Constantinos Simserides

Electronic parameters for charge transfer along DNA

Abstract.We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The

Local absorption spectra of artificial atoms and molecules

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Intrinsic optical bistability in a two-subband system in a semiconductor quantum well: Analytical results

molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wave functions and energies of DNA bases are discussed and then used for calculating the corresponding wave functions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the

Linear and nonlinear optical properties of a two-subband system in a symmetric semiconductor quantum well

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Control of intersubband quantum well transitions with chirped electromagnetic pulses

molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons. Our findings are also compared with existing calculations from first principles.

Empirical LCAO parameters for π molecular orbitals in planar organic molecules

We investigate theoretically the spatial dependence of the linear absorption spectra of single and coupled semiconductor quantum dots, where the strong three-dimensional quantum confinement leads to an overall enhancement of Coulomb interaction and, in turn, to a pronounced renormalization of the excitonic properties. We show that\char22{}because of such Coulomb correlations and the spatial interference of the exciton wave functions\char22{}unexpected spectral features appear whose intensity depends on spatial resolution in a highly nonmonotonic way when the spatial resolution is comparable with the excitonic Bohr radius. We finally discuss how the optical near-field properties of double quantum dots are affected by their coupling.

Effects of the task of categorizing FM direction on auditory evoked magnetic fields in the human auditory cortex

We study theoretically the conditions under which optical bistability is achievable in a two-subband system in a semiconductor quantum well. We consider the interaction of the two-subband system with a continuous wave electromagnetic field, which induces intersubband transitions. For the description of the system dynamics we use the effective nonlinear density matrix equations. We solve these equations analytically, in the steady state, for a GaAs/AlGaAs quantum well structure. For several combinations of the values of the parameters three real solutions of the population inversion arise and the phenomenon of optical bistability prevails.

Near-Field Optical Properties of Quantum Dots, Applications and Perspectives

We study the linear and nonlinear optical response of intersubband transitions in a semiconductor quantum well. We describe the coupling of the quantum well structure with the electromagnetic field by using the nonlinear density matrix equations, in the two-subband approximation. We provide proper approximate analytical solutions to these equations that are used for the closed-form determination of the optical susceptibilities χ(1), χ(3), and χ(5). We also explore the dependence of χ(1), χ(3), and χ(5) on the electron sheet density for a specific double GaAs/AlGaAs quantum well.

Optical Spectra of Single Quantum Dots: Influence of Impurities and Few-Particle Effects

We study the interaction of chirped electromagnetic pulses with intersubband transitions of a double semiconductor quantum well. We consider the ground and first excited subbands and give emphasis to controlled intersubband population transfer. The system dynamics is described by the nonlinear density matrix equations that include the effects of electron-electron interactions. These equations are solved numerically for various values of the electron sheet density for a realistic double GaAs/AlGaAs quantum well, and the efficiency of population transfer is discussed.

Unbiased charge oscillations in B-DNA: monomer polymers and dimer polymers.

A novel parametrization within a simplified LCAO model (a type of Hückel model) is presented for the description of π molecular orbitals in organic molecules containing π-bonds between carbon, nitrogen, or oxygen atoms with sp2 hybridization. It is shown that the model is quite accurate in predicting the energy of the highest occupied π orbital and the first π–π* transition energy for a large set of organic compounds. Four empirical parameter values are provided for the diagonal matrix elements of the LCAO description, corresponding to atoms of carbon, nitrogen with one pz electron, nitrogen with two pz electrons, and oxygen. The bond-length dependent formula of Harrison (proportional to 1/d 2) is used for the non-diagonal matrix elements between neighbouring atoms. The predictions of our calculations have been tested against available experimental results in more than sixty organic molecules, including benzene and its derivatives, polyacenes, aromatic hydrocarbons of various geometries, polyenes, ketones, aldehydes, azabenzenes, nucleic acid bases and others. The comparison is rather successful, taking into account the small number of parameters and the simplicity of the LCAO method, involving only pz atomic-like orbitals, which leads even to analytical calculations in some cases.