Dispersion- and Exchange-Corrected Density Functional Theory for Sodium Ion Hydration

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Developing accurate exchange-correlation functionals in density functional theory (DFT) is crucial for describing intermolecular electron correlation and delocalization.
• Recent functionals incorporate long-range corrections for dispersion and electron exchange to address these challenges.

Purpose of the Study:

• To investigate the impact of these dual corrections on the accuracy of binding free energy predictions for sodium-water clusters.
• To compare the performance of different DFT functionals against high-level ab initio methods and experimental data.

Main Methods:

• Utilized density functional theory (DFT) with various exchange-correlation functionals, including ωB97X-D and CAM-B3LYP.
• Employed high-level ab initio methods, specifically coupled cluster with singles, doubles, and perturbative triples (CCSD(T)), as a benchmark.
• Performed binding energy decomposition analysis and assessed charge transfer and polarizability.

Main Results:

• The dual-corrected ωB97X-D functional yielded binding energies closest to CCSD(T) results for sodium-water clusters.
• ωB97X-D showed smaller pairwise ion-water interaction energies and larger multibody contributions, consistent with CCSD(T).
• The exchange-corrected CAM-B3LYP functional exhibited the best agreement with experimental binding free energies, with errors under 1 kcal/mol.

Conclusions:

• Dual corrections in DFT functionals enhance the description of intermolecular interactions in sodium-water clusters.
• While ωB97X-D aligns well with high-level theory, CAM-B3LYP's parametrization leads to superior experimental agreement for binding free energies.
• Accurate free energy calculations for larger clusters (>4 waters) necessitate considering "split-shell" coordination.