Structural and dynamical properties of liquid ${\mathrm{Cu}}_{80}{\mathrm{Si}}_{20}$ alloy studied experimentally and by $\mathit{ab}\hspace{0.5em}\mathit{initio}$ molecular dynamics simulations

The local structures and dynamical properties of the liquid Cu${}_{80}$Si${}_{20}$ alloy have been studied by x-ray diffraction and ab initio molecular dynamics (MD) simulations. The pair-correlation functions and the structure factors derived from the three-dimensional coordinates of the MD configurations agree well with the experimental results. The local structure of the liquids is analyzed using Honeycutt-Andersen (HA) indices, Voronoi tessellation (VT), and an atomic cluster-alignment method. The HA indices analysis shows that the pentagonal bipyramid, a fragment of an icosahedron (ICO), plays a dominant role in the short-range order (SRO) of the Cu${}_{80}$Si${}_{20}$ liquid. The HA indices corresponding to the pentagonal bipyramid increase dramatically with decreasing temperature. VT analysis indicates that, while the liquid does exhibit a strong icosahedral SRO, fcc-like SRO is also measurable. The results from VT analysis are further confirmed using the recently developed atomic cluster-alignment method. Finally, self-diffusion constants, as a function of temperature for both Cu and Si species, are calculated.

Figure 1

Comparison the total pair-correlation functions between measurement and simulation and the calculated partial pair-correlation functions of the liquid Cu${}_{80}$Si${}_{20}$ alloy at different temperatures.

Figure 2

The average and partial CNs of the liquid Cu${}_{80}$Si${}_{20}$ alloy.

Figure 3

Calculated partial bond-angle distribution functions of the liquid Cu${}_{80}$Si${}_{20}$ alloy. (a) Cu-Cu-Cu, (b) Cu-Si-Cu, (c) Cu-Si-Si, (d) Cu-Cu-Si, (e) Si-Cu-Si, and (f) Si-Si-Si.

Figure 4

The top four most populated HA indices in the liquid Cu${}_{80}$Si${}_{20}$ alloy as a function of temperature.

Figure 5

The result of the VT analysis of the liquid Cu${}_{80}$Si${}_{20}$ alloy. The clusters and Voronoi cells are given in the right panel, (a) ICO-like, (b) fcc-like, and (c) unclassified.

Figure 6

The collective alignment results for Cu${}_{80}$Si${}_{20}$ at different temperatures. Clusters in the upper panel represent the Cu-centered (blue) ones, and those in the lower panel stand for the Si-centered (yellow) ones. The isovalue is set to be 0.42 Å${}^{-3}$.

Figure 7

Population analysis by using the individual cluster-template alignment. (a) Population of ISROs in the whole system in Cu-centered clusters and Si-centered clusters, respectively. (b) Population of fcc SROs in the whole system in Cu-centered clusters and Si-centered clusters, respectively. The populations are normalized to the corresponding number of atoms (i.e., 100 for total, 80 for Cu centered, and 20 for Si centered) in the system, respectively.

Figure 8

The MSD and self-diffusion coefficient of Cu${}_{80}$Si${}_{20}$ at different temperatures.The red lines are the fitting lines.