We have performed density-functional calculations for III-V nitrides using the pseudopotential plane-wave method where the d states of the Ga and In atoms are included as valence states. Results obtained using both the local-density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional are compared. Bulk properties, including lattice constants, bulk moduli and derivatives, cohesive energies, and band structures are reported for AlN, GaN, and InN in zinc-blende and wurtzite structures. We also report calculations for some of the bulk phases of the constituent elements. The performance of our pseudopotentials and various convergence tests are discussed. We find that the GGA yields improved physical properties for bulk Al, ${\mathrm{N}}_2,$ and bulk AlN compared to the LDA. For GaN and InN, essentially no improvement is found: the LDA exhibits overbinding, but the GGA shows a tendency for underbinding. The degree of underbinding and the overestimate of the lattice constant as obtained within the GGA increases on going from GaN to InN. Band structures are found to be very similar within the LDA and GGA. For the III-V nitrides, the GGA therefore does not offer any significant advantages; in particular, no improvement is found with respect to the band-gap problem.

The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, first-principles density-functional theory calculations using the full-potential linearized augmented plane wave (FLAPW) method within the local-density approximation (LDA) and with the generalized gradient approximation (GGA) have been performed. We investigate the bulk electronic and physical properties of a series of early transition metal mononitrides, namely, those formed with 3d metals (ScN, TiN, VN), 4d metals (YN, ZrN, NbN), and 5d metals (LaN, HfN, TaN) in the rocksalt structure. In particular, lattice constants, bulk moduli, heats of formation, and cohesive energies as well as bulk band structures and densities of states are reported, and trends discussed. We find that the GGA yields 1%–2% larger lattice constants, 10%–20% smaller bulk moduli, and 10%–30% lower heats of formation compared to the LDA. The GGA slightly overestimates lattice constants, but leads overall to an improved agreement with experiment compared to the LDA, for which the values are too small. These materials are metallic with the exception of ScN, YN, and LaN, which appear to be semimetals within the LDA (and GGA), but are in fact semiconductors with indirect band gaps of 1.58, 0.85, and 0.75 eV, respectively, as revealed by calculations performed using the screened-exchange LDA approach. These last, relatively unexplored, refractory III-V nitrides may therefore have potential use in device applications; in particular, ScN is well lattice matched to GaN, a wide-band-gap semiconductor that is of great current interest in relation to optoelectronic devices, and high temperature and high power electronic applications.

Heating of a ruthenium surface on which carbon monoxide and atomic oxygen are coadsorbed leads exclusively to desorption of carbon monoxide. In contrast, excitation with femtosecond infrared laser pulses enables also the formation of carbon dioxide. The desorption is caused by coupling of the adsorbate to the phonon bath of the ruthenium substrate, whereas the oxidation reaction is initiated by hot substrate electrons, as evidenced by the observed subpicosecond reaction dynamics and density functional calculations. The presence of this laser-induced reaction pathway allows elucidation of the microscopic mechanism and the dynamics of the carbon monoxide oxidation reaction.

Basal-plane stacking faults in wurtzite AlN, GaN, and InN are studied using density-functional-pseudopotential calculations. The formation energies follow the trend exhibited for the zinc-blende/wurtzite energy differences in the bulk materials, namely, lowest energy for GaN and highest for AlN. Type-I stacking faults have the lowest energy, followed by type-II stacking faults, and finally extrinsic stacking faults. We also examine a type of intrinsic stacking fault that has not, to the best of our knowledge, been previously discussed; its energy is slightly lower than the type-II faults. Investigations of the electronic structure reveal that there are no localized states in the band gap. However, stacking faults can bound a quantum-well-like region of zinc-blende material surrounded by the wurtzite host, giving rise to a luminescence line below the wurtzite band gap.

To obtain insight into the structure and surface stoichiometry of copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we perform density-functional theory calculations to investigate the relative stability of low-index copper oxide surfaces. By employing the technique of “ab initio atomistic thermodynamics,” we identify low-energy surface structures that are most stable under realistic catalytic conditions are found to exhibit a metallic character. Three surfaces are shown to have notably lower surface free energies compared to the others considered and could be catalytically relevant; in particular, under oxygen-rich conditions, they are the ${\mathrm{Cu}}_2\mathrm{O}\left(110\right):\mathrm{Cu}\mathrm{O}$ surface, which is terminated with both Cu and O surface atoms, and the ${\mathrm{Cu}}_2\mathrm{O}\left(111\right)\text{−}{\mathrm{Cu}}_{\mathrm{CUS}}$ surface, which contains a surface (coordinatively unsaturated) Cu vacancy, while for the oxygen-lean conditions, the ${\mathrm{Cu}}_2\mathrm{O}\left(111\right)$ surface with a surface interstitial Cu atom is found to be energetically most favorable, highlighting the importance of defects at the surface.

Hexagonal boron nitride (hBN) has recently emerged as a fascinating platform for room-temperature quantum photonics due to the discovery of robust visible light single-photon emitters. In order to utilize these emitters, it is necessary to have a clear understanding of their atomic structure and the associated excitation processes that give rise to this single photon emission. Here, we performed density-functional theory (DFT) and constrained DFT calculations for a range of hBN point defects in order to identify potential emission candidates. By applying a number of criteria on the electronic structure of the ground state and the atomic structure of the excited states of the considered defects, and then calculating the Huang–Rhys (HR) factor, we found that the C_BV_N defect, in which a carbon atom substitutes a boron atom and the opposite nitrogen atom is removed, is a potential emission source with a HR factor of 1.66, in good agreement with the experimental HR factor. We calculated the photoluminescence (PL) line shape for this defect and found that it reproduces a number of key features in the experimental PL lineshape.