Active Learning of Atomic Size Gas/Solid Potential Energy Surfaces via Physics Aware Models.

We propose an active learning (AL) framework to develop classical force fields (FFs) that accurately model the potential energy surfaces (PES) of gas/solid atomic-scale complexes. A central challenge is integrating AL with flexible, computationally efficient physics-aware potentials to achieve quantum-level accuracy for complex interfacial systems. Our approach trains physics-aware potentials, with incorporated flexibility and smoothness, on actively sampled density functional theory (DFT) data to describe interactions between undercoordinated atomic silver (Ag) clusters and gaseous pollutants (CO, CO, SO), relevant for environmental applications like sensing.

Thermal processes and secondary recycling regulate the atmospheric levels of the highly toxic polychlorinated naphthalenes in the urban environment of Eastern Mediterranean and Middle East.

Although production of legacy industrial-grade persistent organic pollutants has been prohibited since the early 2000's, residues persist across all environmental compartments, with unintentional releases still documented globally. The present work explores comprehensively the atmospheric occurrence and fate of the scarcely monitored polychlorinated naphthalenes (PCNs), along with polybrominated diphenyl ethers (PBDEs), in the urban environment of Eastern Mediterranean and Middle East. Gaseous and particulate phase concentrations of PCNs and PBDEs (fifty-six and twelve congeners) were comparable to urban locations in the broader region.

Room temperature ferroelectricity and an electrically tunable Berry curvature dipole in III-V monolayers.

Two-dimensional ferroelectric monolayers are promising candidates for compact memory devices and flexible electronics. Here, through first-principles calculations, we predict room temperature ferroelectricity in AB-type monolayers comprising group III (A = Al, In, Ga) and group V (B = As, P, Sb) elements. We show that their spontaneous polarization, oriented out-of-plane, ranges from 9.

Electronic properties and collision cross sections of AgOH (, = 1-4) aerosol ionic clusters.

Experimental evidence shows that hydroxylated metal ions are often produced during cluster synthesis by atmospheric pressure spark ablation. In this work, we predict the ground state equilibrium structures of AgOH clusters ( and = 1-4), which are readily produced when spark ablating Ag, using the coupled cluster with singles and doubles (CCSD) method. The stabilization energy of these clusters is calculated with respect to the dissociation channel having the lowest energy, by accounting perturbative triples corrections to the CCSD method.

Kinetic study of the CN + CH hydrogen abstraction reaction based on an analytical potential energy surface.

The temperature dependence of the thermal rate constants and kinetic isotope effects (KIE) of the CN + CH gas-phase hydrogen abstraction reaction was theoretically determined within the 25-1000 K temperature range, , from very low- to high-temperature regimes. Based on a recently developed full-dimensional analytical potential energy surface fitted to highly accurate explicitly correlated calculations, three different kinetic theories were used: canonical variational transition state theory (CVT), quasiclassical trajectory theory (QCT), and ring polymer molecular dynamics (RPMD) method for the computation of rate constants. We found that the thermal rate constants obtained with the three theories show a V-shaped temperature dependence, with a pronounced minimum near 200 K, qualitatively reproducing the experimental measurements.

Adsorption of air pollutants onto silver and gold atomic clusters: DFT and PNO-LCCSD-F12 calculations.

We provide a comprehensive investigation of intermolecular interactions between atmospheric gaseous pollutants, including CH, CO, CO, NO, NO, SO, as well as HO and Ag ( = 1-22) or Au ( = 1-20) atomic clusters. The optimized geometries of all the systems investigated in our study were determined using density functional theory (DFT) with M06-2X functional and SDD basis set. The PNO-LCCSD-F12/SDD method was used for more accurate single-point energy calculations.

Gas-Phase Interaction of CO, CO, HS, NH, NO, NO, and SO with ZnO and Zn Atomic Clusters.

Atmospheric pollutants pose a high risk to human health, and therefore it is necessary to capture and preferably remove them from ambient air. In this work, we investigate the intermolecular interaction between the pollutants such as CO, CO, HS, NH, NO, NO, and SO gases with the Zn and ZnO atomic clusters, using the density functional theory (DFT) at the meta-hybrid functional TPSSh and LANl2Dz basis set. The adsorption energy of these gas molecules on the outer surfaces of both types of clusters has been calculated and found to have a negative value, indicating a strong molecular-cluster interaction.

Electronic Structure, Stability, and Electrical Mobility of Cationic Silver Oxide Atomic Clusters.

Silver oxide cluster cations (AgO) can readily be produced by a number of methods including atmospheric-pressure spark ablation of pure silver electrodes when trace amounts of oxygen are present in the carrier gas. Here we determine the equilibrium geometries of AgO clusters ( = 1-4; = 1-5) using accurate coupled cluster with singles and doubles (CCSD) method, while the stabilization energies are calculated with additional perturbative triples correction (CCSD(T)). Although a number of stable states have been identified, our results show that the AgO clusters with = 1 are more stable than those with ≥ 2 due to the absence of the terminally attached O molecule, corroborating recent observations by mass spectrometry.

Large and anisotropic carrier mobility in monolayers of the MAZ series (M = Cr, Mo, W; A = Si, Ge; and Z = N, P).

The recent discovery of synthetic two-dimensional materials has opened up a new paradigm for exploring novel transport and optical properties, beyond those found in naturally occurring materials. Here, we present a detailed investigation of the acoustic phonon limited intrinsic carrier mobility in MAZ series (M = Cr, Mo, W; A = Si, Ge; and Z = N, P) monolayers. We find that out of the twelve monolayers studied, only two are metallic (CrGeN and CrGeP), and the rest of them are semiconducting.

Experimental and theoretical studies of the gas-phase reactions of O(D) with HO and DO at low temperature.

Here we report the results of an experimental and theoretical study of the gas-phase reactions between O(D) and HO and O(D) and DO at room temperature and below. On the experimental side, the kinetics of these reactions have been investigated over the 50-127 K range using a continuous flow Laval nozzle apparatus, coupled with pulsed laser photolysis and pulsed laser induced fluorescence for the production and detection of O(D) atoms respectively. Experiments were also performed at 296 K in the absence of a Laval nozzle.

Isotopic separation of helium through graphyne membranes: a ring polymer molecular dynamics study.

Microscopic-level understanding of the separation mechanism for two-dimensional (2D) membranes is an active area of research due to potential implications of this class of membranes for various technological processes. Helium (He) purification from the natural resources is of particular interest due to the shortfall in its production. In this work, we applied the ring polymer molecular dynamics (RPMD) method to graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes having variable pore sizes for the separation of He isotopes, and compare for the first time with rigorous quantum calculations.

Temperature-Dependent Superplasticity and Strengthening in CoNiCrFeMn High Entropy Alloy Nanowires Using Atomistic Simulations.

High strength and ductility, often mutually exclusive properties of a structural material, are also responsible for damage tolerance. At low temperatures, due to high surface energy, single element metallic nanowires such as Ag usually transform into a more preferred phase via nucleation and propagation of partial dislocation through the nanowire, enabling superplasticity. In high entropy alloy (HEA) CoNiCrFeMn nanowires, the motion of the partial dislocation is hindered by the friction due to difference in the lattice parameter of the constituent atoms which is responsible for the hardening and lowering the ductility.

VTST and RPMD kinetics study of the nine-body X + CH (X ≡ H, Cl, F) reactions based on analytical potential energy surfaces.

Thermal rate constants of nine-atom hydrogen abstraction reactions, X + C2H6 → HX + C2H5 (X ≡ H, Cl, F) with qualitatively different reaction paths, have been investigated using two kinetics approaches - variational transition state theory with multidimensional tunnelling (VTST/MT) and ring polymer molecular dynamics (RPMD) - and full dimensional analytical potential energy surfaces. For the H + C2H6 reaction, which proceeds through a noticeable barrier height of 11.62 kcal mol-1, kinetics approaches showed excellent agreement between them (with differences less than 30%) and with the experiment (with differences less than 60%) in the wide temperature range of 200-2000 K.

Effect of B-site cation ordering on high temperature thermoelectric behavior of Ba Sr TiFeO double perovskites.

Here, we have reported the detailed structural analysis in correlation with thermoelectric properties of Ba doped SrTiFeO (BSTF) double perovskites in the temperature range from 300 K to 1100 K. BSTF compositions exhibit single phase cubic structure with [Formula: see text] crystal symmetry from room temperature to 523 K and also at temperature beyond 923K. Rietveld refinement of high temperature XRD data suggests the coexistence of two cubic phases with [Formula: see text] space group having same composition in the intermediate temperature region.

Dynamics of H + HeH( = 0, = 0) → H + He: Insight on the Possible Complex-Forming Behavior of the Reaction.

The H + HeH→ He + H reaction has been studied by means of a combination of theoretical approaches: a statistical quantum method (SQM), ring polymer molecular dynamics (RPMD), and the quasiclassical trajectory (QCT) method. Cross sections and rate constants have been calculated in an attempt to investigate the dynamics of the process. The comparison with previous calculations and experimental results reveals that despite the fact that statistical predictions seem to reproduce some of the overall observed features, the analysis at a more detailed state-to-state level shows noticeable deviations from a complex-forming dynamics.

Experimental and Theoretical Study of the O(D) + HD Reaction.

This work addresses the kinetics and dynamics of the gas-phase reaction between O(D) and HD molecules down to low temperature. Here, measurements were performed by using a supersonic flow (Laval nozzle) reactor coupled with pulsed laser photolysis for O(D) production and pulsed-laser-induced fluorescence for O(D) detection to obtain rate constants over the 50-300 K range. Additionally, temperature-dependent branching ratios (OD + H/OH + D) were obtained experimentally by comparison of the H/D atom atom yields with those of a reference reaction.

The low temperature D + H→ HD + H reaction rate coefficient: a ring polymer molecular dynamics and quasi-classical trajectory study.

The reaction between D and H plays an important role in astrochemistry at low temperatures and also serves as a prototype for a simple ion-molecule reaction. Its ground X[combining tilde]A' state has a very small thermodynamic barrier (up to 1.8 × 10 eV) and the reaction proceeds through the formation of an intermediate complex lying within the potential well with a depth of at least 0.

Polymorphs of two dimensional phosphorus and arsenic: insight from an evolutionary search.

Using an evolutionary algorithm, in conjunction with density functional theory (DFT) based electronic, ionic and cell relaxation, we perform an extensive search for the crystal structures of possible two dimensional (2D) allotropes of phosphorus and arsenic. In addition to previously reported allotropes like α, β, γ and δ, we discover four new allotropes, whose cohesive energies differ from that of the ground state (α and β, in the case of P and As, respectively) by merely ∼2-10 meV per atom. In terms of electrical properties, all of them are semiconductors, although the magnitude and nature of the bandgap (direct/indirect) vary considerably.

Potential energy surfaces of the electronic states of Li2F and Li2F(.).

The potential energy surfaces of the ground and low-lying excited states for the insertion reaction of atomic fluorine (F) and fluoride (F(-)) into the dilithium (Li2) molecule have been investigated. We have carried out explicitly correlated multi-reference configuration interaction (MRCI-F12) calculations using Dunning's augmented correlation-consistent basis sets. For the neutral system, the insertion of F into Li2 proceeds via a harpoon-type mechanism on the ground state surface, involving a covalent state and an ionic state which avoid each other at long distance.

First principles prediction of amorphous phases using evolutionary algorithms.

We discuss the efficacy of evolutionary method for the purpose of structural analysis of amorphous solids. At present, ab initio molecular dynamics (MD) based melt-quench technique is used and this deterministic approach has proven to be successful to study amorphous materials. We show that a stochastic approach motivated by Darwinian evolution can also be used to simulate amorphous structures.

Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe.

The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase distribution using the aberration-corrected optics of a scanning transmission electron microscope. The required phase distribution of the probe depends on the magnetic symmetry and crystal structure of the sample.

Boundaries for efficient use of electron vortex beams to measure magnetic properties.

Development of experimental techniques for characterization of magnetic properties at high spatial resolution is essential for progress in miniaturization of magnetic devices, for example, in data storage media. Inelastic scattering of electron vortex beams (EVBs) was recently reported to contain atom-specific magnetic information. We develop a theoretical description of inelastic scattering of EVBs on crystals and perform simulations for EVBs of different diameters.

Investigation of dissociative electron attachment to 2'-deoxycytidine-3'-monophosphate using DFT method and time dependent wave packet approach.

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2'-deoxycytidine-3'-monophosphate [3'-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.

Polymorphism of two-dimensional boron.

The structural stability and diversity of elemental boron layers are evaluated by treating them as pseudoalloy B(1-x)[hexagon](x), where [hexagon] is a vacancy in the close-packed triangular B lattice. This approach allows for an elegant use of the cluster expansion method in combination with first-principles density-functional theory calculations, leading to a thorough exploration of the configurational space. A finite range of compositions x is found where the ground-state energy is essentially independent of x, uncovering a variety of stable B-layer phases (all metallic) and suggesting polymorphism, in stark contrast to graphene or hexagonal BN.

Low-energy electron-induced single strand breaks in 2'-deoxycytidine-3'-monophosphate using the local complex potential based time-dependent wave packet approach.

Recent experimental and theoretical investigations on resonant electron scattering off DNA and DNA fragments using low-energy electrons (LEEs), to propose the mechanism for single strand breaks (SSBs) and double strand breaks (DSBs), have received considerable attention. It is our purpose here to understand theoretically the comprehensive route to SSB in a selected DNA fragment, namely, 2'-deoxycytidine-3'-monophosphate (3'-dCMPH), induced by LEE (0-3 eV) scattering using the local complex potential based time-dependent wave packet (LCP-TDWP) approach. To the best of our knowledge, there is no time-dependent quantum mechanical study that has been reported in the literature for this DNA fragment to date.