Predicting Elemental Boiling Points from First Principles

The normal boiling point (NBP) is a fundamental property of liquids and marks the intersection of the Gibb’s free energies of the liquid and the gas phase at ambient pressure. In this work, we present the first comprehensive demonstration of an approach to calculate the boiling point of atomic liquids from first-principles molecular-dynamics simulations. To this end, we combine thermodynamic integration (TDI) and perturbation theory (TPT) with a density-functional theory (DFT) Hamiltonian to deliver converged absolute liquid free energies and entropies. Linear extrapolation to the intersection with the gas phase provides NBPs, which are corrected for systematic over- or under-binding of the DFT Hamiltonian, thereby eliminating any strong dependency on the density functional. Through fine-tuning of the TDI, we reduced the walltime from weeks to about a day per element (10 − 20k core-hours), which enables extensive testing for B, Al, Na, K, Ca, Sr, Ba, Mn, Cu, Xe and Hg. This demonstrates the excellent performance and particular robustness of the approach. With a mean absolute deviation (MAD) of less than 2% from experimental references, and very similar accuracy for liquid entropies (MAD 2.3 J/(mol*K), 2% relative), the overall deviation is several times smaller than the variation between literature values for several elements.