Improvement of computer simulation models for metallic melts via quasielastic neutron scattering: A case study of liquid titanium

Abstract

A combination of quasielastic neutron scattering ͑QNS͒ and molecular-dynamics ͑MD͒ simulation is used to modify an embedded atom method ͑EAM͒ potential for Ti with respect to the description of melt properties and crystallization from the melt. In the MD simulation, the EAM model is optimized such that agreement with accurate data of self-diffusion coefficients from QNS is achieved. As a result the density and the melting temperature are in good agreement with experiment.

The measurement of self-diffusion coefficients in liquid metals with quasielastic neutron scattering

“…(4) are accurately described with the resulting self-diffusion coefficient of Eq. (5) up to q values of about 1.2Å −1 [13]. In agreement with the experimental data above about q = 1.2Å −1 deviations from the hydrodynamic behavior come into play.…”

“…In order to investigate up to which q values hydrodynamic predictions can be utilized for the analysis of the neutron scattering spectra, molecular dynamics (MD) computer simulations were performed using using an embedded atom model for Ti [13]. The results show that in liquid Ti long range atomic transport can be measured up to about 1.2Å −1 with QENS.…”

“…The understanding of atomic diffusion processes is a prerequisite for the study of liquid dynamics [4,5], nucleation and crystal growth [6][7][8], as well as vitrification [9,10]. Diffusion data serve as an input to the modeling of microstructure evolution [11,12] and are an essential benchmark to molecular dynamics (MD) simulation results [13,14]. In general, self-diffusion coefficients are related to the mean square displacement of the tagged atoms, whereas interdiffusion coefficients are related to collective transport of mass driven by differences in the chemical potential, e.g.…”

“…In the example of liquid Ge and 73 Ge isotope mixtures, the scattering contributions to the signal are discussed and it is shown that the quasielastic signal at small wavenumber q is dominated by incoherent scattering even for systems with a large ratio of coherent to incoherent scattering [28]. QENS results on liquid EPJ Web of Conferences titanium are shown in order to illustrate how accurate and precise self-diffusion coefficients can be derived from the QENS signal [13,29]. With two measurements on liquid nickel -one on a liquid droplet with 7 mm in diameter and the other one on a liquid sample in a thinwalled hollow-cylindrical Al 2 O 3 sample holder, we show that the resulting QENS line width at half width at half maximum is not altered by multiple scattering effects [26,30].…”

Atomistics of self-diffusion in liquid metals

“…Besides measurements under microgravity, quasielastic neutron scattering (QENS) [14][15][16][17][18][19] was argued to probe "the dynamics on atomic length scales and on a picosecond time scale, short enough to be undisturbed by the presence of convective flow." [18] "In order to derive the self-diffusion coefficient from QENS one has to assume that concepts developed in the framework of hydrodyanmics [20], i.e.…”