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First-principles calculation of entropy for liquid metals
1Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|February 4, 2014
Summary
We improved the two-phase thermodynamic (2PT) model for calculating liquid metal entropies. Our new method uses a memory function to accurately model the velocity autocorrelation, enhancing predictions for materials science applications.
Area of Science:
- Thermodynamics
- Materials Science
- Computational Physics
Background:
- Accurate calculation of thermodynamic properties like entropy is crucial for understanding liquid metals.
- The standard two-phase thermodynamic (2PT) model, while useful, overestimates entropy in liquid metals due to its hard sphere component's unphysical high-frequency tail.
Purpose of the Study:
- To develop a more accurate method for calculating entropies and free energies of liquid metals.
- To refine the two-phase thermodynamic (2PT) model by addressing limitations in its treatment of the velocity autocorrelation function.
Main Methods:
- Extended the two-phase thermodynamic (2PT) model by decomposing the velocity autocorrelation function into gas-like and solid-like subsystems.
- Employed a memory function framework to derive a generally applicable velocity autocorrelation and frequency spectrum for the diffusive component.
- Compared calculated entropies with ambient pressure data for liquid sodium, aluminum, gallium, tin, and iron.
Main Results:
- The refined model provides systematically high entropies for liquid metals, correcting the overestimation from the standard hard sphere model.
- The derived memory function approach accurately captures short-time coherence and realistic high-frequency spectrum tails.
- Demonstrated the method's utility by calculating the high-pressure bcc melt boundary for sodium.
Conclusions:
- The enhanced 2PT model with memory functions significantly increases the accuracy of entropy calculations for liquid metals.
- This improved accuracy, especially for softer interatomic potentials, broadens the applicability of the 2PT model.
- The method is well-suited for applications in high energy density science, warm dense matter, planetary science, geophysics, and material science.
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