Hexagonal Boron Nitride Quantum Simulator: Prelude to Spin and Photonic Qubits.

The quest for qubit operation at room temperature is accelerating the field of quantum information science and technology. Solid state quantum defects with spin-optical properties are promising spin- and photonic qubit candidates for room temperature operations. In this regard, a single boron vacancy within hexagonal boron nitride (h-BN) lattice such as defect has coherent quantum interfaces for spin and photonic qubits owing to the large band gap of h-BN (6 eV) that can shield a computational subspace from environmental noise.

Enhanced Piezoelectric Response at Nanoscale Vortex Structures in Ferroelectrics.

The piezoelectric response is a measure of the sensitivity of a material's polarization to stress or its strain to an applied field. Using X-ray Bragg coherent diffraction imaging, we observe that topological vortices are the source of a 5-fold enhancement of the piezoelectric response near the vortex core. The vortices form where several low-symmetry ferroelectric phases and phase boundaries coalesce.

Enhanced carrier densities in two-dimensional electron gas formed at BaSnO/SrTaOand SrSnO/SrTaOinterfaces.

Two-dimensional electron gases (2DEGs) realized at perovskite oxide interfaces offer great promise for high charge carrier concentrations and low-loss charge transport. BaSnO(BSO) and SrSnO(SSO) are well-known wide bandgap semiconductors for their high mobility due to the Sn--dominated conduction band minimum (CBM). Tawith a 5valence configuration in SrTaO(STaO) injects theelectron across the interface into the unoccupied Snstates in BSO and SSO.

High Mobility Two-Dimensional Electron Gas at the BaSnO/SrNbO Interface.

Oxide two-dimensional electron gases (2DEGs) promise high charge carrier concentrations and low-loss electronic transport in semiconductors such as BaSnO (BSO). ACBN0 computations for BSO/SrNbO (SNO) interfaces show Nb- electron injection into extended Sn- electronic states. The conduction band minimum consists of Sn- states ∼1.

Molybdenum Disorder in Hydrated Sedovite, Ideally U(MoO)·HO, a Microporous Nanocrystalline Mineral Characterized by Three-Dimensional Electron Diffraction, Density Functional Theory Computations, and Complexity Analysis.

Sedovite, U(MoO)·HO, is reported as being one of the earliest supergene minerals formed of the secondary zone. The difficulty of isolating enough pure material limits studies to techniques that can access the nanoscale combined with theoretical analyses. The crystal structure of sedovite has been solved and refined using the dynamical approach from three-dimensional electron diffraction data collected on natural nanocrystals found among iriginite.

Layer dependent magnetism and topology in monolayer and bilayers Re(Br, I).

The realization of robust intrinsic ferromagnetism in two-dimensional materials with the possibility to support topologically non-trivial states has provided the fertile ground for novel physics and next-generation spintronics and quantum computing applications. In this contribution, we investigated the formation of topological states and magnetism in monolayer and bilayer systems of Re(= Br, I), with PBE, ACBN0 (self-consistent Hubbard-), excluding/including van der Waals (vdW) corrections and/or spin-orbit coupling. Bulk Re(= Br, I) is predicted to crystallize in space groupR3¯(#148), similar to CrI, with monolayer exfoliation energies that are comparable or less than that of graphite.

Magnetocaloric Effect in a Frustrated Gd-Garnet with No Long-Range Magnetic Order.

In this paper, the hyperkagome lattice of Gd spins in a garnet compound, GdCrGaO, is studied using bulk measurements and density functional computations, and the observation of large magnetocaloric effect corresponding to an entropy change, Δ = 45 J kgK (≈ 45 J molK) at 2 K, 8 T is reported. Though the compound defies long-range magnetic order down to 0.4 K, a broad feature below 10 K is observed in the specific heat with two low temperature anomalies at * ≈ 0.

Hydrogen bonding in the crystal structure of phurcalite, Ca[(UO)O(PO)]·7HO: single-crystal X-ray study and TORQUE calculations.

The crystal structure of phurcalite, Ca[(UO)O(PO)]·7HO, orthorhombic, a = 17.3785 (9) Å, b = 15.9864 (8) Å, c = 13.

Does β-PbO harbor topological states?

The electronic properties of β-PbO, have been controversial for several decades. Experiments find behavior ranging from metallic, attributed to oxygen vacancies, to indirect semiconducting for stoichiometric samples with a gap of 0.61 eV.

Crystal structure of vyacheslavite, U(PO)(OH), solved from natural nanocrystal: a precession electron diffraction tomography (PEDT) study and DFT calculations.

The crystal structure of the U(iv)-phosphate mineral vyacheslavite has been solved from precession electron diffraction tomography (PEDT) data from the natural nano-crystal and further refined using density-functional theory (DFT) calculations. Vyacheslavite is orthorhombic, with the space group , with ≈ 6.96 Å, ≈ 9.

Revealing hydrogen atoms in a highly-absorbing material: an X-ray diffraction study and Torque method calculations for lead-uranyl-oxide mineral curite.

The crystal structure of lead uranyl-oxide hydroxy-hydrate mineral curite, ideally Pb(HO)[(UO)O(OH)], was studied by means of single-crystal X-ray diffraction and theoretical calculations in order to localize positions of hydrogen atoms in the structure. This study has demonstrated that hydrogen atoms can be localized successfully also in materials for which the conventional approach of structure analysis failed, here due to very high absorption of X-rays by the mineral matrix. The theoretical calculations, based on the Torque method, provide a robust, fast real-space method for determining HO orientations from their rotational equilibrium condition.

Computational and experimental evidence for a new TM-N3/C moiety family in non-PGM electrocatalysts.

In the present work, we demonstrate that the formation energies of previously unexplored single and double carbon vacancy based TM-N3/C defect moieties are favourable. This prediction suggests that these defect motifs, in particular DV-Fe-N3/C can form during high-temperature catalyst synthesis. Defect specific N 1s core-level shifts were computed from first-principles for the deconvolution of XPS observations.

Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina.

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant γ-alumina supports.

Applicability of density functional theory in reproducing accurate vibrational spectra of surface bound species.

The structural equilibrium parameters, the adsorption energies, and the vibrational frequencies of the nitrogen molecule and the hydrogen atom adsorbed on the (111) surface of rhodium have been investigated using different generalized-gradient approximation (GGA), nonlocal correlation, meta-GGA, and hybrid functionals, namely, Perdew, Burke, and Ernzerhof (PBE), Revised-RPBE, vdW-DF, Tao, Perdew, Staroverov, and Scuseria functional (TPSS), and Heyd, Scuseria, and Ernzerhof (HSE06) functional in the plane wave formalism. Among the five tested functionals, nonlocal vdW-DF and meta-GGA TPSS functionals are most successful in describing energetics of dinitrogen physisorption to the Rh(111) surface, while the PBE functional provides the correct chemisorption energy for the hydrogen atom. It was also found that TPSS functional produces the best vibrational spectra of the nitrogen molecule and the hydrogen atom on rhodium within the harmonic formalism with the error of -2.

A density functional theory study of oxygen reduction reaction on non-PGM Fe-Nx-C electrocatalysts.

First-principles density functional theory (DFT) calculations were performed to explain the stability of catalytically active sites in Fe-Nx-C electrocatalysts, their ORR activity and ORR mechanism. The results show that the formation of graphitic in-plane Fe-N4 sites in a carbon matrix is energetically favorable over the formation of Fe-N2 sites. Chemisorption of ORR species O2, O, OH, OOH, and H2O and O-O bond breaking in peroxide occur on both Fe-N2 and Fe-N4 sites.

Catalytic activity of Co-N(x)/C electrocatalysts for oxygen reduction reaction: a density functional theory study.

First-principles DFT computations are performed to explain the origin and the mechanism of oxygen reduction reaction (ORR) on Co-N(x) (x = 2, 4) based self-assembled carbon supported electrocatalysts in alkaline and acidic media. The results show that the formation of graphitic Co-N(4) defect is energetically more favorable than the formation of graphitic Co-N(2) defect. Furthermore graphitic Co-N(4) defects are predicted to be stable at all potentials (U = 0-1.

Crystal structure of graphite under room-temperature compression and decompression.

Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C(4), H-, M-, R-, S-, W-, and Z-carbon).