Yazar "Dalgic, S" seçeneğine göre listele
Listeleniyor 1 - 10 / 10
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Calculations of atomic dynamics in simple liquid metals(Natl Inst Optoelectronics, 2005) Dalgic, S; Colakogullari, M; Dalgic, SSWe present several dynamical properties of liquid Li, Rb, and Cs near their melting points. They have been evaluated within the framework of the mode-coupling theory, using a self-consistent scheme that uses as input data only the static structure functions and the interatomic pair potantials of the simple liquid metals. In this work we have used the interatomic pair potential which is derived from second order perturbation theory with Fiolhais electron-ion pseudopotential. We carried out theoretical results to compute single-particle and collective time-dependent properties of liquid metals, and thereby to calculate their self diffusion constants. We have discussed our results in comparison with both experiment and molecular dynamics simulation.Öğe Electric field effect on the binding energy of a non-hydrogenic donor impurity in a square quantum well wire(Natl Inst Optoelectronics, 2005) Dalgic, S; Ulas, M; Ozkapi, BWe have used a variational technique to calculate the effect of an electric field on the non-hydrogenic binding energy of a donor impurity in a square GaAs/Ga1-x AlxAs quantum well wire (QWW). The non-hydrogenic binding energy of the donor impurity was calculated by the variational method as a function of applied electric field, the wire radius and donor impurity position. The results show that the non-hydrogenic binding energy of donar impurity located around the centre is larger than that of the hydrogenic binding energy. In this work, the variational method employed is capable of giving all the correct trends for impurity binding energies as a function of applied electric field, impurity position and screening effect.Öğe Interatomic pair potentials and liquid structure of some HCP rare-earth metals(Natl Inst Optoelectronics, 2003) Dalgic, SS; Dalgic, S; Celtek, M; Sengul, SEffective pair potentials for some HCP liquid rare-carth metals near their melting points have been derived from the second order perturbation theory with the Heine-Abarenkov pseudopotential and the transferable electron-ion potential of Fiolhais and coworkers which was originally developed for the solid state. We have also constructed the Wills-Harrison (WH) model potentials. The s electron contribution to the effective potential has been taken into account with these potentials using different screening functions. in this work, recently proposed Karmakar-Joarder form of modified WH potentials has been applied to some HCP liquid metals, as Tb, Dy, Ho, Er and Lu in order to obtain the d state and f state contributions. The Singh form of WH potentials has also been calculated for comparison with those obtained by others. The liquid structure has been computed with both random phase approximation and the variational modified hypernetted chain (VMHNC) integral equation theory. It has been shown that the VMHNC results of static structure factors and pair distribution functions are in good agreement with the experimental data.Öğe Liquid structure of some rare-earth metals using an analytic pair potential(Natl Inst Optoelectronics, 2001) Dalgic, SS; Dalgic, S; Sengul, S; Celtek, M; Tezgor, GThe analytical Pettifor-Ward (PW) pair potential with the Ashcroft empty core model for the pseudopotential is employed to obtain structural properties of some liquid rare-earth metals. The liquid structure is calculated using the variational modified hypernetted chain (VMHNC) approximation. Recently proposed the modified Harrison model potential (MH) of Karmakar and Joarder has been calculated using the PW pair potentials for s electron contribution for comparison. A good agreement with the experimental data for structural properties has been found. However, VMHNC calculations using MH potential fail to yield reasonable results if one used Karmakar's data set.Öğe Modelling the structure factors and pair distribution functions of amorphous germanium, silicon and carbon(Elsevier Science Bv, 2002) Dalgic, S; Gonzalez, LE; Baer, S; Silbert, MWe present the results of calculations of the static structure factor S(k) and the pair distribution function g(r) of the tetrahedral amorphous semiconductors germanium, silicon and carbon using the structural diffusion model (SDM). The results obtained with the SDM for S(k) and g(r) are of comparable quality with those obtained by the unconstrained Reverse Monte Carlo simulations and existing ab initio molecular dynamics simulations for these systems. We have found that g(r) exhibits a small peak, or shoulder, a weak remnant of the prominent third neighbour peak present in the crystalline phase of these systems. This feature has been experimentally found to be present in recently reported high energy X-ray experiments of amorphous silicon (Phys. Rev. B 60 (1999) 13520), as well as in the previous X-ray diffraction of as-evaporated amorphous germanium (Phys. Rev. B 50 (1994) 539). (C) 2002 Elsevier Science B.V. All rights reserved.Öğe The single step inverse calculations of the effective pair potentials for liquid lithium(Natl Inst Optoelectronics, 2004) Dalgic, S; Dalgic, SSIt is presented the revised effective pair potentials for liquid lithium extracted from experimental structure data using the inverse method, which is based on the variational modified hypernetted-chain(VMHNC) integral equation theory of liquids. The reliability of the revised potential is supported by a comparison the neutral pseudoatom potential at several thermodynamic states. Although the single-step VMHNC inversion yields acceptable results for the characteristic features of the density dependence of the revised potentials for liquid lithium, the difference in the medium behaviour of the Li potential is a cause of concern. This discrepancy and the limitations of the approximate theories in the inverse calculations have been discussed with the possible improvements.Öğe Structure of less simple liquid alloys(Natl Inst Optoelectronics, 2005) Kes, H; Dalgic, SS; Dalgic, SThe transferability of the local evanescent core (EC) pseudopotential to less-simple liquid binary alloys is assessed. The structural properties of liquid Ag-In alloys at different compositions are calculated using the Variational Modified Hypernetted Chain (VMHNC) integral equation theory of liquids with the effective pair potentials derived from the evanescent core electron-ion potential constructed by Nogueira, Fiolhais and Perdew for the solid state. Comparison with the results those obtained by other different forms of the model pseudopotentials and experimental data confirms the ability of the universal density dependent version of the EC potential to be used in the case of liquid less-simple metals and metal alloys.Öğe Structure of liquid alikaline earth metals and metal alloys using a new transferable local pseudopotential(Natl Inst Optoelectronics, 2003) Kes, H; Dalgic, SS; Dalgic, S; Tezgor, GIn this work, we have obtained the structural properties of liquid Ca, Sr and Ba near their melting points using the thermodynamically self consistent liquid state theory, the variational modified hypernetted chain (VMHNC) approximation with the effective pair potentials which are derived from the second order perturbation theory using the recently proposed transferable electron-ion potential of Fiolhais and co-workers. One has been noted that this potential is non realistic for the alkaline earths (Ca, Sr, Ba) because of the strongly nonlocal character. In this work, it has been shown that the computed structure factors and pair distribution functions near their melting points are in good agreement with experimental data. It has been also applied to the liquid alloys to predict the pair interactions and the partial structure factors by taking Li-Ba. as a model alloy, The structural properties of Li-Ba alloys are presented for different concentrations by comparing with experimental data.Öğe Structure properties of liquid FCC transition metals using the embedded atom method potential(Natl Inst Optoelectronics, 2003) Dalgic, SS; Dalgic, S; Domekeli, UThe liquid structure calculations for fcc transition metals using the variational modified hypernetted chain liquid state theory with a new embedded atom method (EAM) model have been presented. In this model, an analytic construction of a many - body potential inspired from the Mishin et. al. [Phys. Rev. B 63, 224106, 2001] potential functions is presented. The new model has been applied to calculate the structural properties of fcc transition metals for Cu, Ag, Au and Ni near their melting points. The computed static structure factors and pair distribution function are in good agreement with the experimental data.Öğe Transferable pair potentials for liquid iron, cobalt and nickel(Taylor & Francis Ltd, 2002) Dalgic, SS; Dalgic, S; Tezgor, GEffective inter-ionic pair potentials for liquid iron, cobalt and nickel are derived from second order pseudopotential perturbation theory with the transferable electron-ion potential of Fiolhais and co-workers which was originally developed for the solid state. The liquid structure is obtained by the thermodynamically self consistent liquid state theory, the variational modified hypernetted chain (VMHNC) approximation. It has been found that the calculated structural properties at the investigated thermodynamic states just above the melting point agree well with experiment. In this work we have determined the parameters of liquids Fe, Co and Ni for the universal choice of the evanescent core pseudopotentials of Fiolhais'. We have shown that this pseudopotential is transferable to the liquid state if used this parameterisation.
