First-principles calculation of entropy for liquid metals

摘要

We demonstrate the accurate calculation of entropies and free energies for a variety of liquid metals using annextension of the two-phase thermodynamic (2PT) model based on a decomposition of the velocity autocorrelationnfunction into gas-like (hard sphere) and solid-like (harmonic) subsystems. The hard sphere model for the gas-likencomponent is shown to give systematically high entropies for liquid metals as a direct result of the unphysicalnLorentzian high-frequency tail. Using a memory function framework we derive a generally applicable velocitynautocorrelation and frequency spectrum for the diffusive component which recovers the low-frequency (long-time)nbehavior of the hard sphere model while providing for realistic short-time coherence and high-frequency tails tonthe spectrum. This approach provides a significant increase in the accuracy of the calculated entropies for liquidnmetals and is compared to ambient pressure data for liquid sodium, aluminum, gallium, tin, and iron. The usenof this method for the determination of melt boundaries is demonstrated with a calculation of the high-pressurenbcc melt boundary for sodium. With the significantly improved accuracy available with the memory functionntreatment for softer interatomic potentials, the 2PT model for entropy calculations should find broader applicationnin high energy density science, warm dense matter, planetary science, geophysics, and material science.