Ab initio molecular dynamics investigation of the concentration dependence of charged defect transport in basic solutions via calculation of the infrared spectrum

Zhongwei Zhu, Mark Tuckerman

Research output: Contribution to journalArticle

Abstract

The concentration dependence of the anomalous proton transport mechanism in aqueous KOD solution is studied using ab initio molecular dynamics. A high concentration of 13 M is chosen because of the availability of Raman and infrared spectroscopic data at this concentration. Differences in certain features of these spectra have been interpreted in terms of the so-called "proton hole" picture of the proton transport mechanism in basic solutions. The proton hole mechanism asserts that the charged defect transport in basic solutions follows the same mechanism as in acidic solutions (where the charged defect is H3O+) with all of the hydrogen-bond polarities reversed. By computing the infrared spectrum directly from an ab initio molecular dynamics simulation, we are able to validate our ab initio approach against the experimental data. However, the mechanism of charged defect transport that emerges from the simulation is considerably different from the proton hole mechanism and follows that recently reported by Tuckerman, et al. (Tuckerman, M.E.; Marx, D.; Parrinello, M. Nature 2002, 417, 925). For comparison, a lower concentration, 1.5 M, is also simulated and the transport mechanism compared to the high concentration case. It is found that the mechanisms are similar; however, the mobility of both K+ and OD- is slower at high concentration, a finding that is in keeping with the fact that the molar conductivity of electrolytes decreases with increasing concentration. Other similarities and differences between the two concentrations are highlighted, and a new interpretation of the spectral data is proposed.

Original languageEnglish (US)
Pages (from-to)8009-8018
Number of pages10
JournalJournal of Physical Chemistry B
Volume106
Issue number33
DOIs
StatePublished - Aug 22 2002

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Molecular dynamics
Protons
infrared spectra
molecular dynamics
Infrared radiation
Defects
defects
protons
Electrolytes
Hydrogen bonds
Availability
availability
Computer simulation
low concentrations
polarity
simulation
electrolytes
hydrogen bonds
aqueous solutions
conductivity

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Ab initio molecular dynamics investigation of the concentration dependence of charged defect transport in basic solutions via calculation of the infrared spectrum",
abstract = "The concentration dependence of the anomalous proton transport mechanism in aqueous KOD solution is studied using ab initio molecular dynamics. A high concentration of 13 M is chosen because of the availability of Raman and infrared spectroscopic data at this concentration. Differences in certain features of these spectra have been interpreted in terms of the so-called {"}proton hole{"} picture of the proton transport mechanism in basic solutions. The proton hole mechanism asserts that the charged defect transport in basic solutions follows the same mechanism as in acidic solutions (where the charged defect is H3O+) with all of the hydrogen-bond polarities reversed. By computing the infrared spectrum directly from an ab initio molecular dynamics simulation, we are able to validate our ab initio approach against the experimental data. However, the mechanism of charged defect transport that emerges from the simulation is considerably different from the proton hole mechanism and follows that recently reported by Tuckerman, et al. (Tuckerman, M.E.; Marx, D.; Parrinello, M. Nature 2002, 417, 925). For comparison, a lower concentration, 1.5 M, is also simulated and the transport mechanism compared to the high concentration case. It is found that the mechanisms are similar; however, the mobility of both K+ and OD- is slower at high concentration, a finding that is in keeping with the fact that the molar conductivity of electrolytes decreases with increasing concentration. Other similarities and differences between the two concentrations are highlighted, and a new interpretation of the spectral data is proposed.",
author = "Zhongwei Zhu and Mark Tuckerman",
year = "2002",
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AB - The concentration dependence of the anomalous proton transport mechanism in aqueous KOD solution is studied using ab initio molecular dynamics. A high concentration of 13 M is chosen because of the availability of Raman and infrared spectroscopic data at this concentration. Differences in certain features of these spectra have been interpreted in terms of the so-called "proton hole" picture of the proton transport mechanism in basic solutions. The proton hole mechanism asserts that the charged defect transport in basic solutions follows the same mechanism as in acidic solutions (where the charged defect is H3O+) with all of the hydrogen-bond polarities reversed. By computing the infrared spectrum directly from an ab initio molecular dynamics simulation, we are able to validate our ab initio approach against the experimental data. However, the mechanism of charged defect transport that emerges from the simulation is considerably different from the proton hole mechanism and follows that recently reported by Tuckerman, et al. (Tuckerman, M.E.; Marx, D.; Parrinello, M. Nature 2002, 417, 925). For comparison, a lower concentration, 1.5 M, is also simulated and the transport mechanism compared to the high concentration case. It is found that the mechanisms are similar; however, the mobility of both K+ and OD- is slower at high concentration, a finding that is in keeping with the fact that the molar conductivity of electrolytes decreases with increasing concentration. Other similarities and differences between the two concentrations are highlighted, and a new interpretation of the spectral data is proposed.

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