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Öğe The Atomic Structure of Lattice-Mismatched Si/Ge Bulk Heterostructures by Using the Density Functional Theory(E D P Sciences, 2011) Dalgic, S.; Guler, S.We present results for the atomic structure of lattice-mismatched Si/Ge bulk heterostructures by first-principles calculations based on the density functional theory. We also analyze the ground state, lattice constant, total energy, and average effective potential of Si/Ge bulk heterostructures which are modeled as monolayer and bilayer in the (001) direction investigated by using the plane wave self consistent field. Finally, an obvious difference between effective potentials of Si and Ge is observed in the result of calculations. It has been useful in the making of quantum wells of materials such as Si and Ge. Therefore, it has an important role in the invention of electronic and opto-electronic devices.Öğe The EAM based effective pair potentials for the dynamic properties of liquid Cu(Elsevier Science Sa, 2007) Dalgic, S.The effective pair potentials based on the different versions of embedded atom method (EAM) have been applied to investigate the dynamic properties of liquid copper. The presented potentials are used for the first time for this purpose. The computations were carried out using the variational hypernetted chain (VMHNC) liquid state theory in order to obtain static structure factors and pair distribution functions as a function of temperature above its melting. The dynamical properties evaluated within the framework of the mode-coupling theory, using a self-consistent scheme have been also presented. The single-particle and collective time-dependent properties of liquid copper have computed and used to calculate one of the transport coefficient, namely the self-diffusion constant D. The values for the diffusion coefficients calculated by different versions of EAM based potentials are consistent with each other. The density-dependent effective pair potentials based on EAM have been considered and determined its effects on the collective dynamic properties such as the intermediate scattering functions and the dynamic structure factors. (C) 2007 Elsevier B.V. All rights reserved.Öğe Effective pair potentials for molten Cu-Ge alloys(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Celtek, M.; Dalgic, S.The local evanescent core type electron-ion potentials (EC) constructed by Nogueira and co-workers have been applied to molten Cu-Ge alloys at different compositions of Ge. The structure properties of liquid Cu-Ge alloys, such as partial static structure factors and pair distribution functions have been calculated using the variational modified hypernetted chain (VNHNC) integral equation theory of liquids. Comparison of the structural results with experimental data confirms the ability of the universal density dependent version of the EC potential to be used in the case of liquid Cu-Ge alloys. With the change of temperature, the diffusion coefficients of the pure components and alloy obtained from the average mean-square displacement can be fitted by the Arrhenius equation. The fit yields an activation energy and pre-exponential factor. The diffusion coefficients for pure components near their melting points are in a good agreement with experimental values.Öğe Electric field and concentration effects on the binding energy of a non-hydrogenic donor impurity in a finite cylindrical quantum well wire(Natl Inst Optoelectronics, 2009) Dalgic, S.; Ozkapi, B.The effects of the electric field and concentration on the non-hydrogenic binding energy of a shallow donor impurity in a finite cylindrical quantum well wire (CQWW) of GaAs/ AlxGa1-xAs was investigated. Within the effective mass approximation, we have calculated the non-hydrogenic binding energy of donor impurity by a variational method as a function of applied electric field, the wire radius, donor impurity positions and concentration of Al. We have investigated the concentration effect of Al on the non-hydrogenic binding energy as a function of electric field, wire radius and impurity position in QWW. It is shown that the difference in donor binding energy in the hydrogenic and non-hydrogenic regimes varies with radius of QWWs and impurity position while the interplay of the electric field is the same.Öğe Electronic and structural properties of large lattice-mismatched Si/BP superlattice(Natl Inst Optoelectronics, 2011) Ozkapi, B.; Guler, S.; Dalgic, S.We present results for electronic and structural properties of large lattice mismatched Si/BP superlattice by first principle calculations based on the density functional theory. A self-consistent pseudopotential calculation has been pet-formed at Si/BP (001) strained interface. We also analyze the total energy of ground state, lattice constant and electrostatic potential line up of heterojunction between Si/BP zincblende compounds. Finally, we have investigated electronic band structure and the effect to electrostatic potential line up of structural details at interface of this system.Öğe An interface study of c-BP/c-GaN heterostructure(Natl Inst Optoelectronics, 2011) Ozkisi, H.; Kiragasi, A.; Dalgic, S.We present the modeled a superlattice for cubic-GaN on BP structure at (001) direction. The modeling procedure was achieved by using first principle calculations based on the density functional theory with Plane Wave Self Consistent Field. We also report the total energy of ground state, lattice constant, electronic band structure and potential energy line up of heterojunction between c-BP/c-GaN compounds. The effects of interface have been investigated in this system.Öğe An investigation of the local structure and dynamic properties of undercooled liquid silicon using the orbital-free ab-initio molecular dynamics method(Springer Heidelberg, 2011) Colakogullari, M.; Dalgic, S.; Gonzalez, L. E.; Gonzalez, D. J.We present results for the static and dynamic structural properties of undercooled liquid Si, at several temperatures between 1550K and 1100K, obtained through orbital-free ab-initio molecular dynamics simulations. The local bond angle distributions show a modest increase in the tetrahedral order upon decreasing the temperature. We also analyze the variation of several dynamic magnitudes and transport properties with temperature, showing a tendency to sustain shear waves for some wavevectors as undercooling is deepened. We compare our orbital-free ab-initio results with the limited experimental data available, as well as with results of other ab-initio simulations.Öğe Modelling study of liquid chalcogenide of Se20Te80 alloy depending on temperature(Natl Inst Optoelectronics, 2009) Dalgic, S.; Yavuz, S. S.; Colakogullari, M.The structural properties of the liquid chalcogenicle of Se20Te80 alloy have been calculated using Reverse Monte Carlo (RMC) modelling technique at three thermodynamic states which are at 420 degrees C, 530 degrees C and 650 degrees C. The quality of models has been improved using fitting procedure to neutron diffraction data. The atomic configurations and bond angle distributions of these systems have been calculated. The static structural functions of the liquid chalcogenide alloy belong to the resulting model where used plausible constraints have been compared with available experimental values. Finally, the obtained results correspond to related thermodynamic states show that the RMC modelling technique can be used to product three-dimensional atomic configurations.Öğe A modelling study on liquid arsenic tritelluride: reverse Monte Carlo modelling(Natl Inst Optoelectronics, 2009) Dalgic, S.; Colakogullari, M.The Reverse Monte Carlo (RMC) technique was performed to obtain a model for Arsenic Tritelluride, As2Te3, which is at liquid phase, fitting to neutron diffraction total static structure factor. The understanding of structure of this kind of materials is increasingly having importance and the atomic structures need to create a realistic model whereas the model is not unique. In order to analysis of the structure we have only investigated to describe the trend in structural terms. Thus, we have shown and have analyzed the modelling results of both the partial pair distribution functions and the partial static structure factors. Also the correctness of model was determined by what we have calculated the distribution of the number within first co-ordination shell for each pair and the bond angel distributions for each triplet. During the construction of model we have used plausible constraints which are include chemical properties such as minimum and maximum bond lengths and average coordination numbers. Finally, the modelled liquid chalcogenide structure was visualized to produce a three-dimensional atomic image. The calculated results of all these properties using RMC modelling are in good agreement with both experimental data and other theoretical calculations.Öğe Molecular structure calculations of monomeric and dimeric of rare earth chlorides(Natl Inst Optoelectronics, 2009) Dalgic, S.; Caliskan, M.In this work, the molecular geometries and vibrational frequencies of selected rare-earth trichlorides (YCl3, CeCl3, DyCl3) and their dimerics were computed using the interionic force model. In order to the determine of the model parameters, we have fitted the measurement value of the breathing mode of molecular dimerics in molecular structure calculations. It has been indicated that the ground state structures of monomeric rare-earth thrichlorides have D-3h symmetry and their dimerics have D-2h symmetry. The results for the equilibrium bond lengths, bond angles and vibrational frequencies are compared with the measured values obtained from electron diffraction and with the results of other theoretical calculations. The agreement can be considered as very reasonable.Öğe THE STRUCTURAL AND ELECTRONIC PROPERTIES OF n-POLYPYRROLE/ HOLLOW GOLD MONOLAYER HYBRID NANOSTRUCTURES BY AB-INITIO SIMULATIONS(Virtual Inst Physics, 2019) Dalgic, S. S.; Yavuz, S. S.; Dalgic, S.; Kandemirli, F.In this work, we have investigated the new generation hybrid nanostmctures combined with n-Polypyrolle monomer and hollow Au monolayer surfaces by ab-inito simulation method. Interfacial interactions between n-PPy monomer and the hollow FCC Au monolayer surfaces have obtained by density functional calculations (DFT) using the GAUSSIAN 09 program package. We have considered the one and two monomer of PPy located at inner part of hollow monolayer of gold (100) surfaces. Optimized geometry, Quantum chemical calculations of hybrid nanostmctures have obtained. The results show that the interface energy increases the number of PPy monomer increases. And depends on the position of the n-PPy deposited in the hollow Au (100) monolayer. It has found that the electron transfers from n-PPy to monolayer surface of the hybrid structure.Öğe Structure of liquid CdTe alloys using local evanescent core pseudopotential(Natl Inst Optoelectronics, 2007) Dalgic, S.; Colakogullari, M.There are presented the results of a test of transferability of the local evanescent core (LEC) pseudopotential proposed by Fiolhais et. al. to the chalcogen liquid alloys. The test is a comparison of the static structure of simple liquid metals and liquid CdTe alloys with the experimental results. The structural properties are calculated using the Variational Modified Hypernetted Chain (VMHNC) liquid state theory. It has been found that the liquid structure obtained using the LEC pseudopotential is in better agreement with the experimental data than other potentials.
