Accuracy of dielectric-dependent hybrid functionals in the prediction of optoelectronic properties of metal oxide semiconductors: a comprehensive comparison with many-body GW and experiments.

Understanding the electronic structure of metal oxide semiconductors is crucial to their numerous technological applications, such as photoelectrochemical water splitting and solar cells. The needed experimental and theoretical knowledge goes beyond that of pristine bulk crystals, and must include the effects of surfaces and interfaces, as well as those due to the presence of intrinsic defects (e.g. oxygen vacancies), or dopants for band engineering. In this review, we present an account of the recent efforts in predicting and understanding the optoelectronic properties of oxides using ab initio theoretical methods. In particular, we discuss the performance of recently developed dielectric-dependent hybrid functionals, providing a comparison against the results of many-body GW calculations, including G 0 W 0 as well as more refined approaches, such as quasiparticle self-consistent GW. We summarize results in the recent literature for the band gap, the band level alignment at surfaces, and optical transition energies in defective oxides, including wide gap oxide semiconductors and transition metal oxides. Correlated transition metal oxides are also discussed. For each method, we describe successes and drawbacks, emphasizing the challenges faced by the development of improved theoretical approaches. The theoretical section is preceded by a critical overview of the main experimental techniques needed to characterize the optoelectronic properties of semiconductors, including absorption and reflection spectroscopy, photoemission, and scanning tunneling spectroscopy (STS).

Conformational dependence of the circular dichroism spectra of single amino acids from plane-waves-based density functional theory calculations.

We study the conformational dependence of circular dichroism (CD) spectra of amino acid molecules by means of an efficient ab initio DFT approach which is free from the typical gauge invariance issues arising with the use of localized basis sets and/or real-space grids. We analyze the dependence of the chiroptical spectra on the backbone dihedrals in the specific case of alanine and consider the role of side chain degrees of freedom at the examples of leucine, phenylalanine, and serine, whose side chains have different physicochemical properties. The results allow one to identify the most diagnostic regions of the CD spectra and to critically compare the conformations which match the experimental CD data with conformations extracted from the rotamer library. The inclusion of a solvation shell of explicit water molecules and its effect on the CD spectrum are analyzed at the example of alanine.

Oxidation of carbynes: signatures in infrared spectra.

We report and solidly interpret the infrared spectrum of both pristine and oxidized carbynes embedded in a pure-carbon matrix. The spectra probe separately the effects of oxidation on sp- and on sp(2)-hybridized carbon, and provide information on the stability of the different structures in an oxidizing atmosphere. The final products are mostly short end-oxidized carbynes anchored with a double bond to sp(2) fragments, plus an oxidized sp(2) amorphous matrix. Our results have important implications for the realization of carbyne-based nano-electronics devices and highlight the active participation of carbynes in astrochemical reactions where they act as carbon source for the promotion of more complex organic species.

Double excitations in finite systems.

Time-dependent density-functional theory (TDDFT) is widely used in the study of linear response properties of finite systems. However, there are difficulties in properly describing excited states, which have double- and higher-excitation characters, which are particularly important in molecules with an open-shell ground state. These states would be described if the exact TDDFT kernel were used; however, within the adiabatic approximation to the exchange-correlation (xc) kernel, the calculated excitation energies have a strict single-excitation character and are fewer than the real ones. A frequency-dependent xc kernel could create extra poles in the response function, which would describe states with a multiple-excitation character. We introduce a frequency-dependent xc kernel, which can reproduce, within TDDFT, double excitations in finite systems. In order to achieve this, we use the Bethe-Salpeter equation with a dynamically screened Coulomb interaction W(omega), which can describe these excitations, and from this we obtain the xc kernel. Using a two-electron model system, we show that the frequency dependence of W does indeed introduce the double excitations that are instead absent in any static approximation of the electron-hole screening.

First-principles study of silicon nanocrystals: structural and electronic properties, absorption, emission, and doping.

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nanostructures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si--O--Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.

[Blue nevus of the uterine cervix: description of a case and review of the literature]. / Il nevo blu della cervice uterina: descrizione di un caso e revisione della letteratura.

Blue nevus is a pigmented lesion of dermal melanocytes; the extracutaneous locations are uncommon. We report a case of a blue nevus of the uterine cervix in a 53 years old woman, with histochemical and immunohistochemical investigations.

Structural and optical properties of the Ge(111)-(2 x 1) surface.

We study the two lowest-energy isomers of the Ge(111)-(2 x 1) surface, by a state-of-the-art first-principles calculation of their optical spectra, including the electron-hole interaction effects. A comparison of our results with the available experimental data suggests that, at difference with the silicon case, the stablest isomer differs from the standard "buckled Pandey chains" reconstruction. This conclusion is supported by accurate total-energy results.

Neuron-specific enolase (gamma enolase, gamma-gamma dimer) expression in Hodgkin's disease and large cell lymphomas.

BACKGROUND: The presence of gamma-enolase, gamma gamma dimer, or neuron-specific enolase (NSE) has been demonstrated in miscellaneous tumors, including malignant lymphomas. Up to now these results have been interpreted as non-specific, although NSE can be expressed by normal B and T lymphoid cells at a particular stage of differentiation. The aim of the present study was to investigate the expression of NSE in a large series of malignant lymphomas, including Hodgkin's disease, in relation to morphology and immunophenotype. MATERIALS AND METHODS: Frozen and paraffin embedded sections from 16 cases of Hodgkin's disease (4 lymphocyte predominance, nodular; 4 mixed cellularity; 6 nodular sclerosis; 2 lymphocyte depletion) and 35 cases of non-Hodgkin's lymphomas were investigated in order to evaluate the expression of NSE, its specificity and correlation to immunophenotype or other immunological cell markers. Among the non-Hodgkin's lymphomas, there were 9 Anaplastic Large Cell (CD30+) Lymphomas; 2 Peripheral Large T-Cell Lymphomas; 22 Diffuse Large B-Cell Lymphomas and 2 Primary Mediastinal Large B-Cell Lymphomas. RESULTS: In Hodgkin's disease, NSE showed a diffuse cytoplasmic reaction in CD30+ Reed-Sternberg cells, whereas the "popcorn" (L&H) cells of lymphocyte predominance, nodular variant cases, were always negative. Among the non-Hodgkin's lymphomas, NSE positivity was found only in lymphomas expressing CD30. All the other cases were negative. No relationship was found between NSE and B- or T-immunophenotype. CONCLUSIONS: Our results suggest that a link between NSE and CD30 expression exists in malignant lymphomas. However, at the moment this has not been sufficiently investigated and is subject to speculation.