Whereas the conventional practice of referring binding energies deep donors and acceptors to band edges host semiconductor does not produce transparent chemical trends when same impurity is compared in different crystals, them vacuum level through use photothreshold reveals a remarkable material invariance levels III-V II-VI semiconductors. It shown that this consequence antibonding nature gap with respect atom-host orbital combinations.

The excitation energies of impurities in semiconductors, as well their donor and acceptor ionization energies, represent a combination one-electron many-electron multiplet effects, where the latter contribution becomes increasingly significant localized states are formed. Analysis absorption data for $3d$ is often obscured by inability contemporary theories (e.g., Tanabe-Sugano approach) to separate these two contributions inadequacy mean-field, that neglect effects altogether. We present...

We perform ab initio calculations of optical properties for a typical semiconductor conjugated polymer, poly-para-phenylenevinylene, in both isolated chain and crystalline packing. In order to obtain results excitonic energies real-space wave functions we explicitly include electron-hole interaction within the density-matrix formalism. find that details arrangement crucially affect properties, leading richer exciton structure opening nonradiative decay channels. This has implications...

Magnetic properties of a single vacancy in graphene is relevant and still much discussed problem. The experimental results point to clearly detectable magnetic defect state at the Fermi energy, while calculations based on density functional theory (DFT) yield widely varying for moment, range $\ensuremath{\mu}=1.04--2.0\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$. We present multitool ab initio theoretical study same defect, using two simulation protocols crystal (cluster periodic...

We present the first theoretical calculations of electronic structure long (200 rings) linear chains polyaniline, ranging in composition from leucoemeraldine to emeraldine, allowing for compositional disorder that sequence quinoid-benzenoid groups is random. show random protonation disordered polymers may induce p-type conductivity: This process pulls Fermi energy down into valence band, past localized band tails, extended states. The effect only seen if taken account.

The electronic structure of Cu, Ag, and Au impurities in silicon is studied self-consistently using the quasiband crystal-field Green's-function method. We find that a substitutional model results two-level (acceptor donor), three-charge-state (${A}^{+}$, ${A}^{0}$, ${A}^{\mathrm{\ensuremath{-}}}$) system, which suggests these defects are amphoteric. Our show form e-type ${t}_{2}$-type resonances (CFR) near center valence band dangling-bond hybrid (DBH) ${t}_{2}$ level gap....

The effects of edge covalent functionalization on the structural, electronic, and optical properties elongated armchair graphene nanoflakes (AGNFs) are analyzed in detail for a wide range terminations, within framework Hartree–Fock-based semiempirical methods. chemical features functional groups, their distribution, resulting system symmetry identified as key factors that determine modification strutural optoelectronic features. While electronic gap is always reduced presence substituents,...

We report the inclusion of electron-electron correlation in calculation transport properties within an ab initio scheme. A key step is reformulation Landauer's approach terms effective transmittance for interacting electron system. apply this framework to analyze effect short-range interactions on Pt atomic wires and discuss coherent incoherent correction mean-field approach.

We investigate the optical properties of edge-functionalized graphene nanosystems, focusing on formation junctions and charge-transfer excitons. consider a class structures that combine main electronic features with wide tunability large polycyclic aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we show that, upon convenient choice functional groups, low-energy excitations remarkable character oscillator strength are obtained. These can be further modulated through...

The optical excitations of elongated graphene nanoflakes finite length are investigated theoretically through quantum chemistry semiempirical approaches. spectra and the resulting dipole fields analyzed, accounting in full atomistic details for confinement effects, which crucial nanoscale regime. We find that these nanostructures dominated at low energy by with strong intensity, comprised characteristic coherent combinations a few single-particle transitions comparable weight. They give rise...

We present a theoretical study of the transport parameters in prototype conjugated-polymer, poly-para-phenylenevinylene, two different possible crystalline packings. Our analysis is performed through density-functional electronic structure calculations, and allows one to obtain fundamental describing charge transport. The transfer integrals are found be crucial quantity appreciate effects aggregation on conduction properties: our results indicate that interchain interactions can viewed as...

A Schiff base type polymer containing phenanthrene and an aliphatic spacer in the main chain was prepared, its photophysical behavior diluted concentrated solutions as well film form studied by steady-state fluorescence spectroscopy. These data indicated that ground-state fluorescent aggregates were present films. Time-resolved measurements conditions showed biexponential decay implying different microenvironments around chromophore. Theoretical simulations predicted aggregation π-stack...

We present for the first time a study of finite and infinite polymers 5,6-indolequinone. show that band structure polymer presents semiconductor characteristics, intrinsic paramagnetism eumelanin can be modeled through electron trapping at deep ‘‘end-effect’’ defects.

We report ab initio calculations of total energies and electronic structures P, As, Sb donors in GaAs InP. In the ${\mathit{T}}_{\mathit{d}}$ geometry, all these defects exhibit two donor states forbidden gap: an internal optical excitation energy order 1 eV, a Franck-Condon shift 0.1 eV. All possess metastable geometry electrically neutral vacancy-interstitial pair with no band gap. discuss differences between six systems explain why optically inducible transition to state is inefficient...

We present a new multiplet theory that separates mean-field from effects in the excitation and donor-acceptor ionization spectra of localized impurities. Analysis experimental data for all $3d$ impurities ZnO, ZnS, ZnSe, GaP which sufficient exist bulk Mott insulators CoO, MnO, NiO reveals, first time, regular chemical trends many-electron with impurity host-crystal covalency delineates regime where one-electron is applicable region it not.

We investigated theoretically the effect of covalent edge functionalization, with organic functional groups, on electronic properties graphene nanostructures and nanojunctions. Our analysis shows that functionalization can be designed to tune electron affinities ionization potentials flakes, control energy alignment frontier orbitals in nanometer-wide junctions. The stability proposed mechanism is discussed respect their number as well width nanostructures. results our work indicate...

We follow the evolution of ionization potential (IP) for paradigmatic quasi-one-dimensional transacetylene family conjugated molecules, from short to long oligomers and infinite polymer transpolyacetylene (TPA). Our results are very close experimental available data. find that IP varies with oligomer length converges given value TPA a smooth, coupled inverse-length-exponential behavior. prediction is based on an ``internally consistent'' scheme adjust exchange mixing parameter...

The crystal-induced energy splitting of the lowest excitonic state in polymer crystals, so-called Davydov Δ, is calculated with a first-principles density-matrix scheme. We show that different crystalline arrangements lead to significant variations from below above thermal kBT at room temperature, relevant implications on luminescence efficiency. This one more piece evidence supporting fact control interchain interactions and solid-state packing essential for design efficient optical devices.

Dopant atoms can segregate to ${\mathrm{SiO}}_{2}/\mathrm{Si}(001)$ interfaces and be deactivated there. Using phosphorus as a typical example of donor guided by results ab initio calculations, we present model segregation. We find that P is trapped at the interface in form threefold-coordinated atoms. The atomic detailed configuration process incorporation depend on concentration ${C}_{\mathrm{P}}$ vicinity interface. At low ${C}_{\mathrm{P}},$ prefer substitute Si with dangling bonds. high...

We investigate the electronic structure of ideal ordered polymers 5,6-indolequinone, in one or other redox form. These molecules are most abundant constituents eumelanin, pigment appearing human skin. Our study is carried out through Hückel π-electron theory, which allows us to follow trends from a single monomer—the isolated molecules—to finite up 10 units, and infinite polymers. have chosen different polymerization directions produce semiconducting chains. The comparison between very...

We have study by means of DFT+U and thermodynamic calculations the doping response p‐type transparent oxide NiO. found from calculated defect formation enthalpies that Ni vacancy, not O interstitial, is main source nonstoichiometry in On other hand, free‐hole concentration at room temperature pure NiO remains very low compared to vacancies; this due too large ionization energy vacancy. The can be strongly increased extrinsic dopants with a more shallow donor as it illustrated for case Li.

Thermally activated delayed fluorescence has been found in a group of tricarbazolylamines that are purely electron-donating, non-charge-transfer (CT) molecules. We show the reverse intersystem crossing step these materials is mediated through upper triplet states. Reverse internal conversion shown to be thermally mechanism behind harvesting mechanism. The strongly mixed n−π*/π–π* character lowest energy optical transitions retains high oscillator strength and gives rise ΦPL. Organic...

The electronic and optical properties of polycyclic aromatic hydrocarbons (PAHs) present a strong dependence on their size geometry. We tackle this issue by analyzing the spectral features two prototypical classes PAHs, belonging to D6h D2h symmetry point groups related coronene as multifunctional seed. While variation induces an overall red shift spectra redistribution oscillator strength between main peaks, lower molecular is responsible for appearance new features. Along with broken...