The primary goal of the eighth industrial fluid properties simulation challenge was to test the ability of molecular simulation methods to predict the adsorption of organic adsorbates in activated carbon materials. The challenge focused on the adsorption of perfluorohexane in the activated carbon standard BAM-P109. Entrants were challenged to predict the adsorption of perfluorohexane in the activated carbon at a temperature of 273K and at relative pressures of 0.1, 0.3, and 0.6. The relative pressure (P/P-o) is defined as that relative to the bulk saturation pressure predicted by the fluid model at a given temperature (273K in this case). The predictions were judged by comparison to a set of experimentally determined values, which are published here for the first time and were not disclosed to the entrants prior to the challenge. Benchmark experimental studies, described herein, were also carried out and provided to entrants in order to aid in the development of new force fields and simulation methods to be employed in the challenge. These studies included argon, carbon dioxide, and water adsorption in the BAM-P109 activated carbon as well as X-ray diffraction, X-ray microtomography, photoelectron spectroscopy, and atomic emission spectroscopy studies of BAM-P109. Several concurrent studies were carried out for the BAM-P108 activated carbon. These are included in the current manuscript for comparison.

The primary goal of the seventh industrial fluid properties simulation challenge was to test the ability of molecular simulation methods to predict the adsorption of organic adsorbates in zeolitic materials. The challenge focused, in particular, on the adsorption of perfluorohexane in the BCR-704 Faujasite zeolite. Entrants were challenged to predict the adsorption of perfluorohexane in the zeolite at 293 K and at relative pressures of 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, and 0.8. The relative pressure (P/P-o) is defined as that relative to the bulk saturation pressure predicted by the model at a given temperature (293 K in this case). The predictions were judged by comparison to a set of experimentally determined values which are published here for the first time and were not disclosed prior to the challenge to the entrants.Additional benchmark experimental studies, also described here-in, were carried out and provided to entrants in order to aid in the development of new force fields and simulation methods to be employed in the challenge. These studies included argon and nitrogen adsorption in the BCR-704 Faujasite zeolite. Elemental analysis of the BCR-704 Faujasite type zeolite was also available to entrants via the Institute of Reference Materials and Measurement (IRMM) report EUR 21065 [1]. (C) 2014 Elsevier B.V. All rights reserved.

Simulations and experiments were carried out to explore the solvent extraction of ethanol from aqueous solution using a series of seven 10‐carbon alcohols. It is shown that configurational‐bias Monte Carlo simulations in the Gibbs ensemble coupled with the TraPPE‐UA force field can be utilized for predictive screening of the different extraction abilities (in terms of capacity factor and selectivity) of these alcohols. Analysis of the simulation trajectories indicates that extraction capacity is connected to the stabilization of larger ethanol/water cluster in the organic solvent, whereas selectivity is improved when smaller ethanol/water clusters are more prevalent. © 2013 American Institute of Chemical Engineers AIChE J , 59: 3065–3070, 2013

Hildebrand solubility parameters are predicted from molecular simulations using the transferable potentials for phase equilibrium-united atom (TraPPE-UA) and Dreiding force fields for the n-alkyl acrylate and methacrylate esters (n <= 10), as well as the 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, isooctyl esters of acrylic acid, and the 2-hydroxyethyl ester of methacrylic acid. The TraPPE-UA force field yields very accurate solubility parameters (with a mean unsigned percent error of 2%, or 0.2 Hildebrand units), whereas the Dreiding force field overpredicts the solubility parameter in every case examined. Correlations based on the normal boiling point or the refractive index do not yield satisfactory results for this monomer set with the former overestimat-ing the magnitude and the latter yielding the incorrect sign for the decrease in the solubility parameter with chain length. Simulations With the TraPPE-UA force field yield solubility parameters for binary mixtures of methyl methacrylate with 2-ethylhexyl or isooctyl acrylate, which are very well described by a linear interpolation using the pure compound cohesive energies and molar volumes, whereas those for mixtures with 2-hydroxyethyl acrylate or methacrylate small positive deviations due to structural microheterogeneity. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1-9, 2010

Computational results are reported for the ground and low-lying excited electronic states of Al(3)(-) and Al(3) and compared with the available spectroscopic data. In agreement with previous assignments, the six photodetachment transitions observed in the vibrationally resolved 488 nm photoelectron spectrum of Al(3)(-) are assigned as arising from the ground X (1)A(1) (')((1)A(1)) and excited (3)B(2) states of Al(3)(-) and accessing the ground X (2)A(1)(')((2)A(1)) and excited (2)A(2)(")((2)B(1)), (4)A(2), and (2)B(2) states of Al(3) (with C(2v) labels for D(3h) states in parentheses). Geometries and vibrational frequencies obtained by PBE0 hybrid density functional calculations using the 6-311+G(3d2f) basis set and energies calculated using coupled cluster theory with single and double excitations and a quasiperturbative treatment of connected triple excitations (CCSD(T)) with the aug-cc-pVxZ {x=D, T, Q} basis sets with exponential extrapolation to the complete basis set limit are in good agreement with experiment. Franck-Condon spectra calculated in the harmonic approximation, using either the Sharp-Rosenstock-Chen method which includes Duschinsky rotation or the parallel-mode Hutchisson method, also agree well with the observed spectra. Possible assignments for the higher-energy bands observed in the previously reported UV photoelectron spectra are suggested. Descriptions of the photodetachment transition between the Al(3)(-) and Al(3) ground states in terms of natural bond order (NBO) analyses and total electron density difference distributions are discussed. A reinterpretation of the vibrational structure in the resonant two-photon ionization spectrum of Al(3) is proposed, which supports its original assignment as arising from the X (2)A(1)(') ground state, giving an Al(3) bond dissociation energy, D(0)(Al(2)-Al), of 2.403+/-0.001 eV. With this reduction by 0.3 eV from the currently recommended value, the present calculated dissociation energies of Al(3), Al(3)(-), and Al(3)(+) are consistent with the experimental data.

An extension of the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field to acrylate and methacrylate monomers is presented. New parameters were fit to the liquid density, normal boiling point, saturated vapor pressure, and (where experimentally available) critical constants of 1,3-butadiene, isoprene, methyl acrylate, and methyl methacrylate using Gibbs ensemble Monte Carlo simulations. Excellent agreement with experiment was obtained for the parametrization compounds and seven additional acrylate and methacrylate compounds, with average errors in liquid density and normal boiling point of approximately 1%. The TraPPE-UA force field also predicts accurate heats of vaporization at 298 K. In addition, Gibbs ensemble Monte Carlo simulations of binary vapor-liquid equilibria for the mixtures methyl acrylate/1-butanol and methyl acrylate/n-decane show that the TraPPE-UA acrylate force field performs well in mixtures with both polar and nonpolar molecules. These simulations also indicate structural microheterogeneity in the liquid phase of these mixtures.

The extension of molecular mechanics to reactive systems, metals, and covalently bonded clusters with variable coordination numbers requires new functional forms beyond those popular for organic chemistry and biomolecules. Here we present a new scheme for reactive molecular mechanics, which is denoted as the valence-bond order model, for approximating reactive potential energy surfaces in large molecules, clusters, nanoparticles, solids, and other condensed-phase materials, especially those containing metals. The model is motivated by a moment approximation to tight binding molecular orbital theory, and we test how well one can approximate potential energy surfaces with a very simple functional form involving only interatomic distances with no explicit dependence on bond angles or dihedral angles. For large systems the computational requirements scale linearly with system size, and no diagonalizations or iterations are required; thus the method is well suited to large-scale simulations. The method is illustrated here by developing a force field for particles and solids composed of aluminum and hydrogen. The parameters were optimized against both interaction energies and relative interaction energies. The method performs well for pure aluminum clusters, nanoparticles, and bulk lattices and reasonably well for pure hydrogen clusters; the mean unsigned error per atom for the aluminum-hydrogen clusters is 0.1 eV/atom.

Holthausen has recently provided a comprehensive study of density functional theory for calculating the s/d excitation energies of the 3d transition metal cations. This study did not include the effects of scalar relativistic effects, and we show here that the inclusion of scalar relativistic effects significantly alters the conclusions of the study. We find, contrary to the previous study, that local functionals are more accurate for the excitation energies of 3d transition method cations than hybrid functionals. The most accurate functionals, of the 38 tested, are SLYP, PBE, BP86, PBELYP, and PW91.

Several semiempirical tight-binding models are parametrized and tested for aluminum clusters and nanoparticles using a data set of 808 accurate AlN (N = 2-177) energies and geometries. The effects of including overlap when solving the secular equation and of incorporating many-body (i.e., nonpairwise) terms in the repulsion and electronic matrix elements are studied. Pairwise orthogonal tight-binding (TB) models are found to be more accurate and their parametrizations more transferable (for particles of different sizes) than both pairwise and many-body nonorthogonal tight-binding models. Many-body terms do not significantly improve the accuracy or transferability of orthogonal TB, whereas some improvement in the nonorthogonal models is observed when many-body terms are included in the electronic Hamiltonian matrix elements.

Efficient simulation methods are presented for determining the standard Gibbs free energy changes for the reactions, M + Mn-1 <-> M-n (R1), involved in the formation of atomic clusters and nanoparticles (also called particles) in the vapor phase. The standard Gibbs free energy of formation (Delta(f)G degrees) of a particle is obtained from these Gibbs free energy changes (Delta G degrees) by a recursion relationship using the experimental Delta(f)G degrees of the monomer. In the present study, this method has been applied to reactions involving Al-n particles with n = 2-60. This method has been validated for n = 2, where the experimental thermodynamic properties of Al-2 have been recompiled using the latest available experimental or highly accurate theoretical data. For n = 2-4, two completely different approaches, a Monte Carlo configuration integral (MCCI) integration of partition functions and a Monte Carlo direct simulation of the equilibrium constants (MCEC), employing four well-validated potential energy functions have been used to calculate Delta G degrees of R1. Excellent agreement is observed for these two methods. Although different potential energy functions give different stage-1 results for n <= 10, three high-level correction (HLC) terms, namely, a correction for the-potential energy difference of the global minima, another for the electronic excitation contribution, and a third based on calculating isomeric-rovibrational contribution, have been applied to mitigate deficiencies in the potential energy functions. For n = 2, good agreement has been found between the corrected simulation results and experimental data. For larger n, the more efficient MCEC method has been used. Finally, accurate Delta G degrees of R1 and thus Delta(f)G degrees of Al-n particles with n = 2-60 have been determined. This is the first example of the determination of nanoparticle free energies of formation.

In this paper we discuss the development, validation, and application of analytic potential energy functions for simulating Al nanoparticles. We consider six functions, the Ercolessi-Adams, Mei– Davenport, Sutton–Chen, and Streitz–Mintmire functions from the literature and the NP-A and NP-B functions from our group. We find that the NP-A and NP-B potential energy functions, which were fit to a set of 808 energies and geometries for Al clusters and nanoparticles and to a combination of theoretical and experimental data for three bulk phases of metallic Al, are more accurate for Al nanoparticles than are the functions from the literature, which were mainly (but not entirely) parameterized for the bulk. We have used the NP-B potential to simulate liquid Al nanodroplets to study the size dependence of their densities, thermal expansivities, and particle shapes. The nanoparticle densities were computed by first computing the volumes using overlapping van der Waals spheres. We then used the densities to compute the coefficient of thermal expansion for nano-Al droplets; this coefficient was found to increase with increasing particle size. We have also shown that particle shape is size dependent, with smaller particles being prolate spheroids.

Monte Carlo simulations were carried out to compute the Hildebrand solubility parameter and the internal pressure for n-hexane, benzene, and ethanol at a temperature of 303.15 K and for external pressures ranging from 0.1 to 300 MPa. In addition, the internal energy, molar volume, enthalpy of the liquid phase, and free energy, enthalpy, and entropy of solvation were calculated as a function of external pressure. For all three molecules, the solubility parameter is found to increase monotonically with increasing external pressure, while the internal pressure exhibits a maximum. The magnitude of the solvation free energy decreases monotonically as external pressure is increased and both enthalpic and entropic terms contribute to this decrease in solubility. Analysis of radial distribution functions indicates small structural changes in the liquid phase and differences between nonpolar and h ydrogen-bonding fluids in response to external pressure changes.

Electrode poisoning by CO is a major concern in fuel cells. As interest in applying computational methods to electrochemistry is increasing, it is important to understand the levels of theory required for reliable treatments of metal-CO interactions. In this paper we justify the use of relativistic effective core potentials for the treatment of PdCO and hence, by inference, for metal-CO interactions where the predominant bonding mechanism is charge transfer. We also sort out key issues involving basis sets and we recommend that bond energies of 17.2, 43.3, and 69.4 kcal/mol be used as the benchmark bond energy for dissociation of Pd2 into Pd atoms, PdCO into Pd and CO, and Pd2CO into Pd2 and CO, respectively. We calculated the dipole moments of PdCO and Pd2CO, and we recommend benchmark values of 2.49 and 2.81 D, respectively. Furthermore, we tested 27 density functionals for this system and found that only hybrid density functionals can qualitatively and quantitatively predict the nature of the sigma-donation/pi-back-donation mechanism that is associated with the Pd-CO and Pd2-CO bonds. The most accurate density functionals for the systems tested in this paper are O3LYP, OLYP, PW6B95, and PBEh.

Monte Carlo simulations are presented for two models of aluminum: an embedded-atom model and an explicit many-body model. Vapor/liquid coexistence curves are determined using Gibbs ensemble Monte Carlo simulations. The normal boiling points predicted by both models are somewhat higher (by about 10%) than the experimental value. Isothermal constant-stress simulations are used to simulate solid Al from 300 K to the triple point. The solid structures are at least metastable in the face-centered cubic configuration, and the specific heat is determined to be lower than the experimental value. The melting point for the embedded-atom model determined via thermodynamic integration along a pseudo-supercritical path is approximately 20% higher than the experimental value.