Electronic structure calculations in electrolyte solutions: Methods for neutralization of extended charged interfaces

Area of Science:

• Computational materials science
• Physical chemistry
• Condensed matter physics

Background:

• Density functional theory (DFT) with periodic boundary conditions (PBCs) is crucial for simulating extended materials.
• Standard methods impose artificial electroneutrality using a uniform background charge (jellium), which doesn't reflect real-world screening mechanisms.
• Electrolyte screening in systems like charged electrodes is a more realistic neutralization process.

Purpose of the Study:

• To develop a physically optimal method for imposing electroneutrality in DFT simulations of charged materials within PBCs.
• To accurately model the screening effect of surrounding electrolytes, mimicking experimental conditions.
• To implement and compare new neutralization schemes within a linear-scaling DFT code.

Main Methods:

• Hybrid quantum-continuum modeling using a modified Poisson-Boltzmann equation.
• Introducing the Neutralization by Electrolyte Concentration Shift (NECS) principle, minimizing electrolyte ion concentration deviations from open boundary conditions (OBCs).
• Implementation in the ONETEP DFT code with a parallel Poisson-Boltzmann solver (DL_MG).
• Development of a simplified 'accessible jellium' neutralization scheme.

Main Results:

• The NECS approach ensures simultaneous electroneutrality in the simulation cell and bulk electrolyte, matching experimental observations.
• NECS accurately reproduces electrolyte ion concentration profiles, unlike traditional jellium methods.
• Demonstration and comparison of NECS and 'accessible jellium' on various examples.

Conclusions:

• NECS provides a physically grounded and accurate method for handling charged systems in DFT simulations under PBCs.
• This method bridges the gap between theoretical simulations and experimental observations of electrolyte-influenced materials.
• The developed schemes enhance the capability of DFT codes like ONETEP for simulating complex electrochemical interfaces.