1,720,991 research outputs found
Si-atoms substitutions effects on the electronic and optical properties of coronene and ovalene
Full text linkWe report a computational comparative study of the ground and excited states properties of graphene nanoribbons, analyzing the case of coronene (C24H12) and ovalene (C32H14) and their silicon-atoms substituted counterparts with single, double and triple atomic insertions. We used density functional theory (DFT) and time-dependent DFT to quantify the effects on the electronic and optical properties as a result of the chemical modifications. In particular, we compared ground-state total energies, electron affinities, ionization energies, fundamental gaps and optical absorption spectra, between the original systems and each substituted one. For both the molecules, we observed a general reduction of the fundamental gap after chemical modification. Concerning the optical properties, therefore, we observed a redshift of the optical onset in all the cases; in particular, we have found that, in one ovalene and coronene trimer-substituted configuration, the absorption edge takes place in the IR
A computational study on the electronic and optical properties of boron-nitride circumacenes
No full textWe report a comparative and systematic computational analysis on the electronic and optical properties of the boron-nitride-made (BN) counterparts of the carbon-made circumacenes. Recently, these planar molecules have attracted interest for applications in the condensed matter physics domain. In particular, we focus on the five first members of this BN-family (from BN-coronene to BN-circumpentacene) presenting a comparison with their carbon analogues. For all the systems investigated, we calculate different electronic properties and the optical absorption spectra, performing all electron Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations. In the context of ab initio calculations we select a localized Gaussian basis-set matched with a hybrid exchange-correlation functional. We discuss possible implications of the observed BN cluster properties, which could be an alternative material or complementar as compared to their carbon analogues. In particular, concerning the optical properties, we have found that the main difference between the two families is that the BN molecules absorb in the UV, rather than in the visible as happens for the C-made parents. Moreover, we demonstrate that the electronic and optical observables of the BN clusters are nearly independent of the cluster size in contrast to what happens for their carbonaceous counterparts
Electronic and Optical properties of Hexathiapentacene within TD(DFT) schemes
No full textElectronic and Optical properties of Hexathiapentacene within TD(DFT) scheme
A computational investigation on the electronic and optical properties of Coronene and its Boron-Nitride and perfluorinated counterparts
Full text linkWe present a computational study on the electronic and optical properties of a representative C-made and Boron-Nitride-made (BN) planar molecule of interest for potential applications in the solid state domain. In particular, we analyzed the case of Coronene (C24H12) in its BN and perfluorinated analogues. We performed all electrons Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations using a localized Gaussian basis-set in combination with a hybrid exchange-correlation functional. For all the systems we have calculated different electronic properties and the optical absorption spectra. A discussion on the possible implications of the general trends, observed for the BN-made clusters properties as compared to their C-based parents, will be given
Computational investigation on the electronic, optical and transport properties of hexathiapentacene in the molecular and solid phases
No full textThe hexathiapentacene molecule (HTP), a derivative of pentacene (PNT) obtained by symmetric substitution of the six central hydrogens with sulfur atoms, has recently received increasing
attention for its potential applications in organic electronic devices. We present a Density Functional Theory (DFT) investigation of the electronic, optical and transport properties of HTP
molecule, in its molecular and solid phases. For the first part of the work we performed all-electron calculations using the hybrid exchange-correlation functional B3LYP in conjunction with a
Gaussian localized orbital basis set to expand the molecular orbitals. Electron affinities, ionization energies, fundamental energy-gaps, optical absorption spectra, exciton binding energies, and
reorganization energies for holes and electrons have been calculated and compared with the corresponding observables of PNT and with the available experimental data. Following sulfur
functionalization we found an increase of both ionization energies and electron affinities, a sensible reduction of the fundamental electronic gap, and a redshift of the optical absorption onset.
Notably, the intensity of the first absorption peak of HTP falling in the visible region is found to be nearly tripled with respect to the pure pentacene molecule. As to the corresponding HTP
molecular solid, we performed our simulations within a plane-wave+pseudopotential framework using the PBE exchange-correlation functional, with the inclusion of an empirical correction
taking into account dispersive interactions. The comparative analysis between the ground-state and excited-sate properties of solid-state HTP and PNT confirmed the general findings obtained
for the isolated molecules
Effects of perfluorination on the electronic, optical, and transport properties of polyaromatic hydrocarbons: pentaceneand pyrene in the molecular and solid phase
No full textWe report a comparative study on pentacene and pyrene polyaromatic
hydrocarbons (PAHs) and their perfluorinated counterparts. The study
has been performed for both the isolated molecule and their molecular
solid phases. The former are investigated, performing all-electron
calculations, using Density Functional Theory (DFT) and Time Dependent
DFT with localized gaussian basis set and hybrid B3LYP exchange
correlation functional, in order to quantify the effects of morphology
and chemical modifications on their electronic, optical, and
transport properties: in particular electron affinity, ionization energy,
fundamental gap, optical absorption, exciton binding energy, and reorganization
energies for holes and electrons. The molecular solids using
DFT-LDA with plane-waves basis set and ionic pseudopotentials in
order to determine and compare ground state properties. In contrast,
different exchange-correlation functionals (LDA, PBE0) are considered
HER2 heterogeneity in personalized therapy of gastro-oesophageal malignancies: An overview by different methodologies
No full textHuman epidermal growth factor receptor-2 (HER2)-expression gastro-oesophageal adenocarcinomas (GEA) gained interest as an important target for therapy with trastuzumab. In the current review, we focused the current knowledge on HER2 status in dysplastic and neoplastic gastric conditions, analyzing the methodological procedures to identify HER2 expression/amplification, as well as the proposed scoring recommendations. One of the most relevant questions to evaluate the useful impact of HER2 status on therapeutic choice in GEAs is represented by the significant heterogeneity of HER2 protein and gene expression that may affect the targeted treatment selection. Future development of biotechnology will continue to evolve in order to offer more powerful detection systems for the assessment of HER2 status. Finally, liquid biopsy as well as mutation/amplification of several additional genes may furnish an early detection of secondary HER2 resistance mechanisms in GEAs with a better monitoring of the treatment response
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mercapto-Benzamide Inhibitors effects on HIV NCp7 Protein: a parameter-free DFT based structural study
No full textThe action of the Mercapto-Benzamide (MB) class of molecules on the HIV
Nucleocapsid protein (HIV NCp7), a zinc finger protein, is an issue of relatively recent
research interest, relevant to develop a new class of effective and well tolerated HIV antivirals,
able to overcome virus escape strategies. MB molecules are easily and cheaply synthesized,
and show the ability to unfold the HIV Zinc-finger region, thus avoiding effective viral
replication. This effect is not still fully understood, and moreover is highly influenced by the
precise composition of MB aromatic ring and chain. Our approach to this biological problem is
to adopt a quantum parameter-free (ab-initio: AI) geometrical scheme based on density
functional theory (DFT) for the treatment of the electronic degrees of freedom to study with
atomistic resolution the action mechanism of MB molecules on NCp7. In particular with
respect to the role played by each MB functional group.We report and discuss the outcomes of
the here proposed DFT simulations with respect to the different final configurational structures
obtained.
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