The new PIM interaction potential gives good estimates of La-Cl and La-O distances at the studied conditions. PIM provides better estimates of total coordination and Cl -coordination numbers compared to N-POL MD in dilute solutions. It also reproduces the increase in La-Cl coordination with increasing temperature as observed in experiments. However, the La-O distances predicted by PIM are shorter than the experimental data at similar conditions. Calculation of association constants reveal increasing stability of LaCl 2+ and LaCl + 2 complexes with increasing temperature. In general, the formation constants calculated from PIM simulations are closer to the data from the AIMD and HKF models than those from N-POL MD. This is despite the fact that no energy values are used in fitting the PIM. Relative stabilities of CIPs and SShIPs predicted by PIM are in agreement with AIMD at both conditions. Altogether, the newly fitted PIM gives more precise structural and thermodynamic insight into dilute La-Cl-bearing hydrothermal fluids at both the studied temperature and pressure conditions than those from simple pair potentials, with reasonable computational cost. We also show that the effects of simulation box size on calculated thermodynamics properties are negligibly small at high temperatures. Our results underpin the importance of an explicit description of ionic polarizability to retrieve reliable structural and thermodynamic information in hydrothermal systems containing highly polarizable anions such as Cl -and cations with high polarization power such as La 3+ .