We propose a novel approach that allows efficient numerical simulation of systems consisting of flexible chain molecules. The method is especially suitable for the numerical simulation of dense chain systems and monolayers. A new type of Monte Carlo move is introduced that makes it possible to carry out large scale conformational changes of the chain molecule in a single trial move. Our scheme is based on the selfavoiding random walk algorithm of Rosenbluth and Rosenbluth. As an illustration, we compare the results of a calculation of mean-square end to end lengths for single chains on a two-dimensional square lattice with corresponding data gained from other simulations.

Over 14 000 porous, three-dimensional metal–organic framework structures are compiled and analyzed as a part of an update to the Computation-Ready, Experimental Metal–Organic Framework Database (CoRE MOF Database). The updated database includes additional structures that were contributed by CoRE MOF users, obtained from updates of the Cambridge Structural Database and a Web of Science search, and derived through semiautomated reconstruction of disordered structures using a topology-based crystal generator. In addition, value is added to the CoRE MOF database through new analyses that can speed up future nanoporous materials discovery activities, including open metal site detection and duplicate searches. Crystal structures (only for the subset that underwent significant changes during curation), pore analytics, and physical property data are included with the publicly available CoRE MOF 2019 database.

The extension of the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field to the ether, glycol, ketone, and aldehyde functionalities is presented. New parameters for the ether oxygen, the carbonyl carbon (ketones), the carbonyl methine (aldehydes), and a special intramolecular hydrogen-bond term were fitted to the vapor-liquid coexistence curves for selected one-component systems. Coupleddecoupled configurational bias Monte Carlo simulations in the Gibbs or grand canonical ensemble were used to compute the vapor-liquid coexistence curves for the neat systems of dimethyl ether, ethyl methyl ether, diethyl ether, dipropyl ether, diisopropyl ether, methyl tert-butyl ether, 1,2-ethanediol, 2-methoxyethan-1-ol, 1,2-dimethoxyethane, 1,3-propanediol, acetone, 2-pentanone, 2-octanone, acetaldehyde, pentanal, and octanal. Additional simulations were performed for the binary mixtures of diethyl ether + ethanol and acetone + hexane. Excellent agreement with experimental results was found with the mean unsigned errors being less than 1% for the critical temperatures and about 3% (ethers) and 1% (other) for the normal boiling temperatures. For the mixture of acetone + hexane at 328.15 K, a positive pressure azeotrope was found with x acetone azeo ) 0.71 in satisfactory agreement with the experimental result of 0.64. Additionally, the structures of hydrogenbonded aggregates were investigated for 1,2-ethanediol and 2-methoxyethan-1-ol, where the average hydrogenbond energies were found to be about -20 and -14 kJ mol -1 for inter-and intramolecular hydrogen bonds, respectively.

We have used the classical molecular dynamics technique to simulate the ordering of a water film adsorbed on an atomic model of a tip of a scanning tunneling microscope approaching a planar metal surface. For this purpose, we have developed a classical model for the water–substrate interactions that solely depends on the coordinates of the particles and does not require the definition of geometrically smooth boundary surfaces or image planes. The model includes both an electrostatic induction for the metal atoms (determined by means of an extended Lagrangian technique) and a site-specific treatment of the water–metal chemisorption. As a validation of the model we have investigated the structure of water monolayers on metal substrates of various topology [the (111), (110), and (100) crystallographic faces] and composition (Pt, Ag, Cu, and Ni), and compared the results to experiments. The modeling of the electrostatic induction is compatible with a finite external potential imposed on the metal. This feature is used to investigate the structural rearrangements of the water bilayer between the pair of scanning tunneling microscope electrodes in response to an applied external voltage difference. We find significant asymmetry in the dependence on the sign of the applied voltage. Another result of the calculation is an estimate of the perturbation to the work function caused by the wetting film. For the conditions typical for operation of a scanning tunneling microscope probe, the change in the work function is found to be comparable to the applied voltage (a few hundred millivolts).

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Hydrogen sulfide removal is a long-standing economic and environmental challenge faced by the oil and gas industries. HS separation processes using reactive and non-reactive absorption and adsorption, membranes, and cryogenic distillation are reviewed. A detailed discussion is presented on new developments in adsorbents, such as ionic liquids, metal oxides, metals, metal-organic frameworks, zeolites, carbon-based materials, and composite materials; and membrane technologies for HS removal. This Review attempts to exhaustively compile the existing literature on sour gas sweetening and to identify promising areas for future developments in the field.

The adsorption of the n-alkanes, ranging from butane to dodecane, in the zeolites silicalite and (all silica) mordenite has been studied in the zero coverage limit using computer simulations. The heats of adsorption, Henry coefficients, and distribution of the n-alkanes over the different zeolite channels are calculated. The calculated heats of adsorption are in good agreement with available experimental data. The calculated heats of adsorption in silicalite show a n unexpected alkane length dependence. The incremental heat of adsorption per carbon atom is larger for the longer alkanes than for the shorter alkanes. This observation is attributed to preferential adsorption of the longer alkanes in the straight channels of silicalite. Simulations of this type were made possible through the development of a novel Monte Carlo simulation technique which is orders of magnitude more efficient than the conventional simulation techniques.