In-depth explorations on the microstructural, thermodynamic and kinetic characteristics of MgCl2-KCl eutectic salt

Development of Deep Potentials of Molten MgCl2–NaCl and MgCl2–KCl Salts Driven by Machine Learning

“…As shown in Figure and Table S2, the first peak position varies little with temperature, which means the intermolecular distance is insensitive to temperature . The nearest neighbor distances ( d ) of Na–Cl (2.76 Å), K–Cl (3.10 Å) and Mg–Cl (MN: 2.37 Å and MK: 2.34 Å) pairs agree well with FPMD simulations of d Na–Cl = 2.71, d K–Cl = 3.08, and d Mg–Cl = 2.36 Å (MN) and 2.34 Å (MK) at about 870 K as well as d K–Cl = 3.09 Å and d Mg–Cl = 2.34 Å in molten MK at 1000 K, respectively. ,, Besides, the average first peak positions of Mg–Mg and Cl–Cl almost coincide with molten MN ( d Mg–Mg = 3.72 and d Cl–Cl = 3.64 Å) and MK ( d Mg–Mg = 3.74 Å and d Cl–Cl = 3.79 Å), and such small separations between d Mg–Mg and d Cl‑Cl are also observed in pure molten MgCl 2 . From Table S2, all of the d values of listed ionic pairs for molten MN are almost lower than those of MK, resulting in its constricted volume as well as larger density as displayed in Figure b.…”

“…In Figure 7, the DPMD simulated enthalpies (H) of molten MN and MK within the NPT ensemble are drawn, where the H linearly increases with temperature, and thus, the c p can be evaluated, according to the derivative of H with respect to temperature. The c p values of 1.193 J g −1 K −1 for MN and 1.284 J g −1 K −1 for MK from DPMD simulations are closer to experimental values of 1.000 J g −1 K −1 for MN and 1.013 J g −1 K −1 for MK 11,54 than previous FPMD results, 35,36 resulting from the realization of orders of magnitude extension in simulation time and size. In addition, the calculated c p for molten MK is higher than that of MN, which is consistent with the higher E bar of PMF for molten MK as discussed above.…”

“…Table 2 summarizes all viscosities of molten MN and MK obtained from DPMD and FPMD simulations and experiments. Both η SE MN and η SE MK from DPMD are lower than those of FPMD simulations (1.88 cP for MN and 3.68 cP for MK) at around 870 K, 35,36 and the larger FPMD viscosities may be interfered by heavy fluctuations of stress in the smaller simulation box. 61 At a lower temperature, the η GK MK of 800 K is almost the same as the experimental value of 1.95 cP.…”

“…For establishing the deep potentials (DPs) of molten MN and MK for DPMD simulations, the datasets are adopted from FPMD simulation results, and the detailed method description can refer to our previous works. , Briefly, the FPMD simulations are carried out through Vienna Ab initio Simulation Package (VASP) to obtain trajectories, energies, and associated force data based on the projector augmented wave method and the generalized gradient approximation with the Perdew–Burke–Ernzerhof exchange–correlation functional . The wave functions for valence electrons, Na (2s 1 ), Mg (3s 2 ), K (3s 2 3p 6 4s 1 ), and Cl (3s 2 3p 5 ), are expanded, where the multielectronic Mg (2p 6 3s 2 ) pseudopotential is also tested to study the possible effect of ionic polarization on structures as shown in Section S1 of the Supporting Information (SI).…”

“…Note: Experimental. 4,59,60 and b FPMD simulated35,36 viscosities. i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .…”