Ab Initio Calculations Research Articles

Isomeric effects on the electron impact scattering for selected five membered heterocyclic ring molecules

We present electron scattering cross-sectional data for selected isomers of the five-membered ring molecules, specifically oxazole and isoxazole, thiazole and isothiazole, and imidazole and pyrazole. The ab-initio R-matrix method, incorporating static exchange polarization approximations, is employed for this calculation from energy range 0.1 eV to 20 eV. Three shape resonances are identified and characterized in each system, consisting of two π* and one σ* shape resonances. Notably, thiazole and isothiazole exhibit additional σ* resonance which is which is at a lower energy than other σ* resonance. The calculated resonance positions align well with available experimental as well as theoretical data. We also performed electronic structure calculations to aid in characterization of resonances. Comparison of the scattering cross-sectional data with their respective isomers reveal marginal differences in the magnitude of the elastic cross section particularly below 1 eV. This discrepancy may be attributed to variations in the long-range electronic dipole contribution to the electron-molecule interaction process. Further, to understand dependency of dipole moment on elastic cross section, we performed a fitting procedure for the elastic cross sections at 0.1 eV with square of the dipole moment of all the five membered ring molecules studied here. The fitting formula so obtained was used to estimate the cross section for other three five membered ring molecules: Furan, Thiophene and Pyrrole. Additionally, total ionization cross sections are computed using the binary-encounter-Bethe (BEB) model, demonstrating nearly identical results when compared with their isomers. Our findings offer insights into the influence of structural changes on the electron scattering data, providing guidance for other theoretical investigations.

Comparative analysis of KXH3(X= Mg, be) hydride cubic perovskites for hydrogen storage properties: A computational approach

The burgeoning potential of hydrogen as a future clean energy source has spurred intense research into hydrogen storage solutions. Novel hydride perovskite materials aside metal hydride are at the forefront of this effort, engaging researchers worldwide. This study utilizes Ab-initio calculations based on density functional theory (DFT) implemented in VASP to compare the electrical, elastic, thermodynamic, and optical properties of cubic KXH3 (X = Mg, Be) compounds. Generalized gradient approximation (GGA) with the Perdew-Burke-Ernzrhof (PBE) scheme is employed for optimization. Our calculations agree well with previously reported results. However, the tolerance factor suggests KBeH3 may not be stable in the cubic form. The electronic structure reveals KMgH3 to be semiconductive, while KBeH3 exhibits metallic behavior. Both compounds exhibit mechanical stability within the study. Optical properties are also investigated, showing suitability for hydrogen storage in the low energy range. Additionally, the mechanical parameters satisfy the Born stability criterion, indicating good mechanical stability for both compounds. Finally, the gravimetric ratios for hydrogen storage are calculated as 5.86 wt% and 4.52 wt% for KMgH3 and KBeH3, respectively. These high values suggest both compounds hold significant promise for diverse renewable energy applications and long-term hydrogen fuel storage.

Ab initio framework for deciphering trade-off relationships in multi-component alloys

While first-principles methods have been successfully applied to characterize individual properties of multi-principal element alloys (MPEA), their use in searching for optimal trade-offs between competing properties is hampered by high computational demands. In this work, we present a framework to explore Pareto-optimal compositions by integrating advanced ab initio-based techniques into a Bayesian multi-objective optimization workflow, complemented by a simple analytical model providing straightforward analysis of trends. We benchmark the framework by applying it to solid solution strengthening and ductility of refractory MPEAs, with the parameters of the strengthening and ductility models being efficiently computed using a combination of the coherent-potential approximation method, accounting for finite-temperature effects, and actively-learned moment-tensor potentials parameterized with ab initio data. Properties obtained from ab initio calculations are subsequently used to extend predictions of all relevant material properties to a large class of refractory alloys with the help of the analytical model validated by the data and relying on a few element-specific parameters and universal functions that describe bonding between elements. Our findings offer crucial insights into the traditional strength-vs-ductility dilemma of refractory MPEAs. The proposed framework is versatile and can be extended to other materials and properties of interest, enabling a predictive and tractable high-throughput screening of Pareto-optimal MPEAs over the entire composition space.

Enhancing the Electrochemical Activity of 2D Materials Edges through Oriented Electric Fields.

The edges of 2D materials have emerged as promising electrochemical catalyst systems, yet their performance still lags behind that of noble metals. Here, we demonstrate the potential of oriented electric fields (OEFs) to enhance the electrochemical activity of 2D materials edges. By atomically engineering the edge of a fluorographene/graphene/MoS2 heterojunction nanoribbon, strong and localized OEFs were realized as confirmed by simulations and spatially resolved spectroscopy. The observed fringing OEF results in an enhancement of the heterogeneous charge transfer rate between the edge and the electrolyte by 2 orders of magnitude according to impedance spectroscopy. Ab initio calculations indicate a field-induced decrease in the reactant adsorption energy as the origin of this improvement. We apply the OEF-enhanced edge reactivity to hydrogen evolution reactions (HER) and observe a significantly enhanced electrochemical performance, as evidenced by a 30% decrease in Tafel slope and a 3-fold enhanced turnover frequency. Our findings demonstrate the potential of OEFs for tailoring the catalytic properties of 2D material edges toward future complex reactions.

Ab Initio Investigation of Tetrel Bonds in Isolated Complexes Formed Between a Lewis Acid H3MX, M-O or M-S (M = Si, Ge, or Sn) and the Lewis Bases B = N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O, and NH3.

Isolated complexes of the type B⋯A in which the noncovalent interaction is a tetrel bond have been characterized by ab initio calculations at the CCSD(T)(F12c)/cc-pVDZ-F12 level. The Lewis bases B involved were N2, CO, HCCH, PH3, C2H4, HCN, CS, HNC, NP, H2O and NH3. Two types of Lewis acid A were examined, each containing one of the tetrel atoms M = Si, Ge or Sn, The Lewis acids in the first series were the H3MX (X = F, Cl, CN, H), in each of which the most electrophilic region was found to lie on the C3 axis of the C3v molecules, near to the tetrel atom M. In the second series the Lewis acids were M-O and M-S. Graphs, consisting of calculated equilibrium dissociation energies De of each B⋯H3MX complex plotted against the nucleophilicities NB of the Lewis bases B, were used to obtain the electrophilicity EH3MX of each molecule H3MX (M = Si, Ge, Sn). The molecular electrostatic surface of potentials of the molecules M-S and M-O (M = Si, Ge, Sn) revealed that many of the B⋯M-S and B⋯M-O complexes should have a tetrel bond to M in which the axis of the M-S or M-O subunit should be approximately perpendicular to the axis of the nonbonding or π-bonding electron pair carried by B, a novel type of tetrel bond confirmed by geometry optimizations of the complexes.

MoSSe/Si9C15 heterojunction photodetectors with ultrahigh photocurrent and carrier mobility

The structural, electronic, optical properties and photogalvanic effect of MoSSe/Si9C15 and Si9C15/MoSSe heterostructures are investigated utilizing density functional theory. Band gaps of 1.70 eV and 1.03 eV are respectively exhibited by these heterostructures, both classified as direct bandgap semiconductors. The thermal stability of the MoSSe/Si9C15 and Si9C15/MoSSe heterostructures is demonstrated through ab initio molecular dynamics calculations. A hole mobility of 62774 cm2/Vs in the zigzag direction and an electron mobility of 1248 cm2/Vs in the armchair direction are recorded for the MoSSe/Si9C15 heterostructure. Light absorption in both the ultraviolet and visible light regions is observed for these heterostructures. Upon construction of a self-powered MoSSe/Si9C15 photodetector, a peak photocurrent (Jph) of 10.76 a02/photon is achieved, influenced by changes in polarization angle θ and photon energy, and a maximum extinction ratio of 26.7 is reached, showcasing high polarization sensitivity.

Why the pyrochlore-like antiferromagnet NaCu3F7 is magnetically non-frustrated

We present a theoretical study of the magnetic properties for the pyrochlore-like NaCu3F7 compound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated using ab-initio methods explicitly treating the electronic correlation. A model Hamiltonian (quantum Heisenberg Hamiltonian, and for comparison a spin 1/2 Ising Hamiltonian) was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field. The magnetic order at zero magnetic field is non frustrated and associated with the propagation vector q→=(0,0,0) . The magnetization versus magnetic field reveals the existence of a 1/3 plateau that could be observed in high-pulsed magnetic field experiments. Analyzing the magnetic interactions, we highlight the importance of the magnetic ion nature, and the lattice distortion, in the non-frustrated nature of the NaCu3F7 magnetic structure, despite its triangular/Kagome subnetworks. We believe that this non-frustrated behavior could also take place in other triangular copper-based systems.

Non-adiabatic electronic relaxation of tetracene from its brightest singlet excited state.

The ultrafast relaxation dynamics of tetracene following UV excitation to the bright singlet state S6 has been studied with time-resolved photoelectron spectroscopy. With the help of high-level abinitio multireference perturbation theory calculations, we assign photoelectron signals to intermediate dark electronic states S3, S4, and S5 as well as to a low-lying electronic state S2. The energetic structure of these dark states has not been determined experimentally previously. The time-dependent photoelectron yields assigned to the states S6, S5, and S4 have been analyzed and reveal the depopulation of S6 within 60fs, while S5 and S4 are populated with delays of about 50 and 80fs. The dynamics of the lower-lying states S3 and S2 seem to agree with a delayed population coinciding with the depopulation of the higher-lying states S4-S6 but could not be elucidated in full detail due to the low signal levels of the corresponding two-photon ionization probe processes.

Non-adiabatic electronic relaxation of tetracene from its brightest singlet excited state.

The ultrafast relaxation dynamics of tetracene following UV excitation to the bright singlet state S6 has been studied with time-resolved photoelectron spectroscopy. With the help of high-level abinitio multireference perturbation theory calculations, we assign photoelectron signals to intermediate dark electronic states S3, S4, and S5 as well as to a low-lying electronic state S2. The energetic structure of these dark states has not been determined experimentally previously. The time-dependent photoelectron yields assigned to the states S6, S5, and S4 have been analyzed and reveal the depopulation of S6 within 60fs, while S5 and S4 are populated with delays of about 50 and 80fs. The dynamics of the lower-lying states S3 and S2 seem to agree with a delayed population coinciding with the depopulation of the higher-lying states S4-S6 but could not be elucidated in full detail due to the low signal levels of the corresponding two-photon ionization probe processes.

The Effects on Stability and Electronic Structure of Si-Segregated θ′/Al Interface Systems in Al-Cu Alloys

This study systematically investigates the energy and electronic properties of Si-segregated θ′(Al2Cu)/Al semi-coherent and coherent interface systems in Al-Cu alloys using ab initio calculations. By evaluating the bonding strength at the interface, it has been revealed that Si segregated at the A1 site (Al slab) of the semi-coherent interface systems exhibits the most negative segregation energy, resulting in a noticeable decrease in total energy and an increase in interface adhesion. The electronic structure analysis indicates the presence of Al-Cu and Al-Al bonds, with Si occupying the A1 site. The strong bond formation between Al-Cu and Al-Al is essential for improving interface bonding strength. The results of the calculating analyses are consistent with the results of the previous experiments, and Si can be used as a synergistic element to reduce the θ′/Al interface energy and further reduce the coarsening drive of the θ′ precipitated phase, which can provide new perspectives and computational ideas for the compositional design of heat-resistant Al-Cu alloys.

Revealing a distortive polar order buried in the Fermi sea.

Polar metals are challenging to identify spectroscopically because the fingerprints of electric polarization are often obscured by the presence of screening charges. Here, we unravel unambiguous signatures of a distortive polar order buried in the Fermi sea by probing the nonlinear optical response of materials driven by tailored terahertz fields. We apply this strategy to investigate the topological crystalline insulator Pb1-xSnxTe, tracking its soft phonon mode in the time domain and observing the occurrence of inversion symmetry breaking as a function of temperature. By combining measurements across the material's phase diagram with ab initio calculations, we demonstrate the generality of our approach. These results highlight the potential of terahertz driving fields to reveal polar orders coexisting with itinerant electrons, thus opening additional avenues for material discovery.

An Atom-Precise Understanding of DNA-Stabilized Silver Nanoclusters.

ConspectusDNA-stabilized silver nanoclusters (AgN-DNAs) are sequence-encoded fluorophores. Like other noble metal nanoclusters, the optical properties of AgN-DNAs are dictated by their atomically precise sizes and shapes. What makes AgN-DNAs unique is that nanocluster size and shape are controlled by nucleobase sequence of the templating DNA oligomer. By choice of DNA sequence, it is possible to synthesize a wide range of AgN-DNAs with diverse emission colors and other intriguing photophysical properties. AgN-DNAs hold significant potential as "programmable" emitters for biological imaging due to their combination of small molecular-like sizes, bright and sequence-tuned fluorescence, low toxicities, and cost-effective synthesis. In particular, the potential to extend AgN-DNAs into the second near-infrared region (NIR-II) is promising for deep tissue imaging, which is a major area of interest for advancing biomedical imaging. Achieving this goal requires a deep understanding of the structure-property relationships that govern AgN-DNAs in order to design AgN-DNA emitters with sizes and geometries that support NIR-II emission.In recent years, major advances have been made in understanding the structure and composition of AgN-DNAs, enabling new insights into the correlation of nanocluster structure and photophysical properties. These advances have hinged on combined innovations in mass characterization and crystallography of compositionally pure AgN-DNAs, together with combinatorial experiments and machine learning-guided design. A combined approach is essential due to the major challenge of growing suitable AgN-DNA crystals for diffraction and to the labor-intensive nature of preparing and solving the molecular formulas of atomically precise AgN-DNAs by mass spectrometry. These approaches alone are not feasibly scaled to explore the large sequence space of DNA oligomer templates for AgN-DNAs.This account describes recent fundamental advances in AgN-DNA science that have been enabled by high throughput synthesis and fluorimetry together with detailed analytical studies of purified AgN-DNAs. First, short introductions to nanocluster chemistry and AgN-DNA basics are presented. Then, we review recent large-scale studies that have screened thousands of DNA templates for AgN-DNAs, leading to discovery of distinct classes of these emitters with unique cluster core compositions and ligand chemistries. In particular, the discovery of a new class of chloride-stabilized AgN-DNAs enabled the first ab initio calculations of AgN-DNA electronic structure and present new approaches to stabilize these emitters in biologically relevant conditions. Near-infrared (NIR) emissive AgN-DNAs are also found to exhibit diverse structures and properties. Finally, we conclude by highlighting recent proof-of-principle demonstrations of NIR AgN-DNAs for targeted fluorescence imaging. Continued efforts may future push AgN-DNAs into the tissue transparency window for fluorescence imaging in the NIR-II tissue transparency window.

Thermal Truncation of Heptamethine Cyanine Dyes.

Cyanine dyes are a class of organic, usually cationic molecules containing two nitrogen centers linked through conjugated polymethine chains. The synthesis and reactivity of cyanine derivatives have been extensively investigated for decades. Unlike the recently described phototruncation process, the thermal truncation (chain shortening) reaction is a phenomenon that has rarely been reported for these important fluorophores. Here, we present a systematic investigation of the truncation of heptamethine cyanines (Cy7) to pentamethine (Cy5) and trimethine (Cy3) cyanines via homogeneous, acid-base-catalyzed nucleophilic exchange reactions. We demonstrate how different substituents at the C3' and C4' positions of the chain and different heterocyclic end groups, the presence of bases, nucleophiles, and oxygen, solvent properties, and temperature affect the truncation process. The mechanism of chain shortening, studied by various analytical and spectroscopic techniques, was verified by extensive ab initio calculation, implying the necessity to model catalytic reactions by highly correlated wave function-based methods. In this study, we provide critical insight into the reactivity of cyanine polyene chains and elucidate the truncation mechanism and methods to mitigate side processes that can occur during the synthesis of cyanine derivatives. In addition, we offer alternative routes to the preparation of symmetrical and unsymmetrical meso-substituted Cy5 derivatives.

A database of high-pressure crystal structures from hydrogen to lanthanum

This paper introduces the HEX (High-pressure Elemental Xstals) database, a complete database of the ground-state crystal structures of the first 57 elements of the periodic table, from H to La, at 0, 100, 200 and 300 GPa. HEX aims to provide a unified reference for high-pressure research, by compiling all available experimental information on elements at high pressure, and complementing it with the results of accurate evolutionary crystal structure prediction runs based on Density Functional Theory. Besides offering a much-needed reference, our work also serves as a benchmark of the accuracy of current ab-initio methods for crystal structure prediction. We find that, in 98% of the cases in which experimental information is available, ab-initio crystal structure prediction yields structures which either coincide or are degenerate in enthalpy to within 300 K with experimental ones. The main manuscript contains synthetic tables and figures, while the Crystallographic Information File (cif) for all structures can be downloaded from the related figshare online repository.

Low energy electron scattering cross sections of cyanotriacetylene (HC7N) based on ab-initio R-matrix method

Cyanotriacetylene (HC7N) is a linear unsaturated molecule detected in various regions of space. In this present study, we explored the quantum dynamics of low-energy electron collisions with linear cyanopolyyne molecule (HC7N) to identify the locations and structural features of their metastable negative ions (also known as transient negative ions). We employed the R-matrix method for handling low-energy electron scattering studies. To uncover trends among cyanopolyynes molecules, we have also incorporated results from Cyanoacetylene (HC3N) and Cyanodiacetylene (HC5N). Notably, we observed that the number of π* resonances increases and shifts to lower energies as the number of triple bonds increases in higher-order molecules. Our theoretical calculations contain elastic, differential, and momentum cross-sections in the elastic part. Additionally, we calculated excitation and ionization cross-sections in the inelastic regime. This comprehensive theoretical data on electron scattering will be valuable for understanding the molecular chemistry involving this interesting molecule.

Electronic structure and spectroscopic properties of some low-lying electronic states of neutral and ionic species CN and CN−

ABSTRACT The present work provides Potential Energy Curves (PECs) of both cyano radical CN and cyanide anion CN − up to the third asymptote of dissociation out of ab initio calculations. The [MRCI+Q] method is the level of theory used here and we have associated it with the Dunning basis set AV6Z (Augmented correlation-consistent polarised Valence sextet Zeta) for geometry optimisation of our systems. Electronic configurations of the states of the two species were explored and based on these configurations and the relative positions of the PECs of CN − against those of the neutral radical CN, stable and metastable states have been found and exhibited. The calculated electron affinity here that proves itself to be positive and the position of the X 1 Σ + state against its corresponding neutral parent state ( X 2 Σ + ) from which it derives led to confirm that this state is a long-lived and stable ground state of the cyanide anion CN − . Spectroscopic constants of both ground and low-lying excited states are calculated and exhibited in this work.

Ab Initio Prediction of Vapor Pressure for Diverse Atomic Layer Deposition Precursors.

Understanding the saturated vapor pressure (Pvap) is vital for evaluating atomic layer deposition (ALD) precursors, as it directly influences the ALD temperature window and, by extension, the processability of compounds. The early estimation of vapor pressure ranges is crucial during the initial stages of novel precursor design, reducing the reliance on empirical synthesis or experimentation. However, predicting vapor pressure through computer simulations is often impeded by the scarcity of suitable empirical force fields for molecular dynamics simulations. This challenge is further compounded by the diverse chemical substances and the introduction of new elements into modern ALD processes, necessitating robust force fields that can accommodate metals, organics, and halides. In response, this study introduces a novel approach utilizing a quantum mechanically derived force field for the prediction of vapor pressure across a wide spectrum of potential ALD precursors. This approach enables the creation of system-specific force fields through parametrization based on ab initio calculations for a single molecule. We develop a comprehensive workflow to simulate both liquid and gaseous equilibrium phases, allowing the calculation of vapor pressure across a wide temperature range. Our methodology has been validated with a diverse set of ALD precursors, demonstrating its robustness in predicting Pvap at specified temperatures. The approach yields a Pearson's correlation coefficient (R2) greater than 0.9 on a logarithmic scale and a root-mean-squared deviation in self-solvation-free energies as low as 1.3 kcal mol-1. This innovative workflow, which does not require any prior experimental data, marks a significant advancement in the computer-aided design of novel ALD precursors, paving the way for accelerating developments in technology.

Similarities and Differences of Hydridic and Protonic Hydrogen Bonding.

Ab initio calculations were employed to investigate the interactions between selected electron-donating groups, characterized by M-H bonds (where M represents a transition metal and H denotes a hydridic hydrogen), and electron-accepting groups featuring both σ- and π-holes. The study utilized the ωB97X-D3BJ/def2-TZVPPD level of theory. Hydridic hydrogen complexes were found in all complexes with σ- and π-holes. A comparative analysis was conducted on the properties hydridic H-bond complexes, presented here and those studied previously, alongside an extended set of protonic H-bonds complexes. While the stabilization energies changes in M-H bond lengths, vibrational frequencies, intensities of the spectral bands, and charge transfer for these complexes are comparable, the nature of hydridic and protonic H-bonds fundamentally differ. In protonic H-bond complexes, the main stabilization forces arise from electrostatic contributions, while in hydridic H-bond complexes, dispersion energy, is the primary stabilization factor due to the excess of electrons and thus larger polarizability at hydridic H. The finding represents an important characteristic that distinguishes hydridic H-bonding from protonic H-bonds.

Quantum Mechanics Characterization of Non-Covalent Interaction in Nucleotide Fragments

Accurate calculation of non-covalent interaction energies in nucleotides is crucial for understanding the driving forces governing nucleic acid structure and function, as well as developing advanced molecular mechanics forcefields or machine learning potentials tailored to nucleic acids. Here, we dissect the nucleotides’ structure into three main constituents: nucleobases (A, G, C, T, and U), sugar moieties (ribose and deoxyribose), and phosphate group. The interactions among these fragments and between fragments and water were analyzed. Different quantum mechanical methods were compared for their accuracy in capturing the interaction energy. The non-covalent interaction energy was decomposed into electrostatics, exchange-repulsion, dispersion, and induction using two ab initio methods: Symmetry-Adapted Perturbation Theory (SAPT) and Absolutely Localized Molecular Orbitals (ALMO). These calculations provide a benchmark for different QM methods, in addition to providing a valuable understanding of the roles of various intermolecular forces in hydrogen bonding and aromatic stacking. With SAPT, a higher theory level and/or larger basis set did not necessarily give more accuracy. It is hard to know which combination would be best for a given system. In contrast, ALMO EDA2 did not show dependence on theory level or basis set; additionally, it is faster.

Achieving High Substitutional Incorporation in Mn-Doped Graphene.

Despite its broad potential applications, substitution of carbon by transition metal atoms in graphene has so far been explored only to a limited extent. We report the realization of substitutional Mn doping of graphene to a record high atomic concentration of 0.5%, which was achieved using ultralow-energy ion implantation. By correlating the experimental data with the results of ab initio Born-Oppenheimer molecular dynamics calculations, we infer that direct substitution is the dominant mechanism of impurity incorporation. Thermal annealing in ultrahigh vacuum provides efficient removal of surface contaminants and additional implantation-induced disorder, resulting in Mn-doped graphene that, aside from the substitutional Mn impurities, is essentially as clean and defect-free as the as-grown layer. We further show that the Dirac character of graphene is preserved upon substitutional Mn doping, even in this high concentration regime, making this system ideal for studying the interaction between Dirac conduction electrons and localized magnetic moments. More generally, these results show that ultralow energy ion implantation can be used for controlled functionalization of graphene with substitutional transition-metal atoms, of relevance for a wide range of applications, from magnetism and spintronics to single-atom catalysis.