Accuracy, transferability, and computational efficiency of interatomic potentials for simulations of carbon under extreme conditions.

Large-scale atomistic molecular dynamics (MD) simulations provide an exceptional opportunity to advance the fundamental understanding of carbon under extreme conditions of high pressures and temperatures. However, the fidelity of these simulations depends heavily on the accuracy of classical interatomic potentials governing the dynamics of many-atom systems. This study critically assesses several popular empirical potentials for carbon, as well as machine learning interatomic potentials (MLIPs), in their ability to simulate a range of physical properties at high pressures and temperatures, including the diamond equation of state, its melting line, shock Hugoniot, uniaxial compressions, and the structure of liquid carbon.

Ice Phase Classification Made Easy with Score-Based Denoising.

Accurate identification of ice phases is essential for understanding various physicochemical phenomena. However, such classification for structures simulated with molecular dynamics is complicated by the complex symmetries of ice polymorphs and thermal fluctuations. For this purpose, both traditional order parameters and data-driven machine learning approaches have been employed, but they often rely on expert intuition, specific geometric information, or large training data sets.

Unraveling the Correlation between the Interface Structures and Tunable Magnetic Properties of LaSrCoO/LaSrMnO Bilayers Using Deep Learning Models.

Perovskite oxides are gaining significant attention for use in next-generation magnetic and ferroelectric devices due to their exceptional charge transport properties and the opportunity to tune the charge, spin, lattice, and orbital degrees of freedom. Interfaces between perovskite oxides, exemplified by LaSrCoO/LaSrMnO (LSCO/LSMO) bilayers, exhibit unconventional magnetic exchange switching behavior, offering a pathway for innovative designs in perovskite oxide-based devices. However, the precise atomic-level stoichiometric compositions and chemophysical properties of these interfaces remain elusive, hindering the establishment of surrogate design principles.

Dangling Bonds as Possible Contributors to Charge Noise in Silicon and Silicon-Germanium Quantum Dot Qubits.

Spin qubits based on Si and SiGe quantum dot architectures exhibit among the best coherence times of competing quantum computing technologies, yet they still suffer from charge noise that limit their qubit gate fidelities. Identifying the origins of these charge fluctuations is therefore a critical step toward improving Si quantum-dot-based qubits. Here, we use hybrid functional calculations to investigate possible atomistic sources of charge noise, focusing on charge trapping at Si and Ge dangling bonds (DBs).

Role of ripples in altering the electronic and chemical properties of graphene.

Ripples of graphene are known to manipulate electronic and hydrogenation properties of graphitic materials. More detailed work is needed to elucidate the structure-property relationship of these systems. In this work, the density functional theory is used to compute the energy and electronic structure of the graphene models with respect to variable curvatures and hydrogen adsorption sites.

Probing Charge Dynamics in Diamond with an Individual Color Center.

Control over the charge states of color centers in solids is necessary to fully utilize them in quantum technologies. However, the microscopic charge dynamics of deep defects in wide-band-gap semiconductors are complex, and much remains unknown. We utilize a single-shot charge-state readout of an individual nitrogen-vacancy (NV) center to probe the charge dynamics of the surrounding defects in diamond.

Incident wavelength and polarization dependence of spectral shifts in β-GaO UV photoluminescence.

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-GaO bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.

Anomalous diffusion along metal/ceramic interfaces.

Interface diffusion along a metal/ceramic interface present in numerous energy and electronic devices can critically affect their performance and stability. Hole formation in a polycrystalline Ni film on an α-AlO substrate coupled with a continuum diffusion analysis demonstrates that Ni diffusion along the Ni/α-AlO interface is surprisingly fast. Ab initio calculations demonstrate that both Ni vacancy formation and migration energies at the coherent Ni/α-AlO interface are much smaller than in bulk Ni, suggesting that the activation energy for diffusion along coherent Ni/α-AlO interfaces is comparable to that along (incoherent/high angle) grain boundaries.

Perfect Strain Relaxation in Metamorphic Epitaxial Aluminum on Silicon through Primary and Secondary Interface Misfit Dislocation Arrays.

Understanding the atomically precise arrangement of atoms at epitaxial interfaces is important for emerging technologies such as quantum materials that have function and performance dictated by bonds and defects that are energetically active on the micro-electronvolt scale. A combination of atomistic modeling and dislocation theory analysis describes both primary and secondary dislocation networks at the metamorphic Al/Si (111) interface, which is experimentally validated by atomic resolution scanning transmission electron microscopy. The electron microscopy images show primary misfit dislocations for the majority of the strain relief and evidence of a secondary structure allowing for complete relaxation of the Al-Si misfit strain.

TopoMS: Comprehensive topological exploration for molecular and condensed-matter systems.

We introduce TopoMS, a computational tool enabling detailed topological analysis of molecular and condensed-matter systems, including the computation of atomic volumes and charges through the quantum theory of atoms in molecules, as well as the complete molecular graph. With roots in techniques from computational topology, and using a shared-memory parallel approach, TopoMS provides scalable, numerically robust, and topologically consistent analysis. TopoMS can be used as a command-line tool or with a GUI (graphical user interface), where the latter also enables an interactive exploration of the molecular graph.

Descriptor-Based Approach for the Prediction of Cation Vacancy Formation Energies and Transition Levels.

Point defects largely determine the observed optical and electrical properties of a given material, yet the characterization and identification of defects has remained a slow and tedious process, both experimentally and theoretically. We demonstrate a computationally-cheap model that can reliably predict the formation energies of cation vacancies as well as the location of their electronic states in a large set of II-VI and III-V materials using only parameters obtained from the bulk primitive unit cell (2-4 atoms). We apply our model to ordered alloys within the CdZnSeTe, CdZnS, and ZnMgO systems and predict the positions of cation vacancy charge-state transition levels with a mean absolute error of < 0.

Stability of CdZnOS Quaternary Alloys Assessed with First-Principles Calculations.

One route to decreasing the absorption in CdS buffer layers in Cu(In,Ga)Se and CuZnSn(S,Se) thin-film photovoltaics is by alloying. Here we use first-principles calculations based on hybrid functionals to assess the energetics and stability of quaternary Cd, Zn, O, and S (CdZnOS) alloys within a regular solution model. Our results identify that full miscibility of most CdZnOS compositions and even binaries like Zn(O,S) is outside typical photovoltaic processing conditions.

Lithium ion solvation and diffusion in bulk organic electrolytes from first-principles and classical reactive molecular dynamics.

Lithium-ion battery performance is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact both the solvation and diffusivity of Li ions. In this work, we used first-principles molecular dynamics to examine the solvation and diffusion of Li ions in the bulk organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and a mixture of EC and EMC.

Identification of the local sources of paramagnetic noise in superconducting qubit devices fabricated on α-Al2O3 substrates using density-functional calculations.

Effective methods for decoupling superconducting qubits (SQs) from parasitic environmental noise sources are critical for increasing their lifetime and phase fidelity. While considerable progress has been made in this area, the microscopic origin of noise remains largely unknown. In this work, first principles density functional theory calculations are employed to identify the microscopic origins of magnetic noise sources in SQs on an α-Al2O3 substrate.

Simultaneous control of ionic and electronic conductivity in materials: thallium bromide case study.

Achieving simultaneous control of ionic and electronic conductivity in materials is one of the great challenges in solid state ionics. Since these properties are intertwined, optimizing one often results in degrading the other. In this Letter, we propose a method to limit ionic current without impacting the electronic properties of a general class of materials, based on codoping with oppositely charged ions.

Atomistic design of thermoelectric properties of silicon nanowires.

We present predictions of the thermoelectric figure of merit ( ZT) of Si nanowires with diameter up to 3 nm, based upon the Boltzman transport equation and ab initio electronic structure calculations. We find that ZT depends significantly on the wire growth direction and surface reconstruction, and we discuss how these properties can be tuned to select silicon based nanostructures with combined n-type and p-type optimal ZT. Our calculations show that only by reducing the ionic thermal conductivity by about 2 or 3 orders of magnitudes with respect to bulk values, one may attain ZT larger than 1, for 1 or 3 nm wires, respectively.

Nearest-neighbor configuration in (GaIn)(NAs) probed by x-ray absorption spectroscopy.

Ga(1-x)In(x)N(y)As(1-y) is a promising material system for the fabrication of inexpensive "last-mile" optoelectronic components. However, details of its atomic arrangement and the relationship to observed optical properties is not fully known. Particularly, a blueshift of emission wavelength is observed after annealing.