Comparative Assessment of Exchange-Correlation Functionals for the Structural, Thermodynamic, and Transport Properties of Liquid Lithium

Abstract

Liquid lithium (Li) is an important material for advanced energy applications, particularly fusion energy systems, where it can serve as a tritium breeder, coolant, and plasma-facing material. The development of these technologies requires accurate predictions of liquid-state properties over a wide range of temperatures and operating conditions, making reliable first-principles simulations increasingly important. However, the performance and relative accuracy of commonly used density functional theory (DFT) exchange-correlation (XC) functionals for liquid Li have not been systematically benchmarked against experiment. In this work, we use ab initio molecular dynamics (AIMD) simulations to evaluate structural, thermodynamic, and transport properties of liquid Li. Structural properties probe local atomic ordering, thermodynamic properties, including density, bulk modulus, thermal expansion coefficient, and heat capacity, probe the liquid equation of state and thermal response, and self-diffusion probes atomic dynamics. Ten XC functionals are benchmarked, including local-density approximation (LDA), generalized gradient approximation (GGA), and zero-damping D3-corrected [D3(0)] functionals, and the results are systematically compared with available experimental data. The results show that the choice of XC functional has a significant impact on the predicted properties. At 1000 K, revPBE predicts an equilibrium volume of 25.00 Å3 per atom, compared with the experimental value of 25.09 Å3 per atom, whereas PBE-D3 predicts 22.06 Å3 per atom. The tested D3-corrected functionals generally predict smaller equilibrium volumes, higher densities and bulk moduli, and lower thermal expansion coefficients than experiment, indicating excessive binding within the tested D3-corrected framework. Among the functionals considered, revPBE provides the most balanced overall agreement with experiment, including a thermal expansion coefficient of 2.75 × 10–4 K–1 ± 8.24 × 10–6 K–1, compared with the experimental value of 2.77 × 10–4 ± 7.18 × 10–6 K–1, and a self-diffusion activation energy of 9.42 ± 2.03 kJmol–1, compared with 9.62 ± 1.26 kJmol–1. These results provide guidance for selecting experimentally anchored XC functionals for accurate AIMD modeling of liquid Li.