Abstract
With a longer-term goal of addressing the comparative behavior of the aqueous halides F-, Cl-, Br-, and I-on the basis of quasi-chemical theory (QCT), here we study structures and free energies of hydration clusters for those anions. We confirm that energetically optimal (H2O)nX clusters, with X = Cl-, Br-, and I-, exhibit surface hydration structures. Computed free energies, based on optimized surface hydration structures utilizing a harmonic approximation, typically (but not always) disagree with experimental free energies. To remedy the harmonic approximation, we utilize single-point electronic structure calculations on cluster geometries sampled from an AIMD (ab initio molecular dynamics) simulation stream. This rough-landscape procedure is broadly satisfactory and suggests unfavorable ligand crowding as the physical effect addressed. Nevertheless, this procedure can break down when n≳4, with the characteristic discrepancy resulting from a relaxed definition of clustering in the identification of (H2O)nX clusters, including ramified structures natural in physical cluster theories. With ramified structures, the central equation for the present rough-landscape approach can acquire some inconsistency. Extension of these physical cluster theories in the direction of QCT should remedy that issue, and should be the next step in this research direction.
| Original language | English |
|---|---|
| Article number | 3087 |
| Journal | Molecules |
| Volume | 26 |
| Issue number | 11 |
| DOIs | |
| State | Published - Jun 1 2021 |
Funding
Acknowledgments: This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. This work was carried out in part at Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy under contract DE-AC05-00OR22725. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government. The work of DTG and LRP was supported in part by by the Laboratory Directed Research and Development (LDRD) Program at Los Alamos National Laboratory under project number 20190057DR. DMR was supported by Oak Ridge National Laboratory under contract DE-AC05-00OR22725. The work of SBR was support in part by the LDRD Program at Sandia National Laboratories. This research also used resources provided by the Los Alamos National Laboratory Institutional Computing Program, supported by the U. S. Department of Energy National Nuclear Security Administration under Contract No. 89233218CNA000001. We thank Robert P. Currier and Katie A. Maerzke for their assistance.
Keywords
- Halides
- Hofmeister series
- Ion hydration
- Physical cluster theory
- Specific ion effects