Molecular dynamics investigation of alkali metal ions in liquid and aqueous ammonia

Esam A. Orabi, Guillaume Lamoureux

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

A polarizable potential model for M+-NH3 interactions (M+ = Li+, Na+, K+, Rb+, Cs+) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M+(NH3) n (n = 2-4) and M+(NH3)n(H 2O)m (n, m = 1-3 and n + m ≤ 4) clusters and gives relative solvation free energies in liquid ammonia in good agreement with experimental data, without further adjustments. It also reproduces binding cooperativity in ion-ammonia and ion-ammonia-water clusters. The model is used in molecular dynamics simulations of isolated ions in liquid ammonia and in aqueous ammonia solutions with various ammonia molar fractions (0.0 ≤ x NH3 ≤ 1.0). Simulations in liquid ammonia show coordination numbers of 4.0 for Li+, 5.3 for Na+, 6.1 for K +, 6.7 for Rb+, and 7.7 for Cs+, in very good agreement with available experimental results. Simulations of ions in aqueous ammonia show preferential solvation by water in their first solvation shells and preferential solvation by ammonia in their second shells. Potentials of mean force are calculated between each ion and NH3 in liquid water, and between each ion and H2O in liquid ammonia. The results suggest that, in liquid water, Li+ and Na+ bind NH3 in their second solvation shells only, while Cs+ binds NH3 in its first solvation shell only (K+ and Rb+ ions show only weak affinity for NH3 in water). In liquid ammonia, the ions bind H 2O in their first solvation shells with an affinity following the trend Li+ > Na+ > K+ ≈ Rb+ > Cs+.

Original languageEnglish (US)
Pages (from-to)2324-2338
Number of pages15
JournalJournal of Chemical Theory and Computation
Volume9
Issue number5
DOIs
StatePublished - May 14 2013
Externally publishedYes

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Alkali Metals
liquid ammonia
Alkali metals
Ammonia
alkali metals
Metal ions
Molecular dynamics
ammonia
metal ions
molecular dynamics
solvation
Solvation
Liquids
Ions
ions
water
Water
affinity
simulation
liquids

All Science Journal Classification (ASJC) codes

  • Computer Science Applications
  • Physical and Theoretical Chemistry

Cite this

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title = "Molecular dynamics investigation of alkali metal ions in liquid and aqueous ammonia",
abstract = "A polarizable potential model for M+-NH3 interactions (M+ = Li+, Na+, K+, Rb+, Cs+) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M+(NH3) n (n = 2-4) and M+(NH3)n(H 2O)m (n, m = 1-3 and n + m ≤ 4) clusters and gives relative solvation free energies in liquid ammonia in good agreement with experimental data, without further adjustments. It also reproduces binding cooperativity in ion-ammonia and ion-ammonia-water clusters. The model is used in molecular dynamics simulations of isolated ions in liquid ammonia and in aqueous ammonia solutions with various ammonia molar fractions (0.0 ≤ x NH3 ≤ 1.0). Simulations in liquid ammonia show coordination numbers of 4.0 for Li+, 5.3 for Na+, 6.1 for K +, 6.7 for Rb+, and 7.7 for Cs+, in very good agreement with available experimental results. Simulations of ions in aqueous ammonia show preferential solvation by water in their first solvation shells and preferential solvation by ammonia in their second shells. Potentials of mean force are calculated between each ion and NH3 in liquid water, and between each ion and H2O in liquid ammonia. The results suggest that, in liquid water, Li+ and Na+ bind NH3 in their second solvation shells only, while Cs+ binds NH3 in its first solvation shell only (K+ and Rb+ ions show only weak affinity for NH3 in water). In liquid ammonia, the ions bind H 2O in their first solvation shells with an affinity following the trend Li+ > Na+ > K+ ≈ Rb+ > Cs+.",
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Molecular dynamics investigation of alkali metal ions in liquid and aqueous ammonia. / Orabi, Esam A.; Lamoureux, Guillaume.

In: Journal of Chemical Theory and Computation, Vol. 9, No. 5, 14.05.2013, p. 2324-2338.

Research output: Contribution to journalArticle

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T1 - Molecular dynamics investigation of alkali metal ions in liquid and aqueous ammonia

AU - Orabi, Esam A.

AU - Lamoureux, Guillaume

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AB - A polarizable potential model for M+-NH3 interactions (M+ = Li+, Na+, K+, Rb+, Cs+) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M+(NH3) n (n = 2-4) and M+(NH3)n(H 2O)m (n, m = 1-3 and n + m ≤ 4) clusters and gives relative solvation free energies in liquid ammonia in good agreement with experimental data, without further adjustments. It also reproduces binding cooperativity in ion-ammonia and ion-ammonia-water clusters. The model is used in molecular dynamics simulations of isolated ions in liquid ammonia and in aqueous ammonia solutions with various ammonia molar fractions (0.0 ≤ x NH3 ≤ 1.0). Simulations in liquid ammonia show coordination numbers of 4.0 for Li+, 5.3 for Na+, 6.1 for K +, 6.7 for Rb+, and 7.7 for Cs+, in very good agreement with available experimental results. Simulations of ions in aqueous ammonia show preferential solvation by water in their first solvation shells and preferential solvation by ammonia in their second shells. Potentials of mean force are calculated between each ion and NH3 in liquid water, and between each ion and H2O in liquid ammonia. The results suggest that, in liquid water, Li+ and Na+ bind NH3 in their second solvation shells only, while Cs+ binds NH3 in its first solvation shell only (K+ and Rb+ ions show only weak affinity for NH3 in water). In liquid ammonia, the ions bind H 2O in their first solvation shells with an affinity following the trend Li+ > Na+ > K+ ≈ Rb+ > Cs+.

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