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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 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.