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Predicting Elemental Boiling Points from First Principles
preprintrevised on 10.09.2020, 14:15 and posted on 11.09.2020, 05:08 by Jan-Michael Mewes, Odile Smits
The normal boiling point (NBP) is a fundamental property of liquids and marks the intersection of the Gibbs energies of the liquid and the gas phase at ambient pressure.
This work provides the first comprehensive demonstration of the calculation of boiling points of atomic liquids through first-principles molecular-dynamics simulations.
To this end, thermodynamic integration (TDI) and perturbation theory (TPT) are combined with a density-functional theory (DFT) Hamiltonian, which provides absolute Gibbs energies, internal energies, and entropies of atomic liquids with an accuracy of a few meV/atom.
Linear extrapolation to the intersection with the Gibbs energy of a non-interacting gas phase eventually pins-down the NBPs. While these direct results can already be quite accurate, they are susceptible to a systematic over- or underbinding of the employed density functional. We show how the resulting errors can be strongly reduced by increasing the robustness of the method through a simple linear correction based on a high-level theoretical or experimental cohesive energy termed $\lambda$-scaling.
By carefully tuning the technical parameters, the walltime per element could be reduced from weeks to about a day (10-20k core-hours), which enabled extensive testing for B, Al, Na, K, Ca, Sr, Ba, Mn, Cu, Xe and Hg.
This comprehensive benchmark demonstrates the excellent performance and robustness of the approach with a mean absolute deviation (MAD) of less than 2% from experimental NBPs and very similar accuracy for liquid entropies (MAD 2.3 J/(mol*K), 2% relative). In some cases, the uncertainty in the predictions are several times smaller than the variation between literature values, allowing us to clear out ambiguities in the NBPs of B and Ba.