous GeS2

Herein, poor reproducibility of optical absorption edges in GeS2 glasses and films is seen. Reported spectral positions of the absorption edge in melt‐quenched glasses spread over ≈0.2 eV at ħω ≈ 3 eV. In deposited films, the edge red‐shifts to ħω ≈ 2.5 eV showing wider variations of ≈1 eV. This work considers plausible reasons of such low, spectral reproducibility, with the aid of ab initio molecular orbital analyses of Ge–S clusters and known insights on optical gaps, electron‐spin‐resonance signals, and structural data. The variation in the glass is likely to be governed by several factors including compositional fluctuation, edge/corner‐shared configurations, wrong bonds, and intimate valence‐alternation pairs. The conspicuous red‐shift in the films seems to be affected also by neutral dangling bonds.

Unraveling the Mechanistic Origin of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst.

NH3 emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM2.5 formation. Ammonia selective catalytic oxidation to N2 (NH3-SCO) is a promising route for NH3 emission control, but the mechanistic origin of achieving high N2 selectivity remains elusive. Here we constructed a highly N2-selective CuO/TiO2 catalyst and proposed a CuOx dimer active site based on the observation of a quadratic dependence of NH3-SCO reaction rate on CuOx loading, ac-STEM, and ab initio thermodynamic analysis. Combining this with the identification of a critical N2H4 intermediate by in situ DRIFTS characterization, a comprehensive N2H4-mediated reaction pathway was proposed by DFT calculations. The high N2 selectivity originated from the preference for NH2 coupling to generate N2H4 over NH2 dehydrogenation on the CuOx dimer active site. This work could pave the way for the rational design of efficient NH3-SCO catalysts.

Picturing the Gap Between the Performance and US-DOE's Hydrogen Storage Target: A Data-Driven Model for MgH2 Dehydrogenation.

Developing solid-state hydrogen storage materials requires a comprehensive understanding of the dehydrogenation chemistry of a solid-state hydride. Transition state search and kinetics calculations are essential to understanding and designing high-performance solid-state hydrogen storage materials by filling in the knowledge gap that current experimentscannot measure. However, the ab initio analysis of these processes is expensive and time-consuming. Searching for descriptors to accurately predict the energy barrier is urgently needed, to accelerate the prediction of hydrogen storage material properties and identify the opportunities and challenges. Herein, we develop a data-driven model to describe and predict the dehydrogenation barriers of a typical solid-state hydrogen storage material, MgH2, based on the combination of the crystal Hamilton population orbital of Mg-H bond and the distance between atomic hydrogen.All the parameters in this model can be directly calculated with significantly less computational cost than conventional transition state search, so that the dehydrogenation performance of hydrogen storage materials can be predicted efficiently. Finally, we found that this model leads to excellent agreement with typical experimental measurements reported to date and provides clear design guidelines on how to propel the performance of MgH2 closer to the target set by the United States Department of Energy (US-DOE).

Picturing the Gap Between the Performance and US‐DOE's Hydrogen Storage Target: A Data‐Driven Model for MgH2 Dehydrogenation

AbstractDeveloping solid‐state hydrogen storage materials is as pressing as ever, which requires a comprehensive understanding of the dehydrogenation chemistry of a solid‐state hydride. Transition state search and kinetics calculations are essential to understanding and designing high‐performance solid‐state hydrogen storage materials by filling in the knowledge gap that current experimental techniques cannot measure. However, the ab initio analysis of these processes is computationally expensive and time‐consuming. Searching for descriptors to accurately predict the energy barrier is urgently needed, to accelerate the prediction of hydrogen storage material properties and identify the opportunities and challenges in this field. Herein, we develop a data‐driven model to describe and predict the dehydrogenation barriers of a typical solid‐state hydrogen storage material, magnesium hydride (MgH2), based on the combination of the crystal Hamilton population orbital of Mg−H bond and the distance between atomic hydrogen. By deriving the distance energy ratio, this model elucidates the key chemistry of the reaction kinetics. All the parameters in this model can be directly calculated with significantly less computational cost than conventional transition state search, so that the dehydrogenation performance of hydrogen storage materials can be predicted efficiently. Finally, we found that this model leads to excellent agreement with typical experimental measurements reported to date and provides clear design guidelines on how to propel the performance of MgH2 closer to the target set by the United States Department of Energy (US‐DOE).

High-Resolution Diatomic Spectroscopy near the Dissociation Threshold

Current progress in and prospects for high-resolution molecular laser spectroscopy used for quantum-mechanical modeling of the energy and radiation properties of the rovibronic states of diatomic molecules near the dissociation threshold are discussed at the experimental (spectroscopic) level of accuracy, which is impossible without taking into account all types of intramolecular interactions. The weakly bound, quasibound, and continuum rovibronic states localized near the dissociation threshold actively participate in the formation of stable molecules during spontaneous or laser-stimulated association of colliding atoms, which leads to cooling of the initial reaction medium. Laser-induced fluorescence (LIF) combined with high-resolution Fourier transform spectroscopy is a unique experimental technique, which allows the study of all the three (bound, quasibound, and continuum) parts of the molecular spectrum simultaneously. LIF experiments combined with precision ab initio electronic structure calculations and global nonadiabatic analysis of quasidegenerate rovibronic states converging to the same dissociation limit make it possible to study the structural and dynamic properties of isolated molecules over a very wide range of their electronic-vibrational-rotational excitation.

A striking exploration of defect engineering in HfS2, HfSe2, and janus HfSSe through ab initio analysis for HER catalysis application

The present study emphasizes the enhancement in catalytic activity due to the formation of vacancies using dispersion corrected density functional theory. We observed that without vacancy formation, in general the edge site is an active site for hydrogen adsorption, while the lowest Gibbs free energy (ΔGH) is found to be for Janus HfSSe at the S-edge site. Furthermore, interestingly, due to the hindrance of the edge site, it facilitates only the Volmer-Heyrovsky reaction rather than the Volmer-Tafel. Among the mono vacancies, the Hafnium mono vacancy shows the lowest adsorption energy.We observed a competition between the evolution of H2S and H2 gas in the case of HfS2-VHf, whereas in the case of defected Janus and HfSe2, due to the presence of Se layers, we observed no competitiveness with H2S or H2Se gas with hydrogen gas. These defected materials exhibit lower reactional Gibbs free energy than a pristine monolayer due to its metallic nature. We observed that Hafnium vacancy enhances the HER activity, and pave the way for dominating Volmer-Heyrovsky reaction.

Ab initio analysis of structural, optoelectronic, thermoelectric, and elastic characteristics of K2MBiBr6 (M = Na, Ag, and Cu) for green energy

Ab initio analysis of structural, optoelectronic, thermoelectric, and elastic characteristics of K2MBiBr6 (M = Na, Ag, and Cu) for green energy

A DFT study on the mechanical, optical, and electronic properties of (Ga,Al)N counterparts of T-Graphene

This study employs density functional theory calculations to investigate the unique properties of aluminum nitride (AlN) and gallium nitride (GaN) analogs of T-Graphene, denoted as TAlN and TGaN. We explore their mechanical, electronic, and optical properties. Results revealed that the lattice topology of these materials introduces isotropy in optical and mechanical properties. Their Young modulus varies between 12–112 GPa. Phonon dispersion and ab initio molecular dynamics analysis suggest their dynamic and thermal stabilities. The optical analysis demonstrates high absorption coefficients and reflectivity peaks in the UV region for these materials.

Convergent abinitio analysis of the multi-channel HOBr + H reaction.

High-level potential energy surfaces for three reactions of hypobromous acid with atomic hydrogen were computed at the CCSDTQ/CBS//CCSDT(Q)/complete basis set level of theory. Focal point analysis was utilized to extrapolate energies and gradients for energetics and optimizations, respectively. The H attack at Br and subsequent Br-O cleavage were found to proceed barrierlessly. The slightly submerged transition state lies -0.2kcal mol-1 lower in energy than the reactants and produces OH and HBr. The two other studied reaction paths are the radical substitution to produce H2O and Br with a 4.0kcal mol-1 barrier and the abstraction at hydrogen to produce BrO and H2 with an 11.2kcal mol-1 barrier. The final product energies lie -37.2, -67.9, and -7.3kcal mol-1 lower in energy than reactants, HOBr + H, for the sets of products OH + HBr, H2O + Br, and H2 + BrO, respectively. Additive corrections computed for the final energetics, particularly the zero-point vibrational energies and spin-orbit corrections, significantly impacted the final stationary point energies, with corrections up to 6.2kcal mol-1.

Compression Eliminates Charge Traps by Stabilizing Perovskite Grain Boundary Structures: An Ab Initio Analysis with Machine Learning Force Field.

Grain boundaries (GBs) play an important role in determining the optoelectronic properties of perovskites, requiring an atomistic understanding of the underlying mechanisms. Strain engineering has recently been employed in perovskite solar cells, providing a novel perspective on the role of perovskite GBs. Here, we theoretically investigate the impact of axial strain on the geometric and electronic properties of a common CsPbBr3 GB. We develop a machine learning force field and perform ab initio calculations to analyze the behavior of GB models with different axial strains on a nanosecond time scale. Our results demonstrate that compressing the GB efficiently suppresses structural fluctuations and eliminates trap states originating from large-scale distortions. The GB becomes more amorphous under compressive strain, which makes the relationship between the electronic structure and axial strain nonmonotonic. These results can help clarify the conflicts in perovskite GB experiments.

Quantum-Chemistry Study of the Hydrolysis Reaction Profile in Borate Networks: A Benchmark.

This investigation involved an ab initio and Density Functional Theory (DFT) analysis of the hydrolysis mechanism and energetics in a borate network. The focus was on understanding how water molecules interact with and disrupt the borate network, an area where the experimental data are scarce and unreliable. The modeled system consisted of two boron atoms, bridging oxygen atoms, and varying numbers of water molecules. This setup allows for an exploration of hydrolysis under different environmental conditions, including the presence of OH- or H+ ions to simulate basic or acidic environments, respectively. Our investigation utilized both ab initio calculations at the MP2 and CCSD(T) levels and DFT with a range of exchange-correlation functionals. The findings indicate that the borate network is significantly more susceptible to hydrolysis in a basic environment, with respect to an acidic or to a neutral pH setting. The inclusion of explicit water molecules in the calculations can significantly affect the results, depending on the nature of the transition state. In fact, some transition states exhibited closed-ring configurations involving water and the boron-oxygen-boron network; in these cases, there were indeed more water molecules corresponding to lower energy barriers for the reaction, suggesting a crucial role of water in stabilizing the transition states. This study provides valuable insights into the hydrolysis process of borate networks, offering a detailed comparison between different computational approaches. The results demonstrate that the functionals B3LYP, PBE0, and wB97Xd closely approximated the reference MP2 and CCSD(T) calculated reaction pathways, both qualitatively in terms of the mechanism, and quantitatively in terms of the differences in the reaction barriers within the 0.1-0.2 eV interval for the most plausible reaction pathways. In addition, CAM-B3LYP also yielded acceptable results in all cases except for the most complicated pathway. These findings are useful for guiding further computational studies, including those employing machine learning approaches, and experimental investigations requiring accurate reference data for hydrolysis reactions in borate networks.

Defect-induced properties of MoSi2/Nb(Ta)Si2 disilicide nanocomposites

Research on disilicide nanocomposites, as modern materials with promising technological applications, is very desirable these days. Our ab initio analysis concentrates on the C11b (tetragonal) MoSi2/C40 (hexagonal) NbSi2 or TaSi2 nanocomposites containing 12 types of interfaces formed by (110) planes in the C11b and (0001) planes in the C40 disilicide. The most stable nanocomposites are MoSi2(AC)/Nb(Ta)Si2(BAC), MoSi2(AB)/Nb(Ta)Si2(CAB) and MoSi2(AB)/Nb(Ta)Si2(ABC). The interfaces reveal positive formation energies, e.g. γIFBA = 0.63670 J.m−2 and γIFCA = 0.63727 J.m−2 in the Nb system and γIFBA = 0.57837 J.m−2 and γIFCA = 0.57802 J.m−2 in the Ta system. In the most stable C11b-MoSi2(AC)/C40-Nb(Ta)Si2(BAC) nanocomposite, the effect of the impurities (Al, Si), vacancies or their aggregates on the stability and structure is investigated. It turns out that (i) vacancies preferentially form at the Si positions in the third (first) layer of MoSi2 in the Nb (Ta) systems, utilising an energy of 2.259 eV.Va−1 (1.971 eV.Va−1); (ii) Al impurities prefer Si positions, and it is easier to introduce them into the Ta system than into the Nb one; however, this does not apply if Al is in the Mo position; (iii) Si impurities prefer Ta positions to Nb ones, and the bulk to interfacial ones; (iv) the Si-Si divacancy is the least destabilising among divacancies; and (v) Al impurities in both systems prevent the formation of Si vacancies, and the Si impurities simplify the formation of vacancies in the Nb system. As there is very little experimental information on the structure and properties of these interfaces, most of the present results are theoretical predictions which may motivate future experimental work.