Using DL_POLY to study the sensitivity of liquid structure to potential parameters

Abstract

. Using DL_POLY to study the sensitivity of liquid structure to potential parameters. Molecular Simulation, Taylor Francis, 2007, 32 (12-13) Two case studies are presented showing the local structure in liquids and how it responds to changes in the intermolecular potential. The idea is to use realistic and unrealistic potentials in order to determine the sensitivity of local liquid structure to potential parameters. The first case study concerns two families of modified water models. In the 'hybrid' family the hydrogen bond strength is reduced, but the geometry kept constant; in the second family the molecular geometry is changed by reducing the bond angle, keeping a constant molecular dipole moment. The local structure is measured by radial distribution functions, three dimensional probability distribution functions and three body angular correlations. The second case study concerns the ionic liquid dimethylimidazolium chloride ([C 1 mim]Cl). The effect of reducing the hydrogen bonding potential of the cations while maintaining their charge is examined.

Tetrahedral Ordering in Water: Raman Profiles and Their Temperature Dependence

“…For the same reason at high temperature f ( q , T ) becomes almost symmetric and unimodal with a maximum at about q = 0.50 that corresponds to the distribution typical of a Lennard-Jones molecular system . A further increase of ε OO by a factor 3 (hybrid s30) makes totally symmetric and unimodal also the low temperature distribution. These findings further confirm the rationalization of the SPC/E f ( q , T ) in terms of a mixture of ordered and disordered local domains and also suggest that the temperature dependence of the f ( q , T ) distributions increases with the extent of tetrahedral ordering.…”

“…The capability of water in forming tetrahedral configurations can be modulated by changing either the relative strength of dispersive interactions with respect to Coulombic interactions in the water potential (hybrid models) or the water geometry (bent models) as attempted in the recent past. − As an example, following a practice of the recent literature one can increase ε OO in eq to reduce the weight of the electrostatic contribution related to H-bond forces. A larger ε OO leads to larger repulsions, weaker H-bonds and more isotropic interactions and makes the systems more similar to a Lennard-Jones liquid. − The net result of the loss of anisotropy should imply a smoothing of the f ( q , T ) structure in the related MD outcomes. In Figure the results of the MD calculations performed on a modified potential in which ε OO was increased by a factor 1.5 (this is the hybrid s15 model in the notation of ref ) are plotted.…”

“…A larger ε OO leads to larger repulsions, weaker H-bonds and more isotropic interactions and makes the systems more similar to a Lennard-Jones liquid. − The net result of the loss of anisotropy should imply a smoothing of the f ( q , T ) structure in the related MD outcomes. In Figure the results of the MD calculations performed on a modified potential in which ε OO was increased by a factor 1.5 (this is the hybrid s15 model in the notation of ref ) are plotted. As expected, the loss of ordering capacity, following the modification of the potential, dramatically lowers the intensity of the high- q peak component.…”

Shielding of Ionic Interactions by Sulfur Dioxide in an Ionic Liquid

“…23,24 Computer simulations of ionic liquids have complemented the microscopic view provided by these experiments. [25][26][27][28][29][30] Several molecular dynamics (MD) simulations have been reported, especially for the wellknown systems based on 1-alkyl-3-methylimidazolium cations. (the structure of 1-butyl-3-methylimidazolium cation is depicted in Figure 1).…”

Shear Viscosity of the Ionic Liquid 1-n-Butyl 3-Methylimidazolium Hexafluorophosphate [bmim][PF6] Computed by Reverse Nonequilibrium Molecular Dynamics

“…However, a detailed understanding of the relation between structural and dynamic properties of ionic liquids is still missing, hampering the rational design of low-viscosity products. In recent years, molecular dynamics (MD) simulations – have been performed to obtain fundamental understanding of various properties of ionic liquids in the liquid bulk phase or at interfaces. MD methods have also been employed to compute the shear viscosity of different ionic liquids. – …”