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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 Elecric field effect on the binding energy of a non-hydrogenic donor mpuirfty in a cylindrical cross-sectional quantum well wire(Wiley-V C H Verlag Gmbh, 2004) Ulas, M; Cicek, E; Dalgic, SSThe effect of an electric field on the non-hydrogenic binding energy of a shallow donor impurity in a cylindrical cross-sectional GaAs-(Ga,Al)As quantum well wire (QWW) was investigated. Within the effective mass approximation, the non-hydrogenic binding energy of the donor impurity was calculated by a variational method as a function of the wire radius, donor impurity position and applied electric field. The results show that the non-hydrogenic binding energy of the donor impurity located around the centre is larger than that of the hydrogenic binding energy. The difference in binding energy of an on-centre shallow donor impurity in the two regimes increases more rapidly with decreasing QWW radius than for other impurity positions. It has been found that the sensitivity of the donor binding energies to the applied electric field in both regimes is almost the same. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in a coaxial quantum well wire(Elsevier Science Bv, 2005) Aktas, S; Boz, FK; Dalgic, SSThe effect of both an electric and magnetic field on the hydrogenic binding energy of a shallow donor impurity in a coaxial GaAs-(Ga, Al)As quantum well wire (QWW) has been investigated as a function of the impurity position and barrier thicknesses for different values of the applied magnetic and electric field strengths. Within the effective mass approximation, the ground-state energy in the presence of a uniform magnetic field applied parallel to the wire axis has been calculated using the fourth-order Runge-Kutta method. The ground state binding energy under applied electric field has been studied with a variational approach. The two sharp increase in the binding energy have observed for the donor impurity located at outside of the center under the critical electric and magnetic field values. However, for the electric field off the binding energy monotonously decrease with increasing magnetic field strength up to a critical magnetic field and then a sharp decrease is seen before reaching a constant value. For the impurity located at the center, the abrupt deviations of the binding energy strongly depend not only on the electronic confinement, but also on the electric and magnetic field strength. We expect that these results will be useful in technological applications. (c) 2005 Elsevier B.V. All rights reserved.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 Ion-electron pseudopotentials for liquid alloys with small charge-transfer effects(Elsevier Science Bv, 1996) Gonzalez, LE; Dalgic, SS; Gonzalez, DJ; Silbert, MA formalism for computing pseudopotentials for alloys is presented which introduces small charge-transfer effects, so that metallic bonding is still dominant. In this work, the pseudopotentials are calculated by taking into account, through averages, the presence of the two types of ions using the neutral pseudoatom method and by allowing for small chemical effects through charge transfer from the conduction band to one of the components of the alloy. Two possible models for the charge transfer are discussed. Results are presented for a liquid Li-Ba alloy as a test case.Öğe The liquid structure of CdTe alloy using the ameam potentials(Natl Inst Optoelectronics, 2005) Dalgic, SS; Sengul, S; Kalayci, SThe structure of molten cadmium telluride have been calculated using the integral equation theories with the effective pair potentials based on the analytic modified embedded atom method (AMEAM). The pair interactions are described with the semi-empirical potential functions recently proposed Hu and co-workers. All the potential parameters for pure components are determined by fitting both liquid and solid state properties. The structural properties of liquid Cd-Te equiatomic alloy have been obtained using the Variational Modified Hypernetted Chain liquid state theory. The results of partial pair distribution functions are compared with the neutron diffraction data and those obtained by Stillinger-Weber semi-empirical potential.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 On the static dielectric function of liquid metals(Springer, 1997) Gonzalez, LE; Silbert, M; Gonzalez, DJ; Dalgic, SSA formalism is presented for the calculation of the dynamic dielectric function, epsilon(k,w), of simple liquid metals. This is based on the assumptions that the liquid metal may be regarded as an isotropic and homogeneous binary mixture of classical rigid ions and conduction electrons which interact weakly with one another. The formalism is applied to study the static dielectric function, epsilon(k,0), of the liquid alkali and alkaline-earth metals near their melting points. Specifically, the calculations make use of the Neutral Pseudo Atom pseudopotential, the Local Density Approximation dielectric function and the Variational Modified Hypernetted Chain theory of liquids. The whole theory is free of adjustable parameters and uses as input data the thermodynamic state of the system (ionic number density and temperature), the valence, and the atomic number. The obtained results show that the behaviour of the dielectric function of the simple liquid metals, near their melting points, is dominated by the ionic contributions.Öğe Self polarization in GaAs-(Ga, Al)As quantum well wires: electric field and geometrical effects(Elsevier Science Bv, 2005) Ulas, M; Erdogan, I; Cicek, E; Dalgic, SSThe response of an electron to an external electric field in different shapes of infinite quantum well wires has been investigated. The self-polarization effect which can be defined as the influence of the barrier potential on the impurity electron is studied for the quantum well wire of square, rectangular and cylindrical cross-sections. An external electric field vanishes due to the self-polarization effect has been calculated. It is shown that the self-polarization effect outside of the center depends on both the geometrical form of the wire and the impurity position in the same structure. (C) 2004 Elsevier B.V. All rights reserved.Öğe Semi-empirical potentials for CuI(Natl Inst Optoelectronics, 2005) Dalgic, SS; Gurbuz, H; Caliskan, M; Ozgec, OWe have investigated the prospects for developing semi-empirical model potentials for use in the studies of structural properties of CuI with integral equation theories. The point of view adopted requires that only short range two atom and three atom interactions appear. A three-body potential of Tersoff has been tasted with the hypernetted chain integral equation by calculating the pair correlation function for CuI at 710 K. The two-body and three-body Kohen-Tully-Stillinger empirical interatomic potential has been applied. The structural results of liquid CuI have been compared with experiment and those obtained by rigid ion potentials.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 Structural properties of liquid K-Te alloys(Natl Inst Optoelectronics, 2005) Tezgor, G; Dalgic, SS; Domekeli, UThe structure of K-Te liquid alloys at two different stoichiometric compositions was determined using the effective pair potentials based on the modified analytic embedded atom method (MAEAM) with the Variational Modified Hypernetted Chain (VMHNC) liquid state theory. The MAEAM potential functions are fitted to both solid and liquid state properties for only pure liquid metals. A new effective pair potential form based on the MAEAM has been proposed for the best possible structural properties of these alloys, The partial pair correlation functions for the K0.12Te0.88 at T = 723 K and equiatomic KTe at 770 K have been obtained. The results are in reasonably good agreement with experiments and MD results.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.
