Structure factors and phonon dispersion in liquid Li 0.61 Na 0.39 alloy (original) (raw)
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On the dynamical properties of the liquid Li–Na alloy
Journal of Non-Crystalline Solids, 1999
Several dynamical properties of the liquid Li±Na alloy have been studied by both molecular dynamics simulations and by a theoretical memory function formalism. We present results for the Li 0X61 Na 0X39 system where comparison is performed with the experimental inelastic neutron scattering data. The obtained results for the partial dynamic structure factors reveal the existence of propagating sound modes for wavevectors k`1.4 # A À1 . Ó 0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 -3 0 9 3 ( 9 9 ) 0 0 2 6 2 -8
BIBECHANA
Along with a few elastic constants, a recently created pseudopotential is employed to examine the vibrational properties of some simple alkali metals, i.e. Li, Na, K, Rb and Cs. The phonon dispersion curves (PDC) are computed in the text. (ωL and ωT), longitudinal sound velocity (vl), transverse sound velocity (vt), isothermal bulk modulus (B), modulus of rigidity (G), Young’s modulus (Y ), Debye temperature (θD) of some liquid alkali metals. The second order technique used in the current work, using Hubbard and Beeby (HB) equations, is based on pseudopotential theory. The various Percus-Yevick hard sphere (PYHS) and one-component plasma (OCP) structure factors used in the current investigation are used to construct the pair correlation function g(r). The current paper makes use of three distinct forms of local field correction functions developed by Hartree (H), Taylor (T), and Nagy (N). The current findings are found to qualitatively agree with the experimental and theoretical dat...
Journal of Physics: Condensed Matter, 2004
Neutron diffraction experiments, made at a steady-state reactor source, were used to study the structure of liquid 7 Li at temperatures of 197, 452 and 595 • C. A careful data analysis procedure was undertaken in which specific issues taken into account include (i) the influence of Brillouin modes on the measured diffraction pattern at small scattering vectors, (ii) inelasticity corrections that are significant for light atom systems, such as lithium, and (iii) the effects caused by the diffractometer resolution function. Data sets taken for the same liquid temperature using different incident neutron energies yield ion-ion partial structure factors, S II (k), that are in agreement within the statistical errors. The S II (k) are compared with previous experimental results and with the results obtained from liquid state theory and molecular dynamics methods made using several different local pseudopotentials. Finally, the valence electron form factor, ρ(k), is estimated by combining S II (k) with x-ray diffraction data and the ion-valence electron partial structure factor, S Ie (k), is calculated by combining S II (k) with the ρ(k) obtained from both experiment and theory. The results show that the extraction of ρ(k) and S Ie (k) by a combination of neutron and x-ray diffraction methods is feasible in practice, but demonstrates a need for new x-ray diffraction experiments on liquid lithium.
Phonon Dispersion Curves of Liquid Metals
2010
In the present paper, the phonon dispersion curves (PDC) of some alkali metals are reported in second order approach through the equation given by Hubbard and Beeby (HB). The pair correlation function is directly computed from the interatomic pair potential, which is used in the present computation. Two different forms of local field correction functions proposed by Hartree (H) and Ichimaru-Utsumi (IU) are used in the present study the screening dependence of the phonon frequencies in the metallic elements. Present results of phonon dispersion curves are found to be in qualitative agreement with available experimental results.
Static structure and dynamics of the liquid Li-Na and Li-Mg alloys
Physical Review E, 1998
We present calculations for the static structure and ordering properties of two lithium-based s-p bonded liquid alloys, Li-Na and Li-Mg. Our theoretical approach is based on the neutral pseudoatom method to derive the interatomic pair potentials, and on the modified-hypernetted-chain theory of liquids to obtain the liquid static structure, leading to a whole combination that is free of adjustable parameters. The study is complemented by performing molecular dynamics simulations which, besides checking the theoretical static structural results, also allow a calculation of some dynamical properties. The obtained results are compared with the available experimental data. ͓S1063-651X͑98͒07110-4͔
A study of the electronic properties of liquid alkali metals: a self-consistent approach
Brazilian Journal of Physics, 2003
We study the electronic properties (density of states, conductivity and thermopower) of some nearly-free-electron systems: the liquid alkali metals and two liquid alloys, Li-Na and Na-K. The study has been performed within the selfconsistent second order Renormalized Propagator Perturbation Expansion (RPE) for the self-energy. The input ionic pseudopotentials and static correlation functions are derived from the neutral pseudoatom method and the modified hypernetted chain theory of liquids, respectively. Reasonable agreement with experiment is found for Na, K, Rb and Na-K, whereas for Li and Cs and Li-Na the agreement is less satisfactory Submitted to: Braz. J. Phys.
On the structure of liquid alkali metals
Journal of Physics F: Metal Physics
We calculate a structure factor for the liquid alkali metals assuming that the soft core of the potential plays the dcminant structure-determining role. The structure factor is calculated in an analytic form suitable for fitting to experimental data. We obtain good agreement with existing measurements on Na. K and Rb. The relationship between the interatomic potential and the static structure factor, S(q), of liquid metals is still a subject of interest. While it is now generally accepted that a unique pair potential cannot be deduced from a measured structure factor, debate continues over which features of the potential are most influential in determining the form of S(q). Discussion (see e.g. Ailawadi 1980 and references therein) has mostly centred around the relative roles of soft and hard cores in the effective ion-ion potential, VeR(r), in simple (s-p bonded) liquid metals, and whether or not an attractive minimum is needed. The well known early success of the hard-core potential (Ashcroft and Lekner 1966) in accounting for much of the structure in S(q) has been replaced by emphasis on the importance of a soft core (see e.g. Hoshino 1980). Recently, however, claims by Cummings and Egelstaff (1982, to be referred to as CE) that Friedel oscillations can account for the observed properties of S(q) in liquid Rb have again clouded the issue, particularly since the form of effective ion-ion potential used in their study does not mimic well the physical characteristics of Friedel oscillations. In this letter we present results which strongiy support the view that the part of V,&) which has most influence in determining S(q) is the soft core. Furthermore, we are able to account for the density derivative of S(q) without recourse to the density-dependent potential parameters required in the analysis of CE. We suggest that the work of the latter authors may be interpreted in ti way which does not involve an important role for Friedel oscillations. The general features exhibited by effective ion-ion potentials in liquid metals are well known (Kumaravadivel and Evans 1976, Ailawadi 1980, Hafner 1980): a more or less hard-core repulsion, perhaps (but not necessarily) a weak attractive well at a distance corresponding approximately to the interatomic spacing in the solid phase, and long-range Friedel oscillations. The first of these properties led Ashcroft and Lekner (1966) to postulate that S(q) for a liquid metal could be described by the Percus-Yevick hard-sphere model. This idea met with tolerable success when the hard-core radius was considered as a parameter to be fitted to the measured static structure factor s. The next step was to try to include attractive interactions by perturbative methods (Ailawadi 1980
Dynamics of Liquid Lithium Atoms. Pseudopotential and EAM-Type Potentials
Journal of Experimental and Theoretical Physics, 2018
It is generally accepted that the complicated character of the interparticle interaction in liquid metals is reproduced most correctly by many-particle potentials of the EAM-type (embedded atom model) interparticle interaction. It is shown that in the case of liquid lithium near the melting temperature (T m = 453.65 K), the spherical pseudopotential provides a better agreement with experimental data on elastic and inelastic X-ray scattering as compared to the known EAM potentials. The calculations of the dynamic structural factor and spectral densities of the longitudinal and transverse atomic currents lead to the conclusion that although the pseudopotential and EAM potentials generate a certain qualitative correspondence in the features of collective dynamics, the interparticle interaction of the spherical type reproduces correctly the general form of the dynamic structure factor in a certain wavenumber range, as well as the dispersion relation for collective excitations.
Phonon Dispersion in Equiatomic Binary Alloys
2009
The computations of the phonon dispersion curves (PDC) of four equiatomic K based binary alloys viz. K0.5Li0.5, K0.5Na0.5, K0.5Rb0.5 and K0.5Cs0.5 to second order in local model potential is discussed in terms of real-space sum of Born von Karman central force constants. Instead of the concentration average of the force constants of metallic Li, Na, K, Rb and Cs, the pseudo-alloy-atom (PAA) is adopted to compute directly the force constants of four equiatomic K-based binary alloys. The exchange and correlation functions due to Hartree (H) and Ichimaru-Utsumi (IU) are used to investigate influence of screening effects. The phonon frequencies of four equiatomic K-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. While, the frequencies in the longitudinal branch are suppressed due to IU-screening function than the frequencies due to static H-screening function. The A1-XBX (A=K; B=Li, Na,...