Modeling Nuclear Quantum Effects on Long Range Electrostatics in Nonuniform Fluids

Nuclear quantum effects play critical roles in a variety of molecular processes, especially in systems that contain hydrogen and other light nuclei, such as water. For water at ambient conditions, nuclear quantum effects are often interpreted as local effects resulting from a smearing of the hydrogen atom distribution. However, the orientational structure of water at interfaces determines long range effects like electrostatics through the O-H bond ordering that is impacted by nuclear quantum effects. In this work, I examine nuclear quantum effects on long range electrostatics of water confined between hydrophobic walls using path integral simulations. To do so, I combine concepts from local molecular field (LMF) theory with path integral methods at varying levels of approximation to develop an efficient and physically intuitive approaches for describing long range electrostatics in nonuniform quantum systems. Using these approaches, I show that quantum water requires larger electrostatic forces to achieve the same level of interfacial screening as the corresponding classical system. This work highlights subtleties of electrostatics in nonuniform classical and quantum molecular systems, and the methods presented here are expected to be of use to efficiently model nuclear quantum effects in large systems.Comment: 11 pages, 4 figure

Electronic paddle-wheels in a solid-state electrolyte

Solid-state superionic conductors (SSICs) are promising alternatives to liquid electrolytes in batteries and other energy storage technologies. The rational design of SSICs and ultimately their deployment in battery technologies is hindered by the lack of a thorough understanding of their ion conduction mechanisms. In SSICs containing molecular ions, rotational dynamics couple to translational diffusion to create a 'paddle-wheel' effect that facilitates conduction. The paddle-wheel mechanism explains many important features of molecular SSICs, but an explanation for ion conduction and anharmonic lattice dynamics in SSICs composed of monatomic ions is still needed. We predict that ion conduction in the classic SSIC AgI involves 'electronic paddle-wheels,' rotational motion of lone pairs that couple to and facilitate ion diffusion. The electronic paddle-wheel mechanism creates a universal perspective for understanding ion conductivity in both monatomic and molecular SSICs that will create design principles for engineering solid-state electrolytes from the electronic level up to the macroscale.Comment: 6 pages, 3 figure