A recently developed Floquet theory-based formalism for computing electron transport through a molecular bridge coupled to two metal electrodes in the presence of monochromatic ac radiation field is applied an experimentally relevant system, namely xylyl–dithiol molecule contact at either end with gold electrodes. In this treatment, nondissipative tight-binding model assumed describe conduction electric current. Net current wire calculated configurations electrode–wire–electrode system. one,...

In this work, we study the effect of a dual luminescence for CdSe quantum dots (QDs) doped by manganese impurity. effect, one line has fast relaxation and corresponds to light emission from conduction band, whereas second is very slow in with time 0.1–1.0 ms. The disappears diameters D ≥ 3.3 nm, therefore, becomes tunable QD size. problem computationally challenging because large size QDs high degeneracy energy states. To overcome problem, make four assumptions. These assumptions are...

This paper considers electron transport through a molecular bridge coupled to two metal electrodes in the presence of monochromatic radiation field. Current flow wire is calculated within nondissipative one-electron tight binding model quantum dynamics. Using Floquet theory, field-driven mapped an effective time-independent system characterized by tight-binding Hamiltonian with same essential structure as nondriven analog. Thus, Green’s Function methods for computing current wire, which have...

We study the effect of manganese impurities on optical and magnetic properties PbS quantum dots (QDs) different sizes. find that at low Mn concentrations, atoms slightly change absorption spectra pure nanocrystals. A soon as number increases a QD energy gap expands. In there is distinct exciton peak. With presence this peak smeared over almost disappears for larger concentrations. This indicates strong sp–d hybridization. also how an location inside can affect spectra. if are spread surface,...

Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress spintronics, holding great potential for future computing technologies. Here, we report a new approach leveraging tunneling current as tool controlling spin states CrI3. We reveal that can deterministically switch between spin-parallel and spin-antiparallel few-layer CrI3, depending on the polarity amplitude current. propose mechanism involving nonequilibrium accumulation graphene electrodes...

The nature of the chemical bonding a pentacene molecule to gold surface is studied. calculations are carried out using two very different methodologies, ab inito gaussian molecular orbital method and numerical atomic method, developed from well tested SIESTA approach. Using GAUSSIAN 09 package, we employ both local density B3LYP, long-range correlated functionals CAM-B3LYP, ωB97, ωB97X. For comparison, also calculate adsorption energy ATOMISTIX TOOLKIT with revised PBE functional. Within...

Scanning tunneling microscopy is utilized to investigate the local density of states a CH3NH3PbI3–xClx perovskite in cross-sectional geometry. Two electronic phases, 10–20 nm size, with different properties inside layer are observed by dI/dV mapping and point spectra. A power law dependence spectra revealed. In addition, distinct phases found have preferential orientations close normal direction film surface. Density functional theory calculations indicate that associated deviation I/Cl...

The quest for new materials with extraordinary electronic, magnetic, and optical properties leads to the synthesis of 2D nitrogenated microporous hole diameter 1.16 nm. We computationally study evolution energy bandgaps, optical, transport following substituents: hydrogen, fluorine, chlorine, iodine. find that such a small perturbation by these atoms has tremendous impact on electronic materials. Indeed, direct bandgaps can be tuned from 1.64 0.96 eV substituents hydrogen gaps demonstrate...

Room temperature ferromagnetic semiconductors have a great deal of advantage because their easy integration into semiconductor devices. ZnS nanocrystals (NCs), bulk, and surfaces exhibit d0 ferromagnetism at room temperature. The experiments reveal that NC takes place low temperatures only due to Zn vacancies (S do not contribute). To understand the mechanism ferromagnetism, we introduce surface-bulk model nanocrystal, which includes both surface bulk magnetizations. calculations demonstrate...

A huge enhancement in the incident photon-to-current efficiency of PbS quantum dot (QD) sensitized solar cells by manganese doping is observed. In presence Mn dopants with relatively small concentration (4 at. %), photoelectric current increases an average 300% (up to 700%). This effect cannot be explained light absorption mechanism because both experimental and theoretical spectra demonstrate several times decreases coefficient. To explain such dramatic increase photocurrent we propose...

We study new 3D materials, π-conjugated microporous polymers (aza-CMPs), where 2D layers are connected by methanoic and ethanoic acid groups. The crystal parameters the band structures calculated. energy gaps for a with (Eg3D=1.04eV) (Eg3D=1.26eV) connecting groups smaller than those material (Eg2D=1.64eV). symmetry of becomes lower aza-CMP changing selection rules optical spectra. upper hole bands become non-degenerate an doubly degenerate in valence zone more flat implying heavier masses...

We study d0 ferromagnetism in ZnS quantum dots (QDs) and nanowires (NW). To find the magnetization of medium large size nanocrystals (NC), we introduce surface-bulk (SB) model where separately calculated surface bulk contributions to total magnetic moment allow us for a nanocrystal (NC). For nanowire calculations accuracy SB varies from 0.2% 21% depending on Zn vacancy concentrations NC core. that higher concentration vacancies, larger nanocrystal. However, increases faster rather than...

Centrosymmetric skyrmions attract much attention from the research community because of their small sizes and high concentrations. These features can be useful for applications. Such are originated due to Ruderman-Kittel-Kasuya-Yosida Kondo interactions rather than Dzyaloshinski-Moria interaction. We study a topological Hall effect in such systems using Boltzmann equation nonequilibrium distribution function. For relaxation, we choose electron-acoustic phonon electron-skyrmion interactions....

In this work we study the electronic structure of CdmSem quantum dots various sizes and different shapes such as spheres cubes using DFT, TDDFT, CIS methods. This requires a careful computational analysis where proper exchange–correlation functional has to be chosen fit experimental optical gap. We find some differences in HOMO–LUMO gap values between cubes. general, gaps for have higher than those spheres. also calculate absorption spectra data energy levels oscillator strengths...

We find a large enhancement in the efficiency of CdSe quantum dot sensitized solar cells by doping with manganese. In presence Mn impurities relatively small concentrations (2.3%) photoelectric current increases up to 190%. The average photocurrent is about 160%. This effect cannot be explained light absorption mechanism because experimental and theoretical spectra demonstrate that there no change coefficient impurities. To explain such increase injection we propose tunneling electron from...

We study optical transitions in CdSe quantum dots doped by Mn atoms. At low concentrations the are spin-forbidden. Nevertheless, strong light absorption was experimentally found. To explain this effect we propose a new mechanism that includes two or more atoms closely placed to each other containing electrons with opposite spin projections. In case spin-flip is unnecessary. addition from different multiplicities. find strongest gap for an antiferromagnetic arrangement. The obtained results...

The concentration dependence of magnetic order Mn-doped CdSe nanocrystals is studied. distance between two Mn atoms imitates the dependence. To do more accurate calculations, we cut three fragments out a quantum dot and calculate ground state. We find that DFT calculations provide unreliable results where depends on chosen exchange correlation functional. Then, ab initio CASSCF method applied with multideterminant basis set. obtained indicate strong sp–d hybridization oscillations depending...

Topological semimetals possess nodal or nodal-line phases where conduction and valence bands touch at points lines in momentum space, respectively. Such band touching is symmetry protected gives rise to exotic interesting electronic properties. Coupling topological order with magnetism provides a platform for exploring time-reversal (TR) breaking physics, such as axion electrodynamics, inverse spin-galvanic effect, the quantized anomalous Hall effect. The Weyl semimetal (WSM) requires either...

Tunneling of two particles in synchronous and asynchronous regimes is studied the framework dissipative quantum tunneling. The critical temperature ${T}_{c}$ corresponding to a bifurcation underbarrier trajectory determined. effect heat bath local mode on probability two-dimensional tunneling transfer also investigated. At certain values parameters, degeneracy antiparallel trajectories important. Thus, 4, 6, 12, etc., pairs should be taken into account (a cascade bifurcations). For parallel...

In this work we study quantum dynamics of an electron transferred from a dot (QD) to semiconductor (SM) in quantum-dot-semiconductor solar cell. The proposed theoretical description includes the following interactions: electron-electron and electron-phonon interactions QD, interaction with light, SM, between electronic states QD SM tunneling approximation. light is considered dipole e-e important because transition takes place excitonic state; $e$-ph necessary describe relaxation state...

Dilute magnetic semiconductors (DMSs) are typically made by doping with transition metal elements. Compared to the well-understood bulk and thin film DMS, understanding of element effects in semiconducting quantum dots (QDs) is relatively poor. In particular, influence dopant locations rarely explored. Here, we present a comprehensive study Mn on electronic density states PbS QDs. Based results observed scanning tunneling microscopy, X-ray diffraction, electron paramagnetic resonance,...

Spin-spiral texture can substantially change charge transport properties in helimagnets. We find the anomalous Hall effect (AHE) exhibiting dramatic behavior with respect to chemical potential $\ensuremath{\mu}$ conical magnetic structures. The direct conductivity demonstrates kinks, and current exhibits minima maxima changing sign. analytically derive expression for energy bands eigenstates most general case. Because of potential, are split into two nonparabolic where lower band have one-...

A novel computational method for a surface Green’s function matrix is introduced the calculation of electrical current in molecular wires. The proposed nonrecursive approach includes an infinite number principal layers and yields second-order equation transformed matrix. solution found by direct diagonalization auxiliary without any iteration process. As soon as complex roots (≃ĜS) are calculated, gaps bands electronic structure found. It shown that determines spectral density matrix, is,...

Ab initio electron propagators in molecular systems with strong electron-electron and electron-phonon interactions are considered to study electronic properties. This research is important transfer reactions where the transition not any longer as a single process or temperature dependences of current-voltage characteristics wires aggregates. To calculate Green's functions, authors apply small polaron canonical transformation that intrinsically contains effects. According this transformation,...