On the Kirkwood–Buff inversion procedure

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Kirkwood-Buff or Fluctuation Solution Theory can be used to provide experimental pair fluctuations, and/or integrals over the pair distribution functions, from experimental thermodynamic data on liquid mixtures. Here, this type of approach is used to provide triplet and quadruplet fluctuations, and the corresponding integrals over the triplet and quadruplet distribution functions, in a purely thermodynamic manner that avoids the use of structure factors. The approach is then applied to binary mixtures of water + methanol and benzene + methanol over the full composition range under ambient conditions. The observed correlations between the different species vary significantly with composition. The magnitude of the fluctuations and integrals appears to increase as the number of the most polar molecule involved in the fluctuation or integral also increases. A simple physical picture of the fluctuations is provided to help rationalize some of these variations. C 2015 AIP Publishing LLC. [http://dx

Section: B Symmetric Ideal Solutionsmentioning

confidence: 99%

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for liquid mixtures

Ploetz

Smith

2015

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“…Given the experimental measurements of the partial molar volumes, the isothermal compressibility of the solution, and density, KB theory described above can be reversed by an inversion procedure to obtain KBIs, 48,49 which can be directly compared to those computed based on RDFs obtained from integral equations models of solution or molecular dynamics simulations, as in the present study,…”

Section: Theorymentioning

confidence: 99%

“…5 along with experimental KBIs of aqueous NMA solutions computed from experimental data 61,62 from inverse KB procedure. 48,49 Simulated KBIs were computed via Eq. (1) by integrating the RDFs via the trapezoidal rule and taking the average between 10 and 15 Å.…”

Section: Kirkwood-buff Solution Analysismentioning

confidence: 99%

Kirkwood-Buff analysis of aqueous N-methylacetamide and acetamide solutions modeled by the CHARMM additive and Drude polarizable force fields

Lin

Lopes

Roux

et al. 2013

Kirkwood-Buff analysis was performed on aqueous solutions of N-methylacetamide and acetamide using the Chemistry at HARvard Molecular Mechanics additive and Drude polarizable all-atom force fields. Comparison of a range of properties with experimental results, including Kirkwood-Buff integrals, excess coordination numbers, solution densities, partial molar values, molar enthalpy of mixing, showed both models to be well behaved at higher solute concentrations with the Drude model showing systematic improvement at lower solution concentrations. However, both models showed difficulties reproducing experimental activity derivatives and the excess Gibbs energy, with the Drude model performing slightly better. At the molecular level, the improved agreement of the Drude model at low solute concentrations is due to increased structure in the solute-solute and solute-solvent interactions. The present results indicate that the explicit inclusion of electronic polarization leads to improved modeling of dilute solutions even when those properties are not included as target data during force field optimization.

“…This can be shown to be true for n =1-4 components. 21 Here we provide rigorous proof that this expression is valid for any number of components at constant T and P. Furthermore, we also determine the corresponding expressions for the KBIs which result in ideal behavior on the molality and molarity concentration scales. The results are then illustrated using data obtained from computer simulations.…”

Section: G Ijmentioning

confidence: 99%

“…The KBIs for these solutions can be expressed in terms of the isothermal compressibility ͑ T ͒ and molar volumes ͑V i ͒ of the pure components at the same T and P. Expressions for binary, ternary, and quaternary solutions are available. 2,20,21 Ben-Naim has also shown that SI solutions including up to four components satisfy ⌬G ij = G ii + G jj −2G ij = 0 for all i , j pairs. 22 Our recent analysis of the results obtained from the KB theory of solutions for n =1 to 4 components proposed the following general expression for the KBIs: 21 …”

Section: Introductionmentioning

confidence: 99%

Kirkwood–Buff integrals for ideal solutions

Ploetz

Bentenitis²,

Smith³

2010

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The Kirkwood-Buff ͑KB͒ theory of solutions is a rigorous theory of solution mixtures which relates the molecular distributions between the solution components to the thermodynamic properties of the mixture. Ideal solutions represent a useful reference for understanding the properties of real solutions. Here, we derive expressions for the KB integrals, the central components of KB theory, in ideal solutions of any number of components corresponding to the three main concentration scales. The results are illustrated by use of molecular dynamics simulations for two binary solutions mixtures, benzene with toluene, and methanethiol with dimethylsulfide, which closely approach ideal behavior, and a binary mixture of benzene and methanol which is nonideal. Simulations of a quaternary mixture containing benzene, toluene, methanethiol, and dimethylsulfide suggest this system displays ideal behavior and that ideal behavior is not limited to mixtures containing a small number of components.