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Öğe Atomic transport properties in barium oxide using a Tersoff potential(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Ozgec, O.We present a theoretical study of transport properties in barium oxide, by a three body potential of Tersoff. The structural properties are also predicted by Variational Hypernetted Chain (VMHNC) liquid state theory. The dynamic and atomic transport properties of BaO have been studied with the viscoelastic model approximation to compute both single-particle and collective time-dependent properties. The mean-square displacement, the velocity autocorrelation function and the intermediate scattering functions have calculated and then used to compute the diffusion constant at different temperatures. There are no experimental values of the diffusion coefficients for BaO, but the values calculated our results by several independent routes are mutually consistent. For comparison, the calculations are also performed using the rigid ion model potentials.Öğe Computational Modeling of the Liquid Structure of Grossular Ca3Al2Si3O12 Glass-Ceramics(Polish Acad Sciences Inst Physics, 2016) Dalgic, S. Senturk; Guder, V.In this work, we present an atomistic model to simulate the structural and some thermodynamic properties of biomaterials as a test case of grossular glass-ceramics. The potential model used in our simulations included short range Born-Mayer type forces and long-range Coulomb interactions. We modelled the atomistic structure of grossular using the different structural optimization methods in conjunction with molecular dynamics simulations. The calculated values of the lattice constant, bulk modulus, elastic constants and cohesive energy are in reasonable agreement with experimental measurements and previous data. The melting point of grossular produced from a volume of the heating process is in a good agreement with literature. Comparison of the predictions of partial pair distribution functions and available experimental data shows that this model has simulated the liquid structure of grossular reasonably well.Öğe Effective interatomic pair potentials for liquid silver-tin alloys(Amer Inst Physics, 2007) Dalgic, S. Senturk; Kes, H.The transferability of the local evanescent core (EC) pseudopotential to liquid AgSn binary alloys have been tested. The effective interatomic pair potentials derived from the evanescent core electron-ion potential which was constructed by Nogueira and co-workers have been calculated using the second order perturbation theory. The structural properties of liquid Ag-Sn alloys at different compositions of tin have obtained using the Variational Modified Hypernetted Chain (VMHNC) integral equation theory of liquids. The results for the partial structure factors and total structure factors near their melting have been compared with experimental data. The computed structural characteristics exhibit the correct trends with experiment. It has been shown the ability of the universal density dependent version of the EC potential to be used in the case of liquid Ag-Sn simple metals and metal alloys. The charge transferred between atoms have also been investigated.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 Equilibrium structure of CuO and CuS using the interionic force model(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Canan, C.; Caliskan, M.The molecular structure of monomeric CuO and CuS has been determined by recent quantum chemical calculations and electron diffraction experiments. In the present work, the molecular dynamics of the interionic force model has been applied to obtain the equilibrium structure of these molecules. The equilibrium bond lengths and bond angles obtained have compared with the experimental data and reported values. It has been noted that the theoretical methods applied so far are mostly based on density functional theory and the reported results were much away from the experimental values. The results obtained in this work, are the overall agreement with experimental values. The partial pair distribution functions have been calculated with the HNC approximation using the interatomic pair potentials determined by the presented model.Öğe Equilibrium structure of germanium selenide GenSem clusters(Natl Inst Optoelectronics, 2010) Dalgic, S. Senturk; Caliskan, M.; Canan, C.A refined model for the interionic interactions in GenSem clusters by an analysis of data on their molecular structures has been studied. The adopted potential energy function is based on the interionic force model proposed by Akdeniz and Tosi. The microscopic model used for GenSem clusters incorporates the Born Model of cohesion and shell model for vibrational motions, bond length and crystal defects. Busing overlap repulsive energy form have been used with electron shell deformability described through the effective valences, the electric and overlap polarizabilities of the ions. The equilibrium molecular structures have also been predicted by the molecular dynamics calculations based on proposed model. It has been shown that the calculated bond lengths and bond angles are in good agreement with experimental data and those obtained by chemical structure calculations. In addition, the liquid structure of GeSe is obtained by Variational Hypernetted Chain (VMHNC) approximation and molecular dynamics (MD) simulation using the effective potential derived from the interionic force model within the polarizable ion potential.Öğe Equilibrium structure of germanium sulfur GenSm clusters(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Caliskan, M.We determine a refined model for the interionic interactions in GenSm clusters by an analysis of data on their molecular structures. The adopted potential energy function is based on the interionic force model proposed by Akdeniz and Tosi. The microscopic model used for GenSm clusters incorporates the Born Model of cohesion and shell model for vibrational motions, bond length and crystal defects. Electron shell deformability is described through the effective valences, the electric and overlap polarizabilities of the sulfurs. The two different overlap repulsive energy form have been tested. The equilibrium molecular structure has also been predicted with molecular dynamics simulation. It has been shown that the calculated bond lengths and bond angles are in good agreement with experimental data and those obtained by chemical structure calculations. In addition, the liquid structure of GeS2 is obtained by Variational Hypernetted Chain (VMHNC) approximation using the effective potential derived from the interionic force model within the polarizable ion potential.Öğe Glass forming ability and crystallization of CuTi intermetallic alloy by molecular dynamics simulation(Natl Inst Optoelectronics, 2011) Dalgic, S. Senturk; Celtek, M.In this work, we have used molecular dynamics (MD) to obtain an atomistic description of the melting, glass formation and crystallization process in CuTi alloy. We present the tight-binding (TB) many body potentials for the CuTi system which were constructed so as to reproduce a number of properties of the B11 CuTi compound (tetragonal structure). It has been shown that these potentials ensure the stability of the CuTi crystal structure against alternate structures and closely reproduce the melting temperature of CuTi. We have also considered several cooling rates to investigate its effect on the glass transition and crystallization temperatures. The pair distribution functions (PDF), Wendt Abraham (WA) parameters and the changes of volume were calculated to determine glass transition temperature and crystal formation of CuTi alloy.Öğe Liquid-to-glass transition in bulk glass-forming Cu55-xZr45Agx alloys using molecular dynamic simulations(E D P Sciences, 2011) Dalgic, S. Senturk; Celtek, M.We report results from molecular dynamics (MD) studies concerning the microscopic structure of the ternary, bulk metallic glass-forming Cu55-xZr45Agx (x=0,10,20) alloys using tight-binding potentials. Understanding of the nature of Glass Forming Ability (GFA) of studied alloys, GFA parameters, glass transition temperature (T-g), melting temperature (T-m), reduced glass transition temperature (T-g/T-m), the supercooled liquid region and other parameters were simulated and compared with experiments. The computed pair distribution functions reproduce well experimental x-ray data of Inoue and co-workers. Structure analysis of the Cu-Zr-Ag alloy based on MD simulation will be also presented.Öğe Molecular dynamics simulation studies on melting of Sn nanowires(Natl Inst Optoelectronics, 2011) Dalgic, S. Senturk; Domekeli, U.The melting process of Sn nanowires has been simulated by using molecular dynamics with the modified analytic embedded atom method (MAEAM) interatomic potentials. The wires studied here are chosen approximately cylindrical in cross-section. The periodic boundary conditions has been applied along their length; the atoms were arranged initially in a crystal structure of beta-Sn block which belongs to tetragonal group with the [0 0 1] direction parallel to the long axis of the wire. The size effects of the nanowires on the melting temperatures have been investigated. In order to characterize melting transition, we have interested in some structural, energetic and dynamical quantities of Sn nanowires. We find that for the nanoscale regime, the melting temperatures of Sn nanowires are much lower than that of the bulk. It has been resulted that melting point of Sn nanowires shifts to higher temperatures when the diameter of nanowires increased. There is in a good agreement between the results obtained from MD simulations and other theoretical and experimental data. When a nanowire is heated up above the melting temperature, the neck of the nanowire begins to arise and the diameter of neck decreases rapidly with the equilibrated running time. Finally, the breaking of nanowire arises, which leads to the formation of the spherical nanoparticles.Öğe Molecular dynamics simulations of liquid GeSe alloy: the first application of modified analytic embedded atom method (MAEAM)(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Sengul, S.We present the results of molecular dynamics (MD) simulations of liquid GeSe alloy near melting point using an effective pair potential based on modified analytic embedded atom method (MAEAM). The potential functions of MAEAM are parameterized by fitting to both solid and liquid state properties of pure Ge and Se. MD simulations have been performed to investigate the structure and the dynamical properties of liquid GeSe alloy. We have compared the total structure factor and pair correlation function, obtained in the MD simulations to the results of self consistent integral equation theory of Variational Modified Hypernetted Chain (VMHNC), experiment and other MD results. To describe the atomic dynamics in I-GeSe, we calculate the diffusion coefficient D which is directly related to the mean square atomic displacement. Viscosity of the liquid alloy is estimated by Stokes-Einstein formula. On the other hand, the MD results of dynamics in I-GeSe are compared with those obtained by the viscoelastic theory of fluids. The collective dynamic properties such as the intermediate scattering function and the dynamic structure factor have determined. We have analyzed the behaviour of self dynamic-structure factor computed in the frame of the viscoelastic model.Öğe Molecular dynamics study of the ternary Cu50Ti25Zr25 bulk glass forming alloy(E D P Sciences, 2011) Dalgic, S. Senturk; Celtek, M.The structure and thermodynamic properties of a ternary Cu50Ti25Zr25 metallic glass forming alloy in solid-liquid to glass phases were studied using molecular dynamics (MD) method based on tight-binding (TB) potentials. An atomic description of the melting, glass formation and crystallization process has been analyzed using different heating and cooling rates. The computed Glass Forming Ability (GFA) parameters are in good agreement with experimental data. The structure analysis of the Cu50Ti25Zr25 based on molecular dynamics simulation will be also presented and compared with available MD results. We have also discussed the crystallization transition with two different interatomic potentials used in this work.Öğe Size dependence of melting process of ZnSe nanowires: molecular dynamics simulations(Natl Inst Optoelectronics, 2011) Sengul, S.; Dalgic, S. SenturkIt is known that the stable crystal structure of ZnSe nanowires depends on the nanowire diameter. For this reason, we have focused on the impact of size of ZnSe nanowires on their structural properties. The molecular dynamics (MD) simulations have performed to especially discuss consequences for size effect on melting process for ZnSe nanostructures with cylindrical shape. The interactions between the atoms in system have defined by an empirical model potential developed for semiconductor metal-chalcogenides. The nanowires studied in this work have a different number of diameters and have generated by assembling the zincblende unit cell. Periodic boundary conditions have applied only along c-axis. The size effect on melting of nanowires has investigated. Some structural and dynamic properties such as distribution functions, mean square displacements and diffusion coefficients have also calculated to get detailed information about the nature of melting process of ZnSe nanowires. Calculations show that melting temperatures of ZnSe nanowires are lower than that of bulk and highly related with the size of the nanowires.Öğe Size Dependent Properties of Hollow Gold Nanoparticles: A Theoretical Investigation(Polish Acad Sciences Inst Physics, 2016) Dalgic, S. SenturkA new kind of nanostructures with the negative curvature defined as the hollow ones have recently used in biomedical applications. In this work, an analytic model was developed to compute the size-dependent properties of spherical hollow gold nanoparticles in shell-core-shell configuration. This model has established to calculate the cohesive energies based on the surface energy consideration depending on sizes of inner and outer surfaces of hollow nanoparticles. The size and geometry of the model particles have been obtained by using the stability diagram and the collapsing mechanism was studied by molecular dynamics simulations. The model has been also applied to the hollow particles within unstable and half stable geometry. The predicted results have been compared with each other and those obtained by solid ones. The theoretically predicted size dependent properties are consistent with experimental observations and the hollow quantum dot calculations. Thus, an atomistic insight into the size effect on the cohesive energies of hollow nanoparticles has been presented.Öğe Static and dynamic structure of liquid GaSb using the modified embedded atom method (MAEAM) potentials(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Domekeli, U.Using the effective potentials derived from the modified analytic Embedded Atom Method (MAEAM) in conjunction with the Variational Hypenetted Chain (VMHNC) liquid state theory, we have investigated the structure and atomic dynamics of liquid GaSb alloy near and above the melting point. The effective pair potentials have constructed from the MAEAM potential functions which are parameterized by fitting to both solid and liquid state properties of pure metals. The calculated partial pair correlation functions and static structure factors of liquid GaSb alloy near its melting have compared with experiment and the results of MD studies. The total structure factors of molten GaSb have computed at three different temperatures. The overall agreement has been found in reported works. The dynamical properties evaluated within the framework of the mode-coupling theory, using a self-consistent scheme have been also presented. The single-particle dynamics of the system has been analyzed by computing the mean square displacement (MSD) and velocity autocorrelation function (VACF). Temperature dependence of self diffusion coefficient and shear viscosity have also been shown. The collectiveÖğe Static structure of liquid K-Sb alloys using the MAEAM potentials(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Domekeli, U.The structure of K-Sb liquid alloys at different compositions of Sb have been obtained using the modified analytic EAM (MAEAM) based effective pair potentials in conjunction with the Variational Hypernetted Chain (VMHNC) liquid state theory. The effective pair potentials are constructed from the MAEAM potential functions which are parameterized with fitting to both solid and liquid state properties of pure metals. The partial pair correlation functions and total static structure factor in liquid KSb alloys are computed and than compared with experiments and the results of MD studies. The overall agreement has been found in reported works.Öğe Structural and atomic transport properties of molten zinc oxide(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Ozgec, O.We present a theoretical study of the static structure and atomic transport properties of molten Zinc Oxide using different effective pair potentials. Semi-empirical potentials such as a three body potential of Tersoff and Kohen-Tully-Stillinger have been applied. The pair correlation functions for ZnO above melting point has predicted by Variational Hypernetted Chain Liquid State theory (VMHNC). The dynamics and atomic transport properties of ZnO have been studied with the viscoelastic model approximation by computing both single-particle and collective time-dependent properties. The mean -square displacement, the velocity autocorrelation function and the intermediate scattering function have obtained inorder to compute the self diffusion coefficients at different temperatures. For comparison, the calculations are also performed using the rigid ion model potentials. It is shown that the calculated liquid structural properties predicted by Tersoff potential are in good agreement with the latest theoretical results.Öğe Structure and atomic transport properties in liquid AsTe alloys using AMEAM based potentials(Natl Inst Optoelectronics, 2007) Dalgic, S. Senturk; Sengul, S.The static, dynamic structure and atomic transport properties of liquid AsTe alloys have been calculated using the integral equation theory with the effective pair potentials based on the analytic modified embedded atom method (AMEAM). The effective pair interactions are described with the potential functions recently proposed Hu and co-workers which are parametrized by fitting the cohesive energy, vacancy formation energy and equilibrium conditions of solid and liquid state properties of pure metals. In the structural calculations for liquid AsTe alloys, the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquids has been carried out to compute the partial static structure factors. The calculated single particle and collective dynamic properties have used to obtain the atomic transport properties, such as diffusion coefficients. The results have compared with available experimental data.Öğe THERMAL BEHAVIOUR OF CdSe HOLLOW QDs STUDIED BY MOLECULAR DYNAMICS SIMULATIONS(Natl Inst R&D Materials Physics, 2017) Dalgic, S. SenturkThermally behavior of the different sizes of CdSe hollow quantum dots (HQDs) sub<10nm was first investigated by molecular dynamics (MD) simulations. The seven samples of the CdSe-HQDs within the thin wall thickness have constructed from the solid QDs with zincblende (ZB) structure at the diameter of 4-8m sizes. The size and temperature dependent cohesive energies, self-diffusion kinetics and the transformations in their morphology, thus their melting points have presented by describing the two- stage melting of HQDs. Although, the thermodynamic stability of the simulated HQDs is related to the hollow interior they contain, it is actually more concerned with their wall thickness. A two-step melting behavior is not observed for the HQDs with the diameter smaller than 5nm. However, it is identified clearly for 6nm size HQDs with two different melting modes by analyzing the self-diffusion behavior of atoms. Thus, these results can be suitable for the construction of chalcogenide HQDs with ZB structureÖğe Thermodynamic Properties of Potassium Oxide (K2O) Nanoparticles by Molecular Dynamics Simulations(Polish Acad Sciences Inst Physics, 2017) Guder, V.; Dalgic, S. SenturkPotassium oxide (K2O) is a reagent for testing the presence of other compounds in chemical reactions. It is also used in compounding cement and in glass making. However properties of K2O in nanoscale are still unclear. In this work, thermodynamic properties of spherical K2O nanoparticles have been investigated. Size dependent cohesive energy, melting point and glass transition temperature have been computed for different sizes of K2O nanoparticles by molecular dynamics simulations. Thermal expansion coefficients of nanoparticles at zero pressure and various temperatures have been also calculated. Melting point depression for K2O nanoparticles was determined. The significant change in cohesive energy was obtained for particles smaller than 5.4 nm. The presented model is successful in understanding the size-dependent thermodynamics of spherical K2O nanoparticles. Theoretical investigations of the thermal properties of K2O nanoparticles have not been presented previously.
