  The thermodynamic description of the (LiF, NaF, KF, CrF2)-CrF3 systems has
been revisited, aiming for a better understanding of the effects of Cr on the
FLiNaK molten salt. First-principles calculations based on density functional
theory (DFT) were performed to determine the electronic and structural
properties of each compound, including the formation enthalpy, volume, and bulk
modulus. DFT-based phonon calculations were carried out to determine the
thermodynamic properties of compounds, for example, enthalpy, entropy, and heat
capacity as functions of temperature. Phonon-based thermodynamic properties
show a good agreement with experimental data of binary compounds LiF, NaF, KF,
CrF3, and CrF2, establishing a solid foundation to determine thermodynamic
properties of ternary compounds as well as to verify results estimated by the
Neumann-Kopp rule. Additionally, DFT-based ab initio molecular dynamics (AIMD)
simulations were employed to predict the mixing enthalpies of liquid salts.
Using DFT-based results and experimental data in the literature, the (LiF, NaF,
KF, CrF2)-CrF3 system has been remodeled in terms of the CALculation of PHAse
Diagrams (CALPHAD) approach using the modified quasichemical model with
quadruplet approximation (MQMQA) for liquid. Calculated phase stability in the
present work shows an excellent agreement with experiments, indicating the
effectiveness of combining DFT-based total energy, phonon, and AIMD
calculations, and CALPHAD modeling to provide the thermodynamic description in
complex molten salt systems.
