A systematic study of chloride ion solvation in water using van der Waals inclusive hybrid density functional theory

Abstract

In this work, the solvation and electronic structure of the aqueous chloride ion solution was investigated using density functional theory (DFT) based ab initio molecular dynamics (AIMD). From an analysis of radial distribution functions, coordination numbers, and solvation structures, we found that exact exchange (E _xx) and non-local van der Waals (vdW) interactions effectively weaken the interactions between the Cl⁻ ion and the first solvation shell. With a Cl–O coordination number in excellent agreement with experiment, we found that most configurations generated with vdW-inclusive hybrid DFT exhibit sixfold coordinated distorted trigonal prism structures, which is indicative of a significantly disordered first solvation shell. By performing a series of band structure calculations on configurations generated from AIMD simulations with varying DFT potentials, we found that the solvated ion orbital energy levels (unlike the band structure of liquid water) strongly depend on the underlying molecular structures. In addition, these orbital energy levels were also significantly affected by the DFT functional employed for the electronic structure; as the fraction of E _xx was increased, the gap between the highest occupied molecular orbital of Cl⁻ and the valence band maximum of liquid water steadily increased towards the experimental value.

Keywords:

• chloride ion
• solvation structures
• coordination number
• exact exchange
• van der Waals forces

Acknowledgements

A. Bankura and M. Klein are grateful for partial financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, SciDAC Award DE-FG02-12ER16333 and computational support from XSEDE grant no. MCA93S020. X. Wu acknowledges support from the American Chemical Society Petroleum Research Fund (ACS PRF) under grant no. 53482-DNI6. R. DiStasio and B. Santra acknowledge support from the Scientific Discovery through Advanced Computing (SciDAC) programme through the Department of Energy (DOE) under grant nos. DE-SC0005180 and DE-SC0008626. 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. This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under contract DE-AC02-06CH11357.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

A. Bankura and M. Klein: U.S. Department of Energy, Office of Basic Energy Sciences, SciDAC Award DE-FG02-12ER16333, XSEDE [grant number MCA93S020]. X. Wu: American Chemical Society Petroleum Research Fund [grant number 53482-DNI6]. R. DiStasio and B. Santra: Scientific Discovery through Advanced Computing (SciDAC) programme [grant numbers DE-SC0005180 and DE-SC0008626]. Resources used: National Energy Research Scientific Computing Center, supported by the Office of Science of the U.S. Department of Energy [contract number DE-AC02-05CH11231]; Argonne Leadership Computing Facility at Argonne National Laboratory, supported by the Office of Science of the U.S. Department of Energy [contract number DE-AC02-06CH11357].