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Öğe 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, YusufThe 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.Öğe Calculation of hyperfine interaction in spherical quantum dot(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2015) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, we have calculated the unperturbed wavefunctions and energy eigenvalues of the ground and excited states of a spherical quantum dot, GaAs/AlxGa1-xAs, by using quantum genetic algorithm and Hartree-Fock Roothaan method. Hyperfine coupling constant and hyperfine energy of is, 2p, 3d and 4f levels are carried out as a function of dot radius. The results show that the hyperfine constant and hyperfine energy varies rapidly in the strong and medium confining regions as dot radius decreases. It is worth pointing out that dot radius, impurity charge and angular momentum have a strong influence on the hyperfine energy. It is also found that hyperfine energy and hyperfine splitting vary with aluminium concentration ratio x. (C) 2015 Elsevier Ltd. All rights reserved.Öğe Calculation of oscillator strength. and the effects of electric field on energy states, static and dynamic polarizabilities of the confined hydrogen atom(ELSEVIER, 2014) Cakir, Bekir; Yakar, Yusuf; Ozmen, AyhanIn this study, we investigate the effect of an electric field on energy states of a spherical quantum dot with infinite confining potential using the perturbation method. We also perform the static dipole and dynamic dipole polarizabilities. In addition, the oscillator strengths have been calculated for the dipole transitions between higher unperturbed states. The results show that impurity and dot radius have an important effect on the Stark shift, and the effect of electric field is insensitive in small dot radii. For the excited states the Stark shift from the first-order increases linearly with the increase of electric field strength. On the other hand, the Stark shift from the first-order decreases with increasing of the magnetic quantum number. A very important future is that, for dot radius region 1.8 a(B) <= R <= 7a(B), the static dipole polarizabilities change very quickly. In addition, it is found that as the dot radius increases, the photon energy corresponding to the singularity of dynamic dipole polarizability decreases. (C) 2013 Elsevier B.V. All rights reserved.Öğe Calculation of Zeeman splitting and Zeeman transition energies of spherical quantum dot in uniform magnetic field(ELSEVIER SCIENCE BV, 2016) Cakir, Bekir; Atav, Ufet; Yakar, Yusuf; Ozmen, AyhanIn this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s-, 2p-, 3d- and 4f-energy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s-, 2p-, 3d- and 4f-energy states. We also have calculated the Zeeman transition energies between 2p -> 1s and 3d -> 2p states with m = 0, +/- 1 and 0, +/- 1, +/- 2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions. (C) 2016 Elsevier B.V. All rights reserved.Öğe Computation of hyperfine energies of hydrogen, deuterium and tritium quantum dots(ELSEVIER SCIENCE BV, 2016) Cakir, Bekir; Ozmen, Ayhan; Yakar, YusufThe hyperfine energies and hyperfine constants of the ground and excited states of hydrogen, deuterium and tritium quantum dots(QDs) are calculated. Quantum genetic algorithm (QGA) and Hartree-Fock-Roothaan (HFR) methods are employed to calculate the unperturbed wave functions and energy eigenvalues. The results show that in the medium and strong confinement regions the hyperfine energy and hyperfine constant are strongly affected by dot radius, impurity charge, electron spin orientation, impurity spin and impurity magnetic moment. Besides, in all dot radii, the hyperfine splitting and hyperfine constant of the confined hydrogen and tritium atoms are approximately equivalent to each other and they are greater than the confined deuterium atom. (C) 2015 Elsevier B.V. All rights reserved.Öğe Computation of Ionization and Various Excited State Energies of Helium and Helium-Like Quantum Dots(WILEY-BLACKWELL, 2011) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn the effective mass approximation, we calculated the wave functions and some energy states of helium and helium-like quantum dots (QDs) with impurity charges Z = 0, 1, 2, 3, and 4. In addition, we carried out the ionization energies of these QDs as a function of dot radius, and we investigated the influence of impurity on the ionization energy. We utilized the method that is a combination of quantum genetic algorithm (QGA) and Hartree-Fock Roothaan (HFR). The results are in a good agreement with literature results. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4139-4149, 2011Öğe Computation of relativistic terms in a spherical quantum dot(ELSEVIER, 2013) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanWe studied a hydrogenic impurity located at the center of a spherical quantum dot with an infinite spherical confining potential and calculated energy levels and wavefunctions using Quantum Genetic Algorithm(QGA) and Hartree-Fock Roothaan (HFR) method. In addition, we investigated the first-order relativistic terms such as the relativistic correction to the kinetic energy, Darwin and spin-orbit interaction term. These terms were calculated using the first-order perturbation theory. The electronic charge density for the Darwin term was carried out from a global operator defined by Hiller, Sucher and Feinberg. The results revealed that the relativistic corrections are important in small dot radii and they should not be neglected to improve the accuracy of calculations. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.Öğe Computation of relativistic terms in a spherical quantum dot (vol 134, pg 778, 2013)(ELSEVIER SCIENCE BV, 2013) Yakar, Yusuf; Cakir, Bekir; Ozmen, Ayhan[Abstract not Available]Öğe Computation of rotation matrices making lined-up to the local Cartesian coordinates(CHINESE CHEMICAL SOC, 2007) Yakar, Yusuf; Oezmen, Ayhan; Cakir, Bekir; Yueksel, HueseyinRotation matrices were expressed in terms of Gaunt coefficients and complex spherical harmonics. The rotation matrices were calculated using two different ways. In the first, Gaunt coefficients and normalized complex spherical harmonics were directly calculated using binomial coefficients; in the second, Gaunt coefficients and complex spherical harmonics were recursively calculated. The methods were compared with respect to accuracy and computation time (CPU) for low and very high quantum numbers.Öğe 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, UelfetThe 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.Öğe Dipole and quadrupole polarizabilities and oscillator strengths of spherical quantum dot(ELSEVIER SCIENCE BV, 2018) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, the energy eigenvalues and eigenfunctions of the ground and excited states of a spherical quantum dot are calculated by using the Quantum Genetic algorithm (QGA) and Hartree-Eock Roothaan (HFR) method. Based on the calculated energies and wave functions, the static and dynamic dipole polarizabilities, the quadrupole polarizability, dipole and quadrupole oscillator strengths of spherical quantum dot are carried out as a function of dot size and the confining potential as perturbative. The results show that dot size and confining potential have a great influence on the polarizability and oscillator strength. It is found that the polarizability increases due to the spatial confinement effect in the strong confinement region. In the weak confinement region, the polarizability increases again until it reaches the saturation value. In addition, the peak positions of the dipole and quadrupole oscillator strengths shift toward smaller dot radii with the increases of the potential well depth.Öğe Electronic structure and relativistic terms of one-electron spherical quantum dot(ELSEVIER SCIENCE BV, 2013) Ozmen, Ayhan; Cakir, Bekir; Yakar, YusufWe calculated the energy eigenvalues and eigenfunctions of the ground and excited states of a hydrogenic impurity located at the center of a spherical quantum dot using the Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (HFR) method. In addition, we carried out the relativistic effects such as the relativistic correction to the kinetic energy, spin-orbit and Darwin terms by using the perturbation method. The electronic charge density for the Darwin term is computed from the Hiller, Sucher and Feinberg formulation instead of the traditional delta function operator. The results show that impurity, dot radius and confining potential have a great influence on the relativistic effects. In addition, as the absolute value of confining potential increases, the peak values of relativistic corrections increase and move toward lower dot radii. (C) 2013 Elsevier B.V. All rights reserved.Öğe Electronic structure of two-electron quantum dot with parabolic potential(TAYLOR & FRANCIS LTD, 2015) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, we investigate the parabolic potential effects on the ground and excited energy states of two-electron quantum dot with impurity inside an infinite spherical confining potential well. The wave function and energy eigenvalues were calculated using a modified variational optimization procedure based mainly on quantum genetic algorithm and Hartree-Fock-Roothaan method. The results show that the parabolic potential and impurity charge have a strong effect on the energy states and ionization energies. It is worth pointing out that as impurity charge increases, the ionization energy rises, but the ionization dot radius decreases. On the other hand, as parabolic potential increases, the ionization energy decreases, but the ionization dot radius increases.Öğe 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, YusufIn 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.Öğe Investigation of magnetic field effects on binding energies in spherical quantum dot with finite confinement potential(ELSEVIER SCIENCE BV, 2017) Cakir, Bekir; Yakar, Yusuf; Ozmen, AyhanThe magnetic effects on the energy states and binding energies of the ground and higher excited states of the spherical quantum dot are studied theoretically for various potential depths. Also, Zeeman transition energies in the case of Delta M = 0, +/- 1 are carried out. The results show that the energy states and binding energies in small dot radii are insensitive to the increase of magnetic field. In the case of negative m, in the strong confinement region, the binding energy increases as the confinement potential decreases. In the case of positive m, the binding energy decreases with the decrease of the confinement potential. (C) 2017 Elsevier B.V. All rights reserved.Öğe Linear and nonlinear absorption coefficients of spherical quantum dot inside external magnetic field(ELSEVIER SCIENCE BV, 2017) Cakir, Bekir; Yakar, Yusuf; Ozmen, AyhanWe have calculated the wavefunctions and energy eigenvalues of spherical quantum dot with infinite potential barrier inside uniform magnetic field. In addition, we have investigated the magnetic field effect on optical transitions between Zeeman energy states. The results are expressed as a function of dot radius, incident photon energy and magnetic field strength. The results present that, in large dot radii, the external magnetic field affects strongly the optical transitions between Zeeman states. In the strong spatial confinement case, energy level is relatively insensitive to the magnetic field, and electron spatial confinement prevails over magnetic confinement. Also, while m varies from -1 to +1, the peak positions of the optical transitions shift toward higher energy (blueshift).Öğe Linear and nonlinear absorption coefficients of spherical two-electron quantum dot(ELSEVIER, 2015) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanIn this study, optical properties of two-electron quantum dot confined by an infinite spherical potential surface have been investigated. Linear, nonlinear and total absorption coefficients of S -> P, P -> D and D -> F dipole-allowed transitions between singlet-singlet and triplet-triplet states have been calculated as a function of dot radius and photon energy. The results show that the change of dot radius and incident optical intensity effects the peak positions and amplitudes of linear and nonlinear absorption coefficients. Besides, it has been found that the absorption coefficients of transitions between triplet states are stronger than those of the singlet states, and also triplet absorption transitions occur at higher energies. (C) 2014 Elsevier B.V. All rights reserved.Öğe Linear and nonlinear optical absorption coefficients of two-electron spherical quantum dot with parabolic potential(ELSEVIER SCIENCE BV, 2015) Cakir, Bekir; Yakar, Yusuf; Ozmen, AyhanLinear and nonlinear absorption coefficients of two electron spherical quantum clot (QD) with parabolic potential are investigated in this paper. Wave functions and energy eigenvalues of the 1s(2), 1s1p, 1s1d and 1s1f electronic states have been computed by using an optimization approach, which is a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock Roothaan (I-IFR) method. It is found that the strength of S -> P transition is stronger than P -> D and D -> F transitions. Also the peak positions and amplitudes of the absorption coefficients are sensitive to the electron spin. It should be noted that the peak positions and amplitudes of absorption coefficients are strongly dependent on the parabolic potential. Additionally, dot radius, impurity charge, incident optical intensity and relaxation time have a great influence on the linear and nonlinear absorption coefficients. (C) 2014 Elsevier B.V. All rights reservedÖğe Magnetic field effects on oscillator strength, dipole polarizability and refractive index changes in spherical quantum dot(ELSEVIER SCIENCE BV, 2018) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanWe have computed the ground and excited state energies and the wave functions of a spherical quantum dot with finite potential barrier in the presence of magnetic field. The oscillator strength, the static dipole polarizability and the refractive index changes are investigated as a function of dot radius and magnetic field strength. The results show that the energy state, the oscillator strength, the static dipole polarizability and the refractive index changes are strongly affected by the magnetic field strength and dot size. It is found that while the magnetic field strength increases, the static polarizability decreases strongly.Öğe Off-center hydrogenic impurity in spherical quantum dot with parabolic potential(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2013) Yakar, Yusuf; Cakir, Bekir; Ozmen, AyhanThe binding energies of 1s-, 2p-, 3d- and 4f-states of a spherical quantum dot (QD) with parabolic potential are investigated by using the perturbation method. The binding energies are calculated as a function of impurity position. The results show that the dot radius and the parabolic potential have a great effect on the binding energies and there is a linear relationship between the dot radius and impurity shift corresponding to the binding energy maximum. In addition, the binding energies show a strong dependence on the impurity position within the dot. While the binding energies for s-state have the maxima for an on-center impurity case, the binding energy maxima of the p-, d- and f-states take place at different points between the center and edge of the dot (C) 2013 Elsevier Ltd. All rights reserved.
