L. V. C. Assali

Group IV graphene- and graphane-like nanosheets

We performed a first-principles investigation on the structural and electronic properties of group IV (C, SiC, Si, Ge, and Sn) graphene-like sheets in flat and buckled configurations and the respective hydrogenated or fluorinated graphane-like ones. The analysis on the energetics, associated with the formation of those structures, showed that fluorinated graphane-like sheets are very stable and should be easily synthesized in the laboratory. We also studied the changes of the properties of the graphene-like sheets as a result of hydrogenation or fluorination. The interatomic distances in those graphane-like sheets are consistent with the respective crystalline ones, a property that may facilitate integration of those sheets within three-dimensional nanodevices.

Stability and plasticity of silicon nanowires : The role of wire perimeter

We investigated the properties of stability and plasticity of silicon nanowires using molecular dynamics simulations. We considered nanowires with , and growth directions with several diameters and surface facet configurations. We found that the wire perimeter, and not the wire diameter, is the meaningful dimensional parameter. As a result, the surface facets play a central role on the nanowire energy, that follows a universal scaling law. Additionally, we have computed the response of a silicon nanowire to external load. The results were compared to available experimental and ab initio data.

Functionalized adamantane: Building blocks for nanostructure self-assembly

We report first principles calculations on the electronic and structural properties of chemically functionalized adamantane molecules, either in isolated or crystalline forms. Boron and nitrogen functionalized molecules, aza-, tetra-aza-, bora-, and tetra-bora-adamantane, were found to be very stable in terms of energetics, consistent with available experimental data. Additionally, a hypothetical molecular crystal in a zincblende structure, involving the pair tetra-bora-adamantane and tetra-aza-adamantane, was investigated. This molecular crystal presented a direct and large electronic bandgap and a bulk modulus of 20 GPa. The viability of using those functionalized molecules as fundamental building blocks for nanostructure self-assembly is discussed.

Hyperfine interactions in silicon quantum dots

We present an all-electron calculation of the hyperfine parameters for conduction electrons in Si, showing that: (i) all parameters scale linearly with the spin density at a

Isolated nickel impurities in diamond: A microscopic model for the electrically active centers

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Electronic properties and hyperfine fields of nickel-related complexes in diamond

Si site; (ii) the isotropic term is over 30 times larger than the anisotropic part; (iii) conduction electron charge density at a Si nucleus is consistent with experimental estimates; (iv) Overhauser fields in natural Si quantum dots (QDs) are two orders of magnitude smaller than in GaAs QDs. This reinforces the outstanding performance of Si in keeping spin coherence and opens access to reliable quantitative information aiming at spintronic applications.

Role of intrinsic defects in the electronic and optical properties of α-HgI2

We present a theoretical investigation on the structural and electronic properties of isolated nickel impurities in diamond. The atomic structures, symmetries, formation and transition energies, and hyperfine parameters of isolated interstitial and substitutional Ni were computed using ab initio total energy methods. Based on our results, we ultimately propose a consistent microscopic model which explains several experimentally identified nickel-related active centers in diamond.

First-principles studies of Ti impurities in SiC

We carried out a first principles investigation on the microscopic properties of nickel-related defect centers in diamond. Several configurations, involving substitutional and interstitial nickel impurities, have been considered either in isolated configurations or forming complexes with other defects, such as vacancies and boron and nitrogen dopants. The results, in terms of spin, symmetry, and hyperfine fields, were compared with the available experimental data on electrically active centers in synthetic diamond. Several microscopic models, previously proposed to explain those data, have been confirmed by this investigation, while some models could be discarded. We also provided new insights on the microscopic structure of several of those centers.

3 d transition metal impurities in diamond: Electronic properties and chemical trends

We investigated the role of intrinsic defects in the electronic and optical properties of mercuric iodide using ab initio methods. The calculations were performed using the total energy all electron methodology, considering full atomic relaxation. We computed the band structure, spin, formation and transition energies, and the dielectric function of isolated iodine and mercury vacancies in several charge states. Our results were compared to available experimental data on photoluminescence and photoplasticity in HgI2. We propose a microscopic model which can explain most of the data on those luminescent centers, unifying experimental results which suggested conflicting conclusions.

Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

Abstract In this work we perform a theoretical investigation on the atomic structure, atomic geometry, and formation energy of isolated substitutional and interstitial Ti impurities in cubic silicon carbide (3C–SiC), using the spin-polarized full-potential linearized augmented plane wave method. For each configuration, the atoms around the impurity site are allowed to relax without any constraints, following the damped Newton dynamics scheme. The overall structural stability is analyzed in the light of the electronic structure and the bonding features.