We performed ab initio molecule orbital (MO) calculations to obtain the stable states of the ions in ionic liquids (ILs), partial atomic charges, and scaling factors for a charge scaling. Then, MD ...simulations based on united-atom (UA) force field introduced a charge scaling were carried out in ILs. The partial atomic charges of ions in ILs were determined by using charges from electrostatic potentials using a grid based method (CHelpG) from the B3LYP/6-311G(d,p) level wave function for cations B3LYP/6-311+G(d) one for anions. The scaling factors for C2C1Im, TFSA and FSA were considered from the dipole interactions. The calculated densities by MD simulation were reproduced the experimental values at 298K very well and there were errors within 5.0% deviations, because the partial atomic charges of the ions in ILs were scaling down and the coulomb interactions became weaker. Moreover, the self-diffusion coefficients of C2C1ImTFSA by MD simulation based on UA force field introduced a charge scaling showed the same order for the experimental values at 423K. Furthermore, the self-diffusion coefficients and the center-of-mass radial distribution functions in P2225TFSA at 298, 323, 348, 373, 398, and 423K were simulated. The calculated self-diffusion coefficients had a similar tendency with experimental ones. The position of first solvation shell withdrew about 0.25Å and its height became lower due to increase the temperatures. Both the first minimum position around 9–10Å and the second maximum position around 13–14Å also went away. This simulation result indicated that the intermolecular interaction strength between cations and anions became weaker with increasing temperature.
Abstract
Sophorolipids contain hydrophilic head groups at the ends of a long hydrophobic tail. As
a result, sophorolipids can self assemble into variety of structures in water. Atomistic
self ...assembly simulations of sophorolipids are performed in water. Two sophorolipids, oleic
acid sophorolipid and linolenic acid sophorolipid, differing in number of double bonds in
the hydrophobic tail are considered for this study. Long time self assembly simulations are
performed considering 1:3 lipid to water ratio by weight for both oleic and linolenic acid
sophorolipids. In addition to 1:3 ratio, long time self assembly simulations are also
performed with 1:1 and 1:2 ratios for linolenic acid sophorolipids. Distinctions in
structural arrangements of sophorolipid molecules in the self assembled configuration for
all the systems are investigated. The present study aims to provide structural insight into
the different self assembled configurations of sophorolipids in water.
Molecular dynamics simulation is conducted to microscopically study the effects of environmental pressure on the injection process of a fuel nanojet. The united-atom force field and Lennard-Jones ...12-6 potential are applied, which is validated by a single liquid droplet evaporation model against experiments. A gas-liquid-gas model represented by a simulation box for single droplet evaporation and an n-heptane nanojet injected into vacuum, lowly supercritical, and highly supercritical environments are investigated. Results indicate that at lowly supercritical conditions, the gas-liquid interface has been widened, and the interface tension still exists and the phase interface is detected. Only at highly supercritical conditions does the interface becomes sufficiently wide and a continuous phase transition without a distinct phase interface prevails. The most interesting conclusion from the molecular dynamics (MD) results is that the transition of a fluid from subcritical to supercritical states does not occur instantaneously when it goes across the critical point but is a gradual process that can be completed only when the temperature and pressure are sufficiently higher than the critical values. This microscopic analysis is well in accordance with the macroscopic measurements and observations in the literature.
Atomistic molecular dynamics simulations were carried out at equilibrium to calculate the shear viscosity of n-decane and n-hexadecane under ambient and high temperature-high pressure conditions. Two ...force fields, one using a computationally efficient united-atom (TrAPPE-UA) approach and another an all-atom (AA) approach (Tobias, Tu and Klein), were employed. Quantitative agreement with experimental data is obtained with the AA force field, whereas the UA model predicts the viscosity within 20-30% of the experiment. The intra- and inter-molecular structure of the fluid obtained from these two models is similar, pointing to the role of differences in their dynamical characteristics to the observed difference in the calculated viscosities.
Ionic liquids （ILs） have been widely used in separation, catalysis, electrochemistry, etc., and one of the most outstanding char- acteristics is that ILs can be tailored and tuned for specific tasks. ...In order to design and make better use of ionic liquids, the structures and properties relationship is indispensable. Both molecular dynamics and Monte Carlo simulations have been proved useful to understand the behavior of molecules at the microscale and the properties of the system. However, the quality of such simulations depends on force field parameters describing the interactions between atoms. All-atom （AA） or the unit- ed-atom （UA） force fields will be chosen because of the demand for more exact results or the lower computational cost, re- spectively. In order to make a systematic comparison of the two force fields, molecular simulations for four kinds of acyclic guanidinium-based ionic liquids （cations： （R2N）2C=N＋〈, anion： nitric or perchloric acid） were performed based on the AA and the UA force fields in this work. AA force field parameters were derived from our previous work （Fluid Phase Equilib., 2008, 272： 1-7）, and the UA parameters were proposed in this work. Molecular dynamics simulation results for the AA and UA force fields were compared. Simulation densities are very similar to each other. Center of mass radial distribution functions （RDFs）, site to site RDFs and spatial distribution functions （SDFs） were also investigated to depict the microscopic structures of the ILs.
