W.V.M. Machado

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.

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

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.

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

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.

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

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.

First-principles studies of Ti impurities in SiC

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.

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

First principles calculations have been used to investigate the trends on the properties of isolated 3

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

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Manganese impurities in boron nitride

transition metal impurities (from Sc to Cu) in diamond. Those impurities have small formation energies in the substitutional or double semivacancy sites and large energies in the interstitial site. Going from Sc to Cu, the 3

Structural, electronic, and vibrational properties of amino-adamantane and rimantadine isomers.

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Crystal engineering using functionalized adamantane

-related energy levels in the band gap move from the top of the band gap toward the valence band in all three sites. Trends in electronic properties and transition energies of the impurities, in the substitutional or interstitial sites, are well described by a simple microscopic model considering the electronic occupation of the 3