Ayhan Özmen

Linear and Nonlinear Optical Properties in Spherical Quantum Dots

We calculate the energy eigenvalues and the sate functions of one-electron Quantum Dot (QD) by using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method. The linear and the third-order nonlinear optical absorption coefficients for the 1s-1p, 1p-1d, and 1d-1f transitions are examined as a function of the incident photon energy for three different values of the stoichiometric ratio. The results show that the stoichiometric ratio, impurity, relaxation time, and dot size have great influence on the optical absorption coefficients of QDs.

CALCULATION OF ELECTRONIC STRUCTURE OF A SPHERICAL QUANTUM DOT USING A COMBINATION OF QUANTUM GENETIC ALGORITHM AND HARTREE–FOCK–ROOTHAAN METHOD

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 wavefunctions 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.

Investigation Of Electronic Structure Of A Quantum Dot Using Slater-Type Orbitals And Quantum Genetic Algorithm

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-Fock-Roothaan (HFR) method. The orbital exponent ζis and the expansion coefficient cis 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.

Electronic structure of two-electron quantum dot with parabolic potential

In 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.

Linear and nonlinear absorption coefficients of spherical two-electron quantum dot

Abstract In 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.

ESR study of γ-Irradiated N α -Acetyl-L histidine monohydrate

The electron spin resonance of γ-irradiated single crystals of N α -Acetyl-L Histidine Monohydrate, C 8 H 11 N 3 O 3 .H 2 O has been observed and analysed for different orientations of the crystal in the magnetic field. The crystals have been investigated between 100 and 400 K. The spectra were found to be temperature independent and the radiation damage centres are attributed to R 1 -NH (σ radical), R 2 -NCH (π radical) and C 2 H 2 CH 2 . The g and hyperfine coupling constants were found to be almost isotropic with an average g = 2.0045, a N =10 G, a H = 130 G for R-N H and g = 2.0042, a H = 90 G, a N = 10 G for R 2 -NC H and g = 2.0047, a H = 30 G, a Hβ = 10 G for C 2 H 2 CH 2 .

Molecular structure and vibrational spectra of alpha-benzoinoxime by density functional method

In the present study, an exhaustive conformational search of the Alpha-benzoinoxime has been performed. The FT-IR spectrum of this compound was recorded in the region 4000–400 cm−1. The FT-Raman spectrum was also recorded in the region 3500–50 cm−1. Vibrational frequences of the title compound were calculated by B3LYP method using 6–311++G(d, p) basis set. The calculated vibrational frequences were analysed and compared with experimental results.

Experimental and theoretical research on γ-irradiated 7-methoxy-4-methylcoumarin powder through EPR and DFT methods

ABSTRACT In this paper, the effects of gamma irradiation on 7-Methoxy-4-methylcoumarin (7M4MC) molecule, an essential coumarin derivative, which has an inherent variety of biological activities, therapeutic properties and industrial usage were examined. For this purpose, the sample was irradiated with 60Co-gamma ray source for about 100 kGy total doses. Theoretical calculations were performed using GAUSSIAN03 program for the possible radicals that were modeled from two stable conformations with lowest energies. In order to get well-resolved spectra and to determine the radical identity experimentally, EPR spectra of the irradiated 7M4MC sample were recorded at several spectrometer conditions. By considering the molecular structure and EPR spectra, alkyl-type radical was assumed to be formed by gamma irradiation. To support the estimations, simulations were done using theoretical EPR parameters as an initial value. The experimental spectra were well matched with the sum of simulated spectra obtained from two same type modeled radicals of two different conformations. As a result of experimental estimations and theoretical calculations, radiation-induced radicals were identified as two neutral alkyl radicals, , originated from two stable conformations.

Investigation of Radiation Effects on Coffee Beans Using ESR Technique

Bu calismada kahve cekirdegi uzerine radyasyonun etkisi Elektron Spin Rezonans (ESR) teknigiyle incelenmistir. Dogal ve 60 Co gama kaynagi ile 0.5 Gy ile 11 kGy doz araliginda farkli dozlarda isinlanmis orneklerin spektrumlari X-band ESR spektrometresiyle kaydedilmis ve olusan paramanyetik merkezlerin radyasyona, ESR mikrodalga gucune ve kavite sicakligina bagli degisimleri arastirilmistir. Doz-cevap ve kinetik calismalar sonucunda kahve cekirdegindeki paramanyetik merkezin radyasyona duyarli ve kararli oldugu belirlenmis, incelenen doz araliginda dozimetrik amacli ve isinlanmis gida dedeksiyonu icin kullanilabilirligi gosterilmistir.

EPR study of gamma-irradiated 2-Bromo-4′-methoxyacetophenone single crystals

ABSTRACT The gamma-irradiated single crystals of 2-Bromo-4′-methoxyaceto-phenone (2B4MA) were investigated using electron paramagnetic resonance (EPR) technique. Density-functional theory calculations were employed to investigate and identify the radicals that have been assumed to be formed upon irradiation of 2B4MA single crystals. The EPR spectra of 2B4MA were recorded at different orientations in the magnetic field at room temperature. Taking into account the chemical structure and experimental spectra of irradiated single crystal of 2B4MA, it was assumed that at least two different radicals were produced in the sample. Following this assumption, six possible radicals were modeled and EPR parameters were calculated by using the DFT, B3LYP/6-311+G(d), for the modeled radicals individually. The calculated hyperfine coupling constants and g-tensors were used as initial values for simulation studies. The three crystallographic axes on the simulated spectra were well matched with experimental spectra for the two modeled radicals. Thus, we identified the R1 type radical and R4 type radical as paramagnetic species produced in gamma-irradiated 2B4MA.