First principles molecular dynamics of molten NaI: structure, self-diffusion, polarization effects, and charge...

Area of Science:

• Condensed Matter Physics
• Computational Chemistry
• Materials Science

Background:

• Understanding the behavior of ionic liquids near their melting points is crucial for various applications.
• Classical molecular dynamics (MD) models often simplify interionic interactions, potentially limiting accuracy.
• First principles methods offer a more rigorous approach to simulating ionic systems.

Purpose of the Study:

• To investigate the structure and self-diffusion of molten NaI and NaCl using first principles Hellmann-Feynman molecular dynamics (HFMD).
• To compare HFMD results with classical MD simulations employing rigid-ion (RI) and shell-model (ShM) potentials.
• To analyze charge transfer effects in these molten salts.

Main Methods:

• First principles Hellmann-Feynman molecular dynamics (HFMD) simulations.
• Classical molecular dynamics (MD) with rigid-ion (RI) and shell-model (ShM) interionic potentials.
• Hirshfeld charge partitioning for charge transfer analysis.

Main Results:

• HFMD predicts structural differences in NaI compared to RI MD, particularly in cation-cation and anion-cation pair correlation functions.
• A ShM incorporating I- polarization partially reproduces HFMD structural features; including polarization for both ions leads to a more structured liquid.
• HFMD self-diffusion coefficients are higher than those from RI and ShM simulations.
• Charge transfer in molten NaI is comparable to NaCl and shows weak temperature dependence.

Conclusions:

• Polarization effects are the primary drivers of differences between RI and HFMD simulations for these ionic liquids.
• Charge transfer fluctuations have a minimal impact on the simulated properties of molten NaI and NaCl.
• HFMD provides a more accurate description of structure and dynamics in these molten salts compared to classical models.