Intermolecular Structure and Collective Dynamics of Supercritical Fluoroform Studied by Molecular Dynamics Simulations

Abstract

The density dependence of the local structure and of collective dynamics of a polar fluid fluoroform along an isotherm at a temperature of 1.03 T(c), in the near-critical (NC) region, were studied by classical molecular dynamics (MD) simulations. In the case of local structure we focus on local density inhomogeneities and on orientational pair correlations that are relevant to dielectric properties and light scattering intensities. Our results show that the density dependence of the frequency shifts of fluoroform ν(2) and ν(3) modes correlates well with that of intermolecular dipole-dipole interactions. Our study of collective dynamics deals with dipole and polarizability anisotropy relaxation, experimentally accessible through far-infrared absorption, depolarized light scattering, and optical Kerr effect. Our MD simulations were performed using an all-atom nonpolarizable potential model of fluoroform. Contributions of induced dipoles to dielectric properties were included using first-order perturbation theory, and this approach was also used to include interaction-induced contributions to polarizability anisotropy relaxation. For interactions involving induced dipoles, we calculated and compared the results of a distributed polarizability model to a model with a single polarizable site located at the center-of-mass. Using a projection scheme that allows us to identify the contributions from different relaxation mechanisms, we found that dipole relaxation is dominated by collective reorientation, while in the case of polarizability anisotropy, relaxation processes related to translational dynamics make a major contribution over most of the fluid density range. The dielectric properties of fluoroform in the NC region were calculated and compared to the corresponding measurements. We found the dielectric constant and the far-infrared absorption spectrum to be in good agreement with experiments.

Role of Red-Ox Cycle in Structural Oscillations and Solvation Dynamics in the Mitochondria of a Live Cell

“…Finally, we discuss solvation dynamics of CPM in mitochondria of normal breast cell MCF-10A and peri-nuclear region of breast cancer cell, MCF-7. Solvation dynamics − controls dynamics of polar reactions. The average solvation time (<τ s >) in MCF-10A and MCF-7 cell is 850 and 1400 ps, respectively.…”

“…One of the longstanding goals of ultrafast spectroscopy is to understand the dynamics in different locations in a living system (e.g., in different organelles inside a living cell). In recent years, there have been extensive applications of large-scale computer simulations − and ultrafast spectroscopy − to study dynamics in confined systems (in particular, of water molecules). The computer simulations provide high spatiotemporal resolution to describe dynamics in different molecular layers around a biomolecule. − The ultrafast experiments provide high temporal resolution with little or no spatial resolution.…”

“…In recent years, there have been extensive applications of large-scale computer simulations − and ultrafast spectroscopy − to study dynamics in confined systems (in particular, of water molecules). The computer simulations provide high spatiotemporal resolution to describe dynamics in different molecular layers around a biomolecule. − The ultrafast experiments provide high temporal resolution with little or no spatial resolution. Confocal microscopy provides very high spatial resolution.…”

Simulations of the OKE Response in Simple Liquids Using a Polarizable and a Nonpolarizable Force Field

“…This contrasts with their earlier results, where they showed that for the highly polarizable CS 2 molecule, the correlation function obtained with the F-MDID method differs significantly from the one obtained with the 1-MDID method. , What’s more, they showed that for highly polarizable molecules, like CS 2 , the iterative method for solving the DID equations is divergent, and thus another solving method is needed. In a recent paper on the system of low polarizability fluoroform molecules at different densities, the authors compared the 1-ADID and 1-MDID methods and concluded that use of the more detailed 1-ADID method becomes important at liquid densities for predicting the different contributions to the OKE signal; however, the total signal is almost the same for both methods . In another study, performed for benzene and hexafluorobenzene molecules, they have compared the F-MDID and F-ADID approaches and showed that the latter gives results closer to the experiment .…”

“…In a recent paper on the system of low polarizability fluoroform molecules at different densities, the authors compared the 1-ADID and 1-MDID methods and concluded that use of the more detailed 1-ADID method becomes important at liquid densities for predicting the different contributions to the OKE signal; however, the total signal is almost the same for both methods. 49 In another study, performed for benzene and hexafluorobenzene molecules, they have compared the F-MDID and F-ADID approaches and showed that the latter gives results closer to the experiment. 50 In that paper, they have used atomic polarizabilities being simply one-sixth of the molecular polarizability and did not take into account the intramolecular interactions between the polarizable sites.…”