Figure shows a comparison of the total number of ligands and the number of Cl -ligands in the first coordination shell. With increasing temperature, the static dielectric constant of water decreases, which promotes ion association. This effect is seen in PIM where an increase of about one Cl -ion is observed from subcritical to supercritical conditions, consistent with AIMD data , EXAFS studies , XAS studies and HKF model data . N-POL MD predicts higher Cl -coordination and negligible change with temperature. In terms of the absolute number of Cl - ligands, the PIM data agrees well with the HKF model generated using solubility data from Migdisov et al. and EXAFS data , whereas an overestimation of about one ligand is observed for N-POL MD. With decreasing temperature, PIM shows an increase in the total number of ligands of about one, in agreement with EXAFS data . XAS data predict an increase of about three ligands. However, XAS generally overestimates coordination numbers indicated by the 10-fold coordinated La 3+ predicted at subcritical conditions . N-POL MD predicts negligible change in the total number of ligands with temperature. In terms of the absolute number of ligands in the first coordination shell, PIM data agree well with EXAFS and AIMD data, while N-POL MD overestimates the number of ligands by about one. PIM also shows better agreement with XAS studies in terms of the total number of ligands compared to N-POL MD at 773 K. In general, La-O distances predicted by PIM are shorter than those in AIMD and experiments at similar conditions. In general, association constants predicted by AIMD, N-POL MD and PIM follow the order, log K ∞ eq,N -P OL > log K ∞ eq,P IM > log K ∞ eq,AIM D . This is seen in Table and also illustrated in Figure . Although PIM gives better log K ∞ eq values as compared to N-POL, the disagreement with AIMD is still relatively large, i.e. about one log unit in some cases. Table shows the cumulative association constants, log β obtained from N-POL MD, PIM, AIMD and the HKF model parameterized with solubility data from Migdisov et al. up to ∼350 • C. They are obtained by cumulative addition of log K ∞ eq values shown in Table and, hence, follow the same descending order as association constants. log β predicted by PIM for reactions 2 and 3 at 473 K are in better agreement with the thermodynamic model and AIMD than N-POL MD. Both models predict an increase in log β values of LaCl 2+ and LaCl + 2 with increasing temperature, in agreement with data from the HKF model up to ∼400 • C and with AIMD data . Due to the increased stability of La-Cl complexes at higher temperatures, the stepwise addition of Cl -into the coordination sphere of La 3+ becomes more exothermic at higher temperatures. conditions. Absolute values of ∆G 2-1 from PIM are generally lower than those from AIMD.