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    Calculation of electronic structure of a spherical quantum dot using a combination of quantum genetic algorithm and Hartree-Fock-Roothaan method
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2008) Cakir, Bekir; Oezmen, Ayhan; Atav, Uelfet; Yueksel, Hueseyin; Yakar, Yusuf
    The electronic structure of Quantum Dot (QD), GaAs/AlxGa1-xAs, has been investigated by using a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. One-electron system with an on-center impurity is considered by assuming a spherically symmetric confining potential of finite depth. The ground and excited state energies of one-electron QD were calculated depending on the dot radius and stoichiometric ratio. Expectation values of energy were determined by using the HFR method along with Slater-Type Orbitals (STOs) and QGA was used for the wave-functions optimization. In addition, the effect of the size of the basis set on the energy of QD was investigated. We also calculated the binding energy for a dot with finite confining potential. We found that the impurity binding energy increases for the finite potential well when the dot radius decreases. For the finite potential well, the binding energy reaches a peak value and then diminishes to a limiting value corresponding to the radius for which there are no bound states in the well. Whereas in previous study, in Ref. 40, for the infinite potential well, we found that the impurity binding energy increases as the dot radius decreases.
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    Computation of the oscillator strength and absorption coefficients for the intersubband transitions of the spherical quantum dot
    (ELSEVIER SCIENCE BV, 2009) Ozmen, Ayhan; Yakar, Yusuf; Cakir, Bekir; Atav, Uelfet
    The electronic structure and optical properties of one-electron Quantum Dot (QD) with and without an on-center impurity were investigated by assuming a spherically symmetric confining potential of finite depth. The energy eigenvalues and the state functions of QD were calculated by using a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothan (HFR) method. We have calculated the binding energy for the states 1s,1p,1d,1f, oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of the incident photon energy and incident optical intensity for the 1s-1p, 1p-1d and id-If transitions. The existence of the impurity has great influence on the optical absorption spectra and the oscillator strengths. Also we found that the magnitudes of the total absorption coefficients of the spherical QD increase for transitions between higher states. (C) 2009 Elsevier B.V. All rights reserved.
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    Investigation of electronic structure of a Quantum Dot using Slater-Type Orbitals and Quantum Genetic Algorithm
    (WORLD SCIENTIFIC PUBL CO PTE LTD, 2007) Cakir, Bekir; Ozmen, Ayhan; Atav, Uelfet; Yuksel, Hueseyin; Yakar, Yusuf
    In this study, electronic properties of a low-dimensional quantum mechanical structure have been investigated by using Genetic Algorithm (GA). One-and two-electron Quantum Dot (QD) systems with an on-center impurity are considerable by assuming the confining potential to be infinitely deep and spherically symmetric. Linear combinations of Slater-Type Orbitals (STOs) were used for the description of the single electron wave functions. The parameters of the wave function of the system were used as individuals in a generation, and the corresponding energy expectation values were used for objective functions. The energy expectation values were determined by using the Hartree-FockRoothaan (HFR) method. The orbital exponent zeta(i)'s and the expansion coefficient c(i)'s of the STOs were determined by genetic algorithm. The obtained results were compared with the exact result and found to be in a good agreement with the literature.
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    Theoretical investigation of intersubband nonlinear optical rectification in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells
    (WILEY-V C H VERLAG GMBH, 2007) Karabulut, Ibrahim; Atav, Uelfet; Safak, Haluk; Tomak, Mehmet
    In this study, a theoretical investigation of intersubband nonlinear optical rectification in Alx1Ga1-x1As/ GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells is presented. The electronic states in the asymmetric rectangular quantum well are described within the framework of the envelope function approach including the effects of band nonparabolicity and the effective mass mismatch. The nonlinear optical rectification is calculated using the density matrix formalism. It is found that the nonlinear optical rectification in the asymmetric rectangular quantum well depends sensitively on the parameters such as the width and the asymmetry of the potential well. The adjustable parameters allow for tuning of the asymmetric rectangular quantum well system to the desired wavelength while retaining a large optical rectification coefficient. This gives a new degree of freedom in various device applications based on nonlinear optical properties. Band nonparabolicity is found to significantly influence both electronic states and nonlinear optical rectification. Moreover the resulting optical rectification coefficient is much larger than the ones for bulk GaAs and some other theoretical studies in literature. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.