Anomalous thermodynamic properties of water: What is wrong and/or missing in SAFT equations? Ivo Nezbeda Journal of Chemical Physics, 2026 This work is motivated by a simple question: why have none of the Statistical Association Fluid Theory (SAFT)-type equations of state proposed for water so far—perturbation-like models with several adjustable parameters—been able to reproduce water’s thermodynamic properties over a broad range of conditions, even at a qualitative level? We examine two theoretical, analytically treatable water models of different character, i.e., models that provide genuine predictions without being parameterized to experimental thermodynamic data. The first is an extremely simple toy model designed to capture the essential physics of association. The second is a short-range model derived from the realistic TIP4P force field and intended for the same purpose. For both models, we compute the isobaric temperature dependence of the density and three response functions: the isothermal compressibility, the isobaric expansivity, and the isobaric heat capacity over a wide range of thermodynamic conditions. The results are compared with experimental data and with predictions from the best-performing SAFT equation identified in our earlier work. We show that the short-range models correctly capture the characteristic behavior of the density and the isothermal compressibility, as well as the critical compressibility factor and the universal expansivity point (the crossing point) of the isobaric expansivity—features that are generally missing in SAFT-type equations. However, these short-range models fail to reproduce the heat capacity, which is an expected consequence of missing long-range electrostatic contributions. We argue that the shortcomings of existing SAFT equations for water stem from (i) the arbitrariness in defining the reference system, (ii) neglecting the van der Waals interaction in the reference completely, (iii) the ambiguity of the correction terms, and (iv) the subsequent parameter-estimation strategy.
Toward an accurate equation of state for hard polyhedron fluids J. Škvára, I. Nezbeda Journal of Chemical Physics, 2025 An alternative to corrected high-order virial expansions to derive an accurate equation of state for fluids made up of bodies of extreme nonsphericity is proposed. Instead of empirically corrected virial expansions of high order, we use the virial coefficients within the functional form of the hard convex body equation of state. The balance between the accuracy of the equation and the number of the used virial coefficients and adjustable parameters is examined. First, for the fluid of tetrahedra, the recommended equation with only three virial coefficients and four adjustable parameters is considered for the complete set of fourteen polyhedron fluids. An excellent agreement with simulation data is achieved for all the models. The next equation in accuracy is the equation of Tian et al. [Phys. Chem. Chem. Phys. 21, 13109 (2019)], which employs seven virial coefficients and two adjustable parameters. The results are also compared with purely theoretical equations, which are considerably inferior and have unpredictable accuracy for different models.
Structure of liquids from reference hard body fluids: Additive vs non-additive hard body models J. Škvára, I. Nezbeda Journal of Chemical Physics, 2025 Following the early simulation results for simple liquids, various hard body fluids have been used in molecular-based equations of state as a leading/reference term. This has been justified for normal liquids by the similarity of their structure, but for polar and associating ones, a direct application of hard body models has not been considered so far. Viewing the hard body models, fused-hard-sphere bodies, as simple geometrical objects, their mutual interaction is additive. However, when accounting for the mutual effect of the site–site interactions, the individual hard sphere–hard sphere interactions may become non-additive, and consequently, the resulting interaction between the hard bodies becomes non-additive, which may also affect their structure. The effect of the non-additivity on the structural properties, the site–site and dipole–dipole correlation functions are analyzed in detail by considering three polar fluids, quadrupolar carbon dioxide, dipolar acetonitrile, and acetone, as well as two associating fluids, methanol and water. The modification of the mutual geometry in the non-additive models leads to differences both in their structural and orientation correlations. The comparison of the structure of the non-additive purely repulsive hard-body models with those of the empirical models of the chosen real liquids shows surprising similarities, which extends the possibilities of the direct application of the hard-body fluids as reference systems in perturbation theories.
Anomalous thermodynamic properties of water: What is wrong and/or missing in SAFT equations? I Nezbeda The Journal of Chemical Physics 164 (19) , 2026 2026
Excluded volume and molecular field in the Lennard-Jones fluid: a modified first-order perturbation theory A Trokhymchuk, V Hordiichuk, R Melnyk, I Nezbeda arXiv preprint arXiv:2604.25882 , 2026 2026
Toward an accurate equation of state for hard polyhedron fluids J Škvára, I Nezbeda The Journal of Chemical Physics 163 (1) , 2025 2025
Structure of liquids from reference hard body fluids: Additive vs non-additive hard body models J Škvára, I Nezbeda The Journal of Chemical Physics 162 (16) , 2025 2025 Citations: 1
A remark on hard body fluids: density versus packing fraction and excluded volume I Nezbeda, J Škvára Molecular Physics 122 (21-22), e2304648 , 2024 2024 Citations: 3
Corrigendum to “Structure and thermodynamics of a short-range Lennard-Jones fluid reference”[J. Mol. Liquids 386 (2023) 122483] V Hordiichuk, J Škvára, A Trokhymchuk, I Nezbeda Journal of Molecular Liquids 390, 123087 , 2023 2023
Corrigendum to “Supercooled water in two dimensions: Structure and thermodynamics of the Mercedes-Benz model”[J. Mol. Liquids 386 (2023) 122445] J Škvára, I Nezbeda, T Urbic Journal of Molecular Liquids 390, 122953 , 2023 2023
Structure and thermodynamics of a short-range Lennard-Jones fluid reference V Hordiichuk, J Škvára, A Trokhymchuk, I Nezbeda Journal of Molecular Liquids 386, 122483 , 2023 2023 Citations: 3
Supercooled water in two dimensions: Structure and thermodynamics of the Mercedes-Benz model J Škvára, I Nezbeda, T Urbic Journal of molecular liquids 386, 122445 , 2023 2023
Assessing the quality of SAFT equations for the vapor-liquid equilibrium of pure water M Klajmon, I Nezbeda Journal of Molecular Liquids 376, 121414 , 2023 2023 Citations: 4
Thermodynamics and structure of supercooled water. II. J Škvára, I Nezbeda Journal of Molecular Liquids 367, 120508 , 2022 2022 Citations: 2
On a molecular origin of properties of water I Nezbeda Journal of Molecular Liquids 365, 120100 , 2022 2022 Citations: 2
Thermodynamic properties of water from SAFT and CPA equations of state: A comprehensive assessment I Nezbeda, M Klajmon, J Hrubý Journal of Molecular Liquids 362, 119769 , 2022 2022 Citations: 24
On a flaw in the development of simple (primitive)-model-based equations of state for water I Nezbeda Chemical Physics Letters 790, 139332 , 2022 2022 Citations: 3
Structure of Simple Dipolar Water-Like Fluids: Primitive Model and Hard Tetrahedra I Nezbeda Frontiers in Chemistry 9, 783741 , 2021 2021 Citations: 2
Thermodynamic perturbation theory and equation of state developments I Nezbeda arXiv preprint arXiv:2110.04496 , 2021 2021
On industrial applications of molecular simulations I Nezbeda, J Škvára Molecular Simulation 47 (10-11), 846-856 , 2021 2021 Citations: 5
Yuriy Kalyuzhnyi’s lifetime in Science I Nezbeda, V Vlachy, A Trokhymchuk Condensed Matter Physics 24 (3), 1-3 , 2021 2021
Integral equation theory for mixtures of spherical and patchy colloids. 2. Numerical results YV Kalyuzhnyi, I Nezbeda, PT Cummings Soft Matter 17 (12), 3513-3519 , 2021 2021 Citations: 6
On molecular-based equations of state: Perturbation theories, simple models, and SAFT modeling I Nezbeda Frontiers in Physics 8, 287 , 2020 2020 Citations: 26
MOST CITED SCHOLAR PUBLICATIONS
P-V-T behaviour of hard body fluids. Theory and experiment T Boublík, I Nezbeda Collection of Czechoslovak chemical communications 51 (11), 2301-2432 , 1986 1986 Citations: 415
The Lennard-Jones fluid: an accurate analytic and theoretically-based equation of state J Kolafa, I Nezbeda Fluid Phase Equilibria 100, 1-34 , 1994 1994 Citations: 401
Vapor-liquid equilibria from the triple point up to the critical point for the new generation of TIP4P-like models: TIP4P/Ew, TIP4P/2005, and TIP4P/ice C Vega, JLF Abascal, I Nezbeda The Journal of chemical physics 125 (3) , 2006 2006 Citations: 345
Monte Carlo simulations on primitive models of water and methanol J Kolafa, I Nezbeda Molecular Physics 61 (1), 161-175 , 1987 1987 Citations: 206
Equation of state for hard dumbbells T Boublik, I Nezbeda Chemical Physics Letters 46 (2), 315-316 , 1977 1977 Citations: 182
Primitive model of water: II. Theoretical results for the structure and thermodynamic properties I Nezbeda, J Kolafa, YV Kalyuzhnyi Molecular physics 68 (1), 143-160 , 1989 1989 Citations: 178
A new version of the insertion particle method for determining the chemical potential by Monte Carlo simulation I Nezbeda, J Kolafa Molecular Simulation 5 (6), 391-403 , 1991 1991 Citations: 155
Statistical thermodynamics of simple liquids and their mixtures T Boublík, I Nezbeda, K Hlavatý (No Title) , 1980 1980 Citations: 152
Recent progress in molecular simulation of aqueous electrolytes: Force fields, chemical potentials and solubility I Nezbeda, F Moučka, WR Smith Molecular Physics 114 (11), 1665-1690 , 2016 2016 Citations: 145
A simple model for associated fluids WR Smith, I Nezbeda The Journal of chemical physics 81 (8), 3694-3699 , 1984 1984 Citations: 137
An examination of the five-site potential (TIP5P) for water M Lısal, J Kolafa, I Nezbeda The Journal of chemical physics 117 (19), 8892-8897 , 2002 2002 Citations: 127
Molecular simulation of aqueous electrolyte solubility. 2. Osmotic ensemble Monte Carlo methodology for free energy and solubility calculations and application to NaCl F Moucka, M Lísal, J Skvor, J Jirsák, I Nezbeda, WR Smith The Journal of Physical Chemistry B 115 (24), 7849-7861 , 2011 2011 Citations: 118
Hard-sphere radial distribution function again A Trokhymchuk, I Nezbeda, J Jirsák, D Henderson The Journal of chemical physics 123 (2) , 2005 2005 Citations: 112
Molecular force fields for aqueous electrolytes: SPC/E-compatible charged LJ sphere models and their limitations F Moučka, I Nezbeda, WR Smith The Journal of chemical physics 138 (15) , 2013 2013 Citations: 106
Accurate vapour–liquid equilibrium calculations for complex systems using the reaction Gibbs ensemble Monte Carlo simulation method M Lísal, WR Smith, I Nezbeda Fluid Phase Equilibria 181 (1-2), 127-146 , 2001 2001 Citations: 103
Virial expansion and an improved equation of state for the hard convex molecule system I Nezbeda Chemical Physics Letters 41 (1), 55-58 , 1976 1976 Citations: 101
Simple short-ranged models of water and their application. A review I Nezbeda Journal of molecular liquids 73, 317-336 , 1997 1997 Citations: 98
Detection and Characterization of Structural Changes in the Hard-Disk Fluid<? format?> under Freezing and Melting Conditions F Moučka, I Nezbeda Physical review letters 94 (4), 040601 , 2005 2005 Citations: 94
Chemical potentials, activity coefficients, and solubility in aqueous NaCl solutions: Prediction by polarizable force fields F Moucka, I Nezbeda, WR Smith Journal of Chemical Theory and Computation 11 (4), 1756-1764 , 2015 2015 Citations: 84
A family of primitive models of water: three-, four and five-site models I Nezbeda, J Slovak Molecular Physics 90 (3), 353-372 , 1997 1997 Citations: 84
