Structural, electronic, and optical properties for the cubic, tetragonal, and monoclinic crystalline phases of ZrO 2 , as derived from ab initio full-relativistic calculations, are presented. The electronic structure calculations were carried out by means of the all-electron full potential linear augmented plane wave method, within the framework of the density functional theory and the local density approximation. The calculated carrier effective masses are shown to be highly anisotropic. The results obtained for the real and imaginary parts of the dielectric function, the reflectivity, and the refraction index, show good agreement with the available experimental results. In order to obtain the static dielectric constant of ZrO 2 , we added to the electronic part, the optical phonons contribution, which leads to values of ǫ 1 (0) ≃ 29.5, 26.2, 21.9, respectively along the xx, yy, and zz directions, for the monoclinic phase, in excellent accordance with experiment. Relativistic effects, including the spin-orbit interaction, are demonstrated to be important for a better evaluation of the effective mass values, and in the detailed structure of the frequency dependent complex dielectric function.

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We have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P2 1 /c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam one.

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Density functional calculations were performed to study the properties of the three main glycine solid-state polymorphs α, β, and γ and the glycine dihydrate (GDH) crystal. Optimized unit cell geometries, Kohn–Sham electron energy bands, electron densities of states, population charges, carrier effective masses, optical absorption, and complex dielectric functions were obtained for each glycine system using a GGA functional plus the TS dispersion correction, leading to lattice parameters very close to the experimental values. The theoretical fundamental gaps of all glycine crystals are indirect and near 5 eV. The carrier effective masses are anisotropic and especially heavy (∼26 free electron masses at most) for holes in the case of the GDH crystal. The optical absorption and the dielectric function are very sensitive to the polarization of light in all glycine-based crystals.

Using the density-functional theory, normconserving pseudopotenlials and plane-wave expansion$ we have calculated ab initio the equation of state and the principal phonon modes in boron phosphide, including their pressure dependence and the amplitude of the eigendisplacemenls. Good agreement with experiment is obtained, whenever a comparison is possible: in fact, most of the results are predictions. A tenparameter valence overlap Shell model is then mnslrucled from the available experimental dala, which are completed by the data obtained in the first-principle calculations: fm7snphonon ffequencies and eigenvectors The previous speculations about the anomalous behaviour of the effeclive charges are discussed in the conte~t of the present re5ults.

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We present, our preliminary results of a systematic theoretical study of the adsorption of N over As-terminated GaAs (100) (2×1) surfaces. We analyzed the changes in the bond-lengths, bond-angles and the energetics involved before and after deposition. Our results show that the N-atoms will prefer the unoccupied sites of the surface, close to the As dimer. The presence of N pushes the As dimer out of the surface, leading to the anion exchange between N and As atoms. Based on our results, we discussed the kinetics of the N islands formation during epitaxial growth of the III-Nitrides.