Hydration structure of Na⁺ and K⁺ from ab initio molecular dynamics based on modern density functional theory

Abstract

Molecular dynamics (Born–Oppenheimer) simulations based on density functional theory have been carried out to investigate the solvation structure of monovalent Na⁺ and K⁺ cations in water under ambient conditions. Four recently proposed van der Waals (vdW) density functionals (LMKLL, DRSLL, DRSLL-PBE, DRSLL-optB88), the semiempirical vdW method of Grimme (BLYP-D3) and conventional gradient-corrected (GGA-BLYP) density functionals are applied in order to evaluate their accuracy in describing the hydration structure of alkali metal ions. Theoretical results are compared to available experimental data. Our results indicate that addition of corrections accounting for dispersion forces significantly improves the agreement between predicted and measured coordination numbers for both Na⁺ and K⁺ cations. Analysis of radial distribution functions brings further support to the notion that the choice of the generalised gradient approximation density functional impacts crucially on the computed structural properties. DRSLL-optB88 and BLYP-D3 provide the best agreement with experiment.

Keywords:

• solvation structures
• dispersion interactions
• sodium ions
• potassium ions
• Born–Oppenheimer molecular dynamics

Acknowledgements

We thank Roberto Car, Xifan Wu and Robert DiStasio Jr. for many insightful comments. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Additional information

Funding

We used resources from Extreme Science and Engineering Discovery Environment (XSEDE) (www.xsede.org/high-performance-computing) [grant number MCA93S020] and the Temple University High-Performance Computing System purchased in part with National Science Foundation (NSF) [grant number MRI-R2 0958854]. We are grateful for partial financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, SciDAC Award DEFG02-12ER16333.