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Adsorption and separation of Xe/Kr are significant for making high-density nuclear energy environmentally friendly and for meeting the requirements of the gas industry. Enhancing the accuracy of the adsorbate model for describing the adsorption behaviors of Xe and Kr in MOFs and the efficiency of the model for predicting the separation potential (SP) value of Xe/Kr separation in MOFs helps in searching for promising MOFs for Xe/Kr adsorption and separation within a short time and at a low cost. In this work, polarizable and transferable models for mimic Xe and Kr adsorption behaviors in MOFs were constructed. Using these models, SP values of 38 MOFs at various temperatures and pressures were calculated. An optimal neural network model called BPNN-SP was designed to predict SP value based on physical parameters of metal center (electronegativity and radius) and organic linker (three-dimensional size and polarizability) combined with temperature and pressure. The regression coefficient value of the BPNN-SP model for each data set is higher than 0.995. MAE, MBE, and RMSE of BPNN-SP are only 0.331, −0.002, and 0.505 mmol/g, respectively. Finally, BPNN-SP was validated by experiment data from six MOFs. The transferable adsorbate model combined with the BPNN-SP model would highly improve the efficiency for designing MOFs with high performance for Xe/Kr adsorption and separation. [ABSTRACT FROM AUTHOR]

Abstract: We report a molecular dynamics simulation of liquid water using the SWM4-NDP polarizable water model that belongs to the class of Drude oscillator type models. Generally, parameterisation protocols currently used for this type of models implicitly assume the validity of point-dipole approximation for the induced dipole (where the response of the dipole to the external field should depend only on the value of polarizability but not on the actual values of the charge or spring constant of the Drude oscillator). Therefore, possible dependency of the model results from the Drude charge/spring constant is often neglected. However, we show in this paper that the point-dipole approximation condition is actually not satisfied for a range of Drude oscillator parameters; that leads to a significant dependency of the obtained results from the particular choice of the Drude charge/spring constant. We analyzed the influence of the Drude charge value on the main macroscopic properties of water given by the SWM4-NDP water model (including density, static dielectric constant, self-diffusion constant, and surface tension). Our results show that (in general) the properties of model water do depend on the Drude charge value. We also provide an estimate for the Drude charge value (−10e) above which the point-dipole limit is achieved with good accuracy. In this paper we also discuss the differences in the convergence behaviour of different model water properties. Based on the obtained results we developed a new re-parameterised version of the SWM4-NDP model (SWM4-NDP10e) where the point-dipole limit condition is satisfied. We show that the model reproduces well important macroscopic as well as microscopic properties of water at ambient conditions. [Copyright &y& Elsevier]

Abstract: We calculated bulk properties of polarizable SWM4-NDP water model at elevated temperature and pressure. Density, self-diffusion coefficient, static dielectric constant and local ordering of water molecules are calculated for different temperatures (298–363K) and pressures (1, 100, and 690bar). The simulation results show that these properties are well reproduced by the SWM4-NDP model with discrepancies less than 7% from the experimental values in all the range of thermodynamic conditions considered. This is very encouraging since it proves the applicability of SWM4-NDP model for simulations of the systems under harsh conditions, thus the model can be used in many oil industry and environmentally related studies. [Copyright &y& Elsevier]

Recently, many polarizable force fields have been devised to describe induction effects between molecules. In popular polarizable models based on induced dipole moments, atomic polarizabilities are the essential parameters and should be derived carefully. Here, we present a parameterization scheme for atomic polarizabilities using a minimization target function containing both molecular and atomic information. The main idea is to adopt reference data only from quantum chemical calculations, to perform atomic polarizability parameterizations even when relevant experimental data are scarce as in the case of electronically excited molecules. Specifically, our scheme assigns the atomic polarizabilities of any given molecule in such a way that its molecular polarizability tensor is well reproduced. We show that our scheme successfully works for various molecules in mimicking dipole responses not only in ground states but also in valence excited states. The electrostatic potential around a molecule with an externally perturbing nearby charge also exhibits a near-quantitative agreement with the reference data from quantum chemical calculations. The limitation of the model with isotropic atoms is also discussed to examine the scope of its applicability. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Folding and unfolding of β-peptides has been studied extensively by molecular dynamics (MD) simulation in the past decade. In these simulations, a non-polarizable model for the solvent (mostly methanol) was used. This work has investigated the effect of using a polarizable methanol solvent model upon the folding equilibrium of β-peptides. Thirteen MD simulations covering a total simulation length of 1.25 µs for three differently folding β-peptides were analyzed. The agreement with experimental data was slightly improved by applying the polarizable solvent. In the polarizable solvent, helical structures, which have a large dipole moment, are stabilized, while no obvious effect was detected in the simulations of peptides that have a hairpin structure as the dominant fold. The introduction of electronic polarizability into the solvent model appears of importance to a proper description of folding equilibria if these are determined by competing solute conformations that have different dipole moments. [ABSTRACT FROM AUTHOR]

A polarizable model for simulation of liquid methanol, compatible with the COS/G2 water model, has been developed using the Charge-on-Spring (COS) technique. The model consists of three point charges, with one polarizable center on the oxygen atom. The Lennard–Jones parameters on the oxygen atom together with the molecular polarizability were varied to reproduce the experimental heat of vaporization and density of liquid methanol at ambient conditions. We examined the energies of various methanol dimers in the gas phase and compared them with values obtained from ab initio calculations. The model was then used to study the thermodynamic, dynamic, structural, and dielectric properties of liquid methanol as well as of a methanol–water mixture. A microscopic picture of the structure of pure liquid methanol and of the methanol–water mixture is provided. Good agreement was found between the results from our model simulations and available experimental and ab initio calculation data. In particular, the experimental dielectric permittivity of 32 could be reproduced, which had been shown to be difficult when using nonpolarizable models. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1494–1504, 2006 [ABSTRACT FROM AUTHOR]