Intermolecular Interactions in Complex Liquids: Effective Fragment Potential Investigation of Water–tert-Butanol Mixtures

Abstract

Structure and bonding patterns in tert-butanol (TBA)-water mixtures are investigated by using molecular dynamics simulations with the effective fragment potential (EFP) method. EFP is a model potential in which all parameters are obtained from a set of ab initio calculations on isolated fragment molecules. Mixed-basis EFP potentials (called "EFPm") for water and TBA molecules were prepared and tested in this work. The accuracy of these EFP potentials is justified by comparison of structures and binding energies in water, TBA, and water-TBA dimers with MP2/6-311++G(d,p) data. It has been found that the discrepancies between EFP and MP2 do not exceed 0.1 Å in intermolecular distances and 1 kcal/mol in binding energies. Structures of TBA-water solutions with 0.0, 0.06, 0.11, 0.16, and 0.50 TBA mole fractions were analyzed by using radial distribution functions (RDFs) and coordination numbers. These results suggest that, at low TBA concentrations, the structure of water is enhanced and water and TBA are not homogeneously mixed at the molecular level. In the equimolar TBA-water solution, the microscopic mixing is more complete. Analysis of the energy components in TBA-water solutions shows that, while the electrostatic and exchange-repulsion terms provide the largest contributions to the total potential energy, the relative importance of the polarization and dispersion terms depends on the concentration of TBA. With an increase of TBA concentration, the fraction of the dispersion energy increases, while the fraction of polarization energy diminishes. However, both polarization and dispersion terms are essential for accurate description of these systems.

Fluctuating micro-heterogeneity in water–tert-butyl alcohol mixtures and lambda-type divergence of the mean cluster size with phase transition-like multiple anomalies

“…Indeed, several simulation studies [42][43][44][45][46][47][48][49][50] have been performed on this important binary mixture, at different concentrations and using different force fields. Early in the 1990's, Tanaka and Nakanishi [42] performed simulations on this system and noted self-aggregation of TBA molecules at mole fraction 0.17.…”

CHAPTER 7. Excess Volumes of Liquid Nonelectrolyte Mixtures

“…416,417 This concept of micro-heterogeneity is supported by computer simulations. 379, [418][419][420][421][422] We note that the polar interaction of water with the OH-group of an alcohol may contribute more to the thermodynamic properties of aqueous mixtures of alcohols than hydrophobic effects, a point-of-view which has recently been advanced by Ben-Naim. [423][424][425] Volumetric properties of aqueous solutions of tert-butanol have been determined by many researchers, for instance, in chronological sequence, by Nakanishi, 408 Franks and Smith, 426 de Visser et al, 407 Hvidt et al, 427 Sakurai, 428 Kubota et al, 370 Kim and Marsh, 429 Kipkemboi and Easteal,430 and most recently, by Egorov and Makarov.…”

Effective fragment potential method in Q‐CHEM: A guide for users and developers

“…[16][17][18][19][20][21][22][23][24][25][26] Recently, a systematic benchmark study of EFP using a popular S22 dataset for noncovalent interactions has been published. [16][17][18][19][20][21][22][23][24][25][26] Recently, a systematic benchmark study of EFP using a popular S22 dataset for noncovalent interactions has been published.…”

“…The performance of EFP for noncovalent interactions has been benchmarked against high-level ab initio methods for a variety of systems, including those dominated by hydrogen bonding, p À p, or mixed interactions. [16][17][18][19][20][21][22][23][24][25][26] Recently, a systematic benchmark study of EFP using a popular S22 dataset for noncovalent interactions has been published. [27] The reported [27] mean absolute deviation (MAD) of EFP relative to the high-level ab initio results, CCSD(T) (coupled-cluster with single and double substitutions and perturbative inclusion of triple excitations) extrapolated to the complete basis set limit, was 0.9 kcal/mol, which is comparable to the accuracy of MP2 and outperforms classical force fields.…”