Mass transport and thermal properties of liquid (melting to boiling point) tungsten: a molecular dynamics simulations

We present molecular dynamics simulation to obtain melting point, structural and atomic transport properties of liquid tungsten. We considered the second-neighbor extended Finnis-Sinclair (EFS) potential as an effective interaction. We find melting temperature (T-M) and density in agreement with the reported values. EFS potential gives accurate information for structure factor S(q), pair correlation function g(r), and transport coefficients like self-diffusion coefficient and viscosity upto similar to 1.5T(M). Large viscosity proposes the rheological nature of liquid W. The self-diffusion coefficient follows the Arrhenius law giving the activation energy 1.22 eV. We find 'shoulder' in the second peak of S(q), which disappears with temperatures. This characteristic is attributed to the high density and clustering of W-atoms at the near-neighbor distance. The asymmetric first peak in g(r) and shoulder in S(q) proposes that the liquid W exhibits non-normal metallic behaviour. Discrepancy observed in caloric properties for temperature >6000 K is also discussed. We propose that the 'softness' and broad dip in EFS potential are responsible for these discrepancies, and necessitate the inclusion of angular forces. The single particle correlation is discussed in terms of the velocity autocorrelation function and the long-wavelength limit of S(q) is utilized to derive adiabatic sound velocity in confirmation with reported results.