Juan E. Peralta

Energy band gaps and lattice parameters evaluated with the Heyd-Scuseria-Ernzerhof screened hybrid functional.

This work assesses the Heyd-Scuseria-Ernzerhof (HSE) screened Coulomb hybrid density functional for the prediction of lattice constants and band gaps using a set of 40 simple and binary semiconductors. An extensive analysis of both basis set and relativistic effects is given. Results are compared with established pure density functionals. For lattice constants, HSE outperforms local spin-density approximation (LSDA) with a mean absolute error (MAE) of 0.037 A for HSE vs 0.047 A for LSDA. For this specific test set, all pure functionals tested produce MAEs for band gaps of 1.0-1.3 eV, consistent with the very well-known fact that pure functionals severely underestimate this property. On the other hand, HSE yields a MAE smaller than 0.3 eV. Importantly, HSE correctly predicts semiconducting behavior in systems where pure functionals erroneously predict a metal, such as, for instance, Ge. The short-range nature of the exchange integrals involved in HSE calculations makes their computation notably faster than regular hybrid functionals. The current results, paired with earlier work, suggest that HSE is a fast and accurate alternative to established density functionals, especially for solid state calculations.

Enhanced half-metallicity in edge-oxidized zigzag graphene nanoribbons.

We present a comprehensive theoretical study of the electronic properties and relative stabilities of edge-oxidized zigzag graphene nanoribbons. The oxidation schemes considered include hydroxyl, lactone, ketone, and ether groups. Using screened exchange density functional theory, we show that these oxidized ribbons are more stable than hydrogen-terminated nanoribbons except for the case of the etheric groups. The stable oxidized configurations maintain a spin-polarized ground state with antiferromagnetic ordering localized at the edges, similar to the fully hydrogenated counterparts. More important, edge oxidation is found to lower the onset electric field required to induce half-metallic behavior and extend the overall field range at which the systems remain half-metallic. Once the half-metallic state is reached, further increase of the external electric field intensity produces a rapid decrease in the spin magnetization up to a point where the magnetization is quenched completely. Finally, we find that oxygen-containing edge groups have a minor effect on the energy difference between the antiferromagnetic ground state and the above-lying ferromagnetic state.

Magnetic Boron Nitride Nanoribbons with Tunable Electronic Properties

We present theoretical evidence, based on total-energy first-principles calculations, of the existence of spin-polarized states well localized at and extended along the edges of bare zigzag boron nitride nanoribbons. Our calculations predict that all the magnetic configurations studied in this work are thermally accessible at room temperature and present an energy gap. In particular, we show that the high spin state, with a magnetic moment of 1 muB at each edge atom, presents a rich spectrum of electronic behaviors as it can be controlled by applying an external electric field in order to obtain metallic <--> semiconducting <--> half-metallic transitions.

Basis set dependence of NMR spin–spin couplings in density functional theory calculations: first row and hydrogen atoms

Abstract We analyze the basis set dependence of NMR spin–spin coupling constants calculated using density functional theory in a set of benchmark molecules containing first row and hydrogen atoms. We find that similarly to calculations based on wavefunction theory, the flexibility of core gaussian basis functions plays a key role. For the set of molecules under consideration, we have analyzed the basis set limit and studied basis set of triple-ζ quality, which may be useful for practical applications.

Edge effects in finite elongated graphene nanoribbons

We analyze the relevance of finite-size effects to the electronic structure of long graphene nanoribbons using a divide and conquer density functional approach. We find that for hydrogen terminated graphene nanoribbons, most of the physical features appearing in the density of states of an infinite graphene nanoribbon are recovered at a length of

Advances in Theoretical and Physical Aspects of Spin–Spin Coupling Constants

40\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Accurate prediction of the electronic properties of low-dimensional graphene derivatives using a screened hybrid density functional.

. Nevertheless, even for the longest systems considered (

Lithium adsorption on zigzag graphene nanoribbons

72\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Screened exchange hybrid density-functional study of the work function of pristine and doped single-walled carbon nanotubes

long) pronounced edge effects appear in the vicinity of the Fermi energy. The weight of these edge states scales inversely with the length of the ribbon, and they are expected to become negligible only at ribbon lengths of the order of micrometers. Our results indicate that careful consideration of finite-size and edge effects should be applied when designing new nanoelectronic devices based on graphene nanoribbons. These conclusions are expected to hold for other one-dimensional systems such as carbon nanotubes, conducting polymers, and DNA molecules.

Density functional investigations of the properties and thermochemistry of UF6 and UF5 using valence-electron and all-electron approaches

Publisher Summary This chapter discusses advances in the theoretical and physical aspects of spin–spin coupling constants. From both theoretical and experimental points of view, the analysis of high-resolution NMR parameters is an important problem, and its significance for the understanding of molecular electronic structure can hardly be stressed enough. When both approaches are taken together, an excellent example of the Born–Opperheimer approximation is obtained because experimentalists measure transitions among nuclear states that are modified by the interactions among magnetic nuclei, external magnetic field, and electrons, while theoreticians study the way the electronic wave function is modified owing to those interactions. The empirical Hamiltonian describes the way nuclear spin energy levels are modified both by the static magnetic field provided by a spectrometer and by the interactions between magnetic nuclei and electrons belonging to a given molecule.