Dynamics of Liquid Na_0.5K_0.5Alloy

Abstract

An effort is made to study the motion of effective atoms in liquid Na,.,K,,, alloy in terms of velocity autocorrelation function, power spectrum, and mean square displacement analogous to the single particle motion in liquid metals employing the model developed by Glass and Rice in quasi crystalline approximation. The motions of effective atoms are also studied through the collective excitations by computing the longitudinal and transverse phonon frequencies. The results of collective excitations are in good agreement with the molecular dynamics (MD) results. Besides, results of thermodynamical properties such as isothermal bulk modulus and Debye temperature are also presented. The computed values are in good agreement with the results obtained by other theoretical calculations.Es werden Anstrengungen unternommen, um die Bewegung von effektiven Atomen in flussigen Na,,,K,,,-Legierungen mittels Geschwindigkeits-Autokorrelationsfunktion, Leistungsspektrum und mittleren Verschiebungen in Analogie zur Einpartikelbewegung in flussigen Metallen zu untersuchen, wobei das Model1 von Glass und Rice in Quasikristallnaherung benutzt wird. Die Bewegungen der effektiven Atome werden auch mit kollektiven Anregungen durch Berechnung der longitudinalen und transversalen Phononfrequenzen untersucht. Die Ergebnisse der kollektiven Anregungen sind in guter Ubereinstimmung mit Ergebnissen der Molekulardynamik (MD). Dariiberhinaus werden die thermodynamischen Eigenschaften, wie isothermer Elastizitatsmodul und Debye-Temperatur, ebenfalls angegeben. Die berechneten Werte sind in guter Ubereinstimmung mit den Ergebnissen, die durch andere theoretische Berechnungen erhalten werden. IntroductionDuring the past two decades the field of liquid state physics has seen remarkable advances both in experimental procedures and in theoretical understanding. The analysis of these liquids is complicated by the presence of many-body forces acting between the atoms and ions. Fortunately, it is possible to construct a theoretical framework that defines effective two-body potentials that are in good agreement with experimental data for the liquid state. Much of the experimental data used to investigate properties of the liquids come from X-ray and neutron scattering studies.In recent years there has been a considerable interest in the physics of liquid metals as well as liquid alloys. Numerous attempts [l to 31 have been made for the study of the structure and dynamics of these systems at their respective melting temperatures. Molecular dynamics is a recent approach to study the atomic motions in these alloys and metals. The instantaneous structure of the liquid metals or alloys can be obtained using X-ray diffraction or neutron inelastic scattering but these techniques give only time independent information about the arrangement of atoms in these systems and hence the dynamic picture could not ') Jaipur 302004, India

Study of Phonon Eigenfrequencies in Metallic Glasses

“…Further, to know the crystalline behaviour of both these metallic glasses, calculations have been done for the longitudinal and transverse phonon eigenfrequencies using the theory of phonons in amorphous solids (3, (6) as developed by Takeno and Goda [17] and the model approach (7), (8) the model approach of Bhatia and Singh [18] have been obtained using the computed values of elastic constants for both these glasses which are reported in Table 1. Wave-vector dependent frequencies of longitudinal and transverse phonon modes for Ni50Zr50 and Cu,,Ti,, metallic glasses have been plotted in Fig.…”

“…where n, is the total number of electrons in the system. In (7), G(qr,) is defined as the "shape factor" and is considered in order to take into account the cancellation effects which occur between kinetic and potential energies inside the core of the ions making the effective potential weak in the core. Then, where r, (= 3/47c~,,,)'~~ is the radius of the Wigner-Seitz sphere.…”

The Variational Calculation of Bulk Moduli for Liquid Binary Alloys of Alkali Metals

“…The results obtained for Na-K, Na-Cs, and K-Rb equiatomic alloys at T = 373 K are summarized in Table II in comparison with experimental data [23,24] and other theoretical results obtained by the HS variational method [3][4][5] and by methods of the dynamic theory of liquids [25,26].…”

“…The following pseudopotentials are used in aforementioned theoretical works: the Harrison first-principles pseudopotential [27] extended to binary alloys [28,29] in [3]; the non-local MP of Wang et al [30] with higherorder terms of the pseudopotential perturbation theory in [4]; the local MP of Heine and Abarenkov [31] in [5]; the local MP of Ashcroft [32] in [25] and the firstprinciples pseudopotential of Troullier and Martin [33] in [26]. The difference between our result and experiment is 3% for Na-K, 10% for K-Rb and 20% for Na-Cs.…”

A Theoretical and Computational Study of Structure‐Property Relationship in Five Binary Liquid Alloys

“…[3][4][5][6][7][8][9][10] Debye temperature, velocity of sound, and isothermal compressibility are important thermo physical properties of materials and their better understanding provides an advancement in material engineering and technology as it describes many physical phenomena of solid-state materials also. [11][12][13] The computation of Debye temperature, Θ D for binary liquid alloys through potential parameters of their pure components is not generalized and hence a challenging task in condensed matter research. [14] Recently, growing attention has been paid to determining it for different materials because it offers a simple but very effective method to describe the phonon contribution to the Gibbs energy of systems.…”