Estimation of component activities of ternary liquid alloys by partial radial distribution functions of binary liquid alloys obtained from ab initio molecular dynamics simulation

The key binary parameters of solution thermodynamic models are usually determined by the measured activity data of binary solutions, and then thermodynamic properties of the relevant ternary or even multi-component solutions can be predicted. However, in the absence of experimental data, it is currently still difficult and challenging to determine these parameters reliably. In this paper, the partial radial distribution functions (PRDF) of 9 binary liquid alloys are obtained by ab initio molecular dynamics (AIMD) simulation. Based on the statistical average principle of physical quantities, a simplified expression of the average pair potential energy (APPE) of fluid molecules with PRDF is correctly derived. Then it can be correlated with the binary model parameters of the Regular Solution Model (RSM), the Wilson equation, the Non-Random Two-Liquid equation (NRTL), and the Molecular Interaction Volume Model (MIVM), and their values are determined. Based on this, the component activities of the 9 binary as well as the 4 ternary liquid alloys systems were estimated and compared with those obtained by the fitting parameter method and the Miedema model. The results show that for the 9 binary alloys systems, when the symmetric PRDF method is used, the standard deviation (SD) and the average relative deviation (ARD) of Wilson equation are 0.073 and 25 % respectively; when the asymmetric PRDF method is used, the SD and ARD of RSM are 0.067 and 15 %; when the fitting parameter method is used, the SD and ARD of Wilson equation are 0.016 and 4 %; when the Miedema model is used, its SD and ARD are 0.090 and 35 %, respectively. For the 4 ternary alloys systems, when the symmetric method is used, the SD and ARD of Wilson equation are 0.068 and 16 % respectively; when the asymmetric method is used, the SD and ARD of RSM are 0.061 and 14 %; when the fitting parameter method is used, the SD and ARD of MIVM are 0.028 and 6 %; when the combined method of the Miedema model and the Toop model is used, its SD and ARD are 0.052 and 13 %, respectively. This indicates that the simplified expression of APPE related with PRDF can be used to obtain the key binary parameters of some thermodynamic models for estimating all component activities of ternary or even multi-component liquid alloys in the absence of activity experimental data of binary liquid alloys.