Solution enthalpy calculation for impurity in liquid metal by first-principles calculations: A benchmark test for...

The solution enthalpy of oxygen in liquid Na was calculated as a test case for the computational method to evaluate the solution enthalpy in liquid metal using first-principles calculations. To obtain the necessary thermodynamic quantities at high temperatures, (i) first-principles molecular dynamics for pure and O-including liquid Na systems, (ii) vibration analysis for an O₂ molecule, and (iii) phonon-based quasi-harmonic approximation for solid Na and Na₂O were conducted. The calculation results were compared with available experimental data to validate the method. Consequently, the O₂ solution enthalpy was calculated to be -387.1 kJ/mol at 600 K and -374.0 kJ/mol at 1000 K, comparable to the experimental data of -375.7 kJ/mol at 600 K and -369.3 kJ/mol at 1000 K. The Na₂O solution enthalpy was calculated to be 28.6 kJ/mol at 600 K and 38.2 kJ/mol at 1000 K, while the experimental data gave a temperature-independent value of 46.9 kJ/mol. The possible causes of errors in the calculations were discussed. This work shows that computational calculations can contribute to establishing a fundamental database on the solubility of impurities in liquid metals.