Pressure-induced effects in the spectra of collective excitations in pure liquid metals

Abstract

Collective dynamics of metallic melts at high pressures is one of the open issues of condensed matter physics. By means of ab initio molecular dynamics simulations, we examine features of dispersions of collective excitations through transverse current spectral functions, as a function of pressure. Typical metallic melts, such as Li and Na monovalent metals as well as Al, Pb and In polyvalent metals are considered. We firmly establish the emergence of a second branch of high-frequency transverse modes with pressure in these metals, that we associate with the pronounced high-frequency shoulder in the vibrational density of states. Similar correlation also exist with the low frequency modes. The origin of the pressure-induced evolution of transverse excitations in liquid metals is discussed.

Properties of bulk liquid Pd and Pt and their free liquid surface studied with first principles techniques

“…As for the Z(ω), we observe a single peak followed by a weak shoulder which is more marked for l-Pt. We mention that the ab-initio study of l-Tl [35] also found a similar structure for the corresponding Z(ω), although the shoulder was more marked. Moreover, they suggested a correlation between the appearance of a high frequency shoulder/peak in the Z(ω) and the emergence of a second high-frequency transverse branch with practically the same frequency as that of the peak/shoulder.…”

“…For both metals, we have found two branches with the high-frequency branch existing over a limited q-range around the position of the main peak of the S(q). To our knowledge, the emergence of a second, high-frequency, transverse branch has been found in high pressure l-Li, l-Na, l-Fe, l-Pb and l-Al [31,32,33,34], but recently some AIMD studies at ambient pressure have also unveiled a second high-frequency transverse branch, in particular for l-Ni, l-Tl, l-Zn and l-Sn near melting [7,35,36,37]. In all cases, this new branch appears for q-values greater than the first pseudo-Brillouin zone boundary, i.e.…”

Structure and dynamics of the liquid 3d transition metals near melting. An ab initio study

“…The inset in figure 4 represents the associated power spectrum, Z(ω), and we find that its shape may display a double peak (l-V and l-Co), a peak followed by a shoulder (l-Cr, l-Sc and l-Ni) or just one peak (l-Mn). We notice that in a recent ab-initio study of l-Tl [19], where the associated Z(ω) showed a peak followed by a marked shoulder, the authors pointed to some correlation between the appearance of a high frequency shoulder/peak and the emergence of a second high-frequency transverse branch with practically the same frequency as that of the peak/shoulder. We will analyze this point in the following section where the dispersion relation for the transverse current has been calculated.…”

“…Our previous study of l-Ti, l-Fe and l-Ni devoted particular attention to the investigation of their collective dynamic properties. This was prompted by the recent finding [19,20,21] of some unusual dynamical features such as transverse low-energy excitations in the dynamic strucure factor and/or the appearance of a second, high-frequency peak, in the transverse current spectral functions. Still, we lack an understanding of the dynamical processes behind the emergence of the those features.…”

Future applications of the high-flux thermal neutron spectroscopy: the ever-green case of collective excitations in liquid metals

“…The Generalized Collective Modes (GCM) method [108,109] is a widely applied theoretical approach to the investigation of collective modes in liquids and an effective framework to analyse the transverse excitations spectra in liquids [110][111][112][113], binary mixtures [114,115] and glasses [116]. Also, the recent extensive molecular dynamics simulation work of Del Rio et al on liquid metals contribute to shed light on the interpretation of the vibrational spectra and the complex behaviour of collective modes in these systems [117][118][119].…”