Density Functional Computations and Molecular Dynamics Simulations of the Triethylammonium Triflate Protic Ionic...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Recent experiments revealed two first-order transitions in triethylammonium triflate ([TEA][Tf]) at approximately 230 K and 310 K.
• These transitions, along with unexplained subdiffusive proton motion, prompted further investigation.

Purpose of the Study:

• To elucidate the nature of the experimental phase transitions in [TEA][Tf] using molecular dynamics simulations.
• To analyze various properties including self-diffusion, electrical conductivity, rotational relaxation, and hydrogen-bond dynamics across a wide temperature range (200 K–400 K).

Main Methods:

• Systematic molecular dynamics simulations employing an empirical force field.
• Analysis of properties such as ion dynamics, rotational relaxation, and hydrogen bonding.
• Density functional computations were also utilized.

Main Results:

• Simulations identified a weakly discontinuous transition at 310 K, consistent with melting.
• An anomaly at 260 K in ion rotational relaxation was observed, identified as the simulation analogue of the experimental 230 K transition.
• The lower-temperature transition corresponds to a crystal to plastic phase transformation (260 K–310 K), where molecular rotation occurs without diffusion.

Conclusions:

• The simulations successfully identified the nature of the experimental transitions in [TEA][Tf].
• Molecular rotations were confirmed to be responsible for the observed subdiffusive proton motion at intermediate temperatures.
• The study also discussed ion clustering and the impact of water contamination.