Advanced dielectric continuum model of preferential solvation
Mikhail Basilevsky1, Alexey Odinokov, Ekaterina Nikitina
1Photochemistry Center, Russian Academy of Sciences, Moscow 119421, Russia.
The Journal of Chemical Physics
|January 22, 2009
Summary
A new continuum model describes solvation in binary solvent mixtures using density functional theory. It reveals how solvent composition and density affect ion solvation, particularly in benzene/dimethylsulfoxide (DMSO) mixtures.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Continuum models are essential for understanding solvation effects in chemical systems.
- Binary solvent mixtures present unique challenges due to coupled composition and density variations.
- Existing theories often simplify solvation shells, potentially missing crucial fine effects.
Purpose of the Study:
- To formulate a continuum model for solvation in binary solvent mixtures based on density functional theory.
- To investigate the spatial distribution of solvent composition and density around an ion.
- To analyze the composition dependence of solvation effects and compare with simulation data.
Main Methods:
- Formulation of a continuum model using density functional theory with composition (y) and density (z) variables.
- Derivation of local equilibrium conditions via free energy functional variation.
- Application to a Born-type ion in a benzene/dimethylsulfoxide (DMSO) mixture.
- Comparison with molecular dynamics (MD) simulations to obtain y(R) and z(R) profiles.
Main Results:
- Solvent density profiles z(R) showed minimal dependence on composition (y) for a given ion.
- A simplified model using z(R) from pure DMSO accurately predicted composition-dependent solvation effects.
- Local density augmentation (peak in z(R)) at the ion boundary explains fine solvation effects.
- Extremely dense solvation shells (z>>1) were observed for positive ions, challenging continuum model validity.
Conclusions:
- The developed continuum model effectively captures solvation in binary mixtures, especially for negative ions.
- The model highlights the importance of local density augmentation for accurate solvation predictions.
- Limitations of continuum models were identified for highly concentrated solvation shells around positive ions.
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