Quantum cluster equilibrium model of N-methylformamide–water binary mixtures

Abstract

The established quantum cluster equilibrium (QCE) approach is refined and applied to Nmethylformamide (NMF) and its aqueous solution. The QCE method is split into two iterative cycles: one which converges to the liquid phase solution of the QCE equations and another which yields the gas phase. By comparing Gibbs energies, the thermodynamically stable phase at a given temperature and pressure is then chosen. The new methodology avoids metastable solutions and allows a different treatment of the mean-field interactions within the gas and liquid phases. These changes are of crucial importance for the treatment of binary mixtures. For the first time in a QCE study, the cis-trans-isomerism of a species (NMF) is explicitly considered. Cluster geometries and frequencies are calculated using density functional theory (DFT) and complementary coupled cluster single point energies are used to benchmark the DFT results. Independent of the selected quantum-chemical method, a large set of clusters is required for an accurate thermodynamic description of the binary mixture. The liquid phase of neat NMF is found to be dominated by the cyclic trans-NMF pentamer, which can be interpreted as a linear trimer that is stabilized by explicit solvation of two further NMF molecules. This cluster reflects the known hydrogen bond network preferences of neat NMF. C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

Activity coefficients of binary methanol alcohol mixtures from cluster weighting

“…As shown in earlier works, via the quantum cluster approach we are able to reproduce quantitatively the experimental Gibbs energies of mixing D mix G, using the density and phase transition temperature as only experimental input data. [24,25,59] The Gibbs energy of mixing at 328.15 K is depicted in Figure 6 for the binary mixtures of methanol with ethanol, n-propanol, isopropanol, n-butanol, iso-propanol, tert-butanol. Of all the investigated systems, methanol/ethanol is the one that most resembles an ideal mixture.…”

“…An alternative approach to face the challenge is based on the binary quantum cluster equilibrium (bQCE) theory. [23][24][25] bQCE is an extension of Weinhold's quantum cluster method for pure liquids [26][27][28][29][30] and has been successfully applied to predict the miscibility of binary mixtures, the ionic product of water, activity coefficients, and mole fraction dependent dissociation for weak acids. [25,[31][32][33][34] By applying models of statistical thermodynamics to quantum chemically calculated clusters, the thermodynamic description of neat liquids and their mixtures at non-zero temperature and pressure is possible in the condensed and gaseous phase.…”

Hydrogen Bonding and Vaporization Thermodynamics in Hexafluoroisopropanol‐Acetone and ‐Methanol Mixtures. A Joined Cluster Analysis and Molecular Dynamic Study

“…wherein b xv is the empirical exclusion volume parameter to correctly scale the cluster volume , which is sensitive to the choice of the volume method and the atomic radii used therein. In previous works, b xv was treated as temperature independent [27,32,33,35,38] . Here, we introduce a linear temperature dependence of b xv …”

“…Boltzmann and bQCE weighting were compared in the past by our group in the field of the computational calculation of vibrational circular dichroism spectra of bulk phase, showing the advantages of our method over Boltzmann weighting [29] . For this purpose we use our in‐house code Peacemaker 2.8, which has proven to be a valuable tool to investigate the thermodynamic properties of both neat and mixed systems [27,30–38] . The standard bQCE method involves optimization of two empirical parameters by fitting them to a set of experimental data such as boiling points or isobars; however, even for simple mixtures of organic solvents, these data are often unavailable in the literature.…”

Cluster-Based Thermodynamics of Interacting Dice in a Lattice

“…The binary quantum cluster equilibrium (bQCE) theory [ 18 , 19 , 20 , 21 , 22 , 23 ] uses clusters as a basis for estimating the activity coefficients of liquid mixtures, whereby the liquid phase is described by a so-called cluster gas, and the formation of the clusters from monomers is modeled like a chemical reaction.…”