The liquid structure of tetrachloroethene: Molecular dynamics simulations and reverse Monte Carlo modeling with interatomic potentials

Abstract

The liquid structure of tetrachloroethene has been investigated on the basis of measured neutron and X-ray scattering structure factors, applying molecular dynamics simulations and reverse Monte Carlo (RMC) modeling with flexible molecules and interatomic potentials. As no complete all-atom force field parameter set could be found for this planar molecule, the closest matching OPLS-AA intra-molecular parameter set was improved by equilibrium bond length and angle parameters coming from electron diffraction experiments [Karle, I. L.; Karle, J. J. Chem. Phys. 1952, 20 63]. In addition, four different intra-molecular charge distribution sets were tried, so in total, eight different molecular dynamics simulations were performed. The best parameter set was selected by calculating the mean square difference between the calculated total structure 2 factors and the corresponding experimental data. The best parameter set proved to be the one that uses the electron diffraction based intra-molecular parameters and the charges q C =0.1 and q Cl =-0.05. The structure was further successfully refined by applying RMC computer modeling with flexible molecules that were kept together by interatomic potentials. Correlation functions concerning the orientation of molecular axes and planes were also determined. They reveal that the molecules closest to each other exclusively prefer the parallel orientation of both the molecular axes and planes. Molecules forming the first maximum of the center-center distribution have a preference for <30 º and >60 º axis orientation and >60 º molecular plane arrangement. A second coordination sphere at ~11 Å and a very small third one at ~16 Å can be found as well, without preference for any axis or plane orientation.

Transferable Potentials for Chloroethenes: Insights into Nonideal Solution Behavior of Environmental Contaminants

“…Figure 6D results are in excellent agreement with the ED_MID center of mass RDF plot. As depicted by Gereben and Pusztai work, 15 a shoulder is observed between 3.9 and 4.1 Å for the ED_MID charge sets and our simulation results also confirm this noteworthy feature at 3.95 Å, as shown in Figure 6D. In addition, the location of the first coordination shell peak is at 6.35 Å approximately as compared to 6.3 Å in their work.…”

“…The blue and green color lines represent results obtained from ED_Cl and ED_MID MD simulations in the work by Gereben and Pusztai. 15 Red color lines represent results obtained from the force field developed in the present work.…”

“…Figure 6A–D shows RDFs for carbon–carbon (C–C), carbon–chlorine (C–Cl), chlorine (Cl)–chlorine (Cl), and center of mass separations for tetrachloroethylene molecule at 293 K. All of the RDF plots were compared with the results obtained from molecular dynamics simulations carried out in Gereben and Pusztai work. 15 In Gereben and Pusztai work, 15 LJ parameters are taken from OPLS-AA 17 and used in combination with two different sets of partial atomic charges (ED_MID and ED_Cl). In the C–C and C–Cl plots, the location of the first coordination shell peak is at 6 and 4.95 Å, respectively, which is in good agreement with ED_MID and ED_Cl simulation data.…”

“…All RDF analyses from our force field simulations are in good agreement with Gereben and Pusztai work. 15 However, the Gereben and Pusztai 15 included intramolecular Cl–Cl terms in their plot along with intermolecular terms (Figure 6C). This leads to two sharp peaks at short distances and distorts the intermolecular RDF.…”

“…In some of the adsorption studies, − the C and H interaction parameters were taken from previous Monte Carlo studies that reported good heat of adsorption of methane in zeolites. , The parameters for chlorine were derived from Lennard-Jones (LJ) parameters of argon as Ar and Cl have similar atomic radii and polarizabilities . As such, there are no force field developed specifically for chloroethenes, but some studies , have used optimized potential for liquid simulations (OPLS)-type force field for chloroalkenes. Dellis et al examined the accuracy of OPLS force field for cis and trans -1,2-dichloroethene compounds.…”