Analysis of the transverse and the longitudinal pseudodiffusion of CO2 in sub- and supercritical states: A molecular-dynamics analysis

Abstract

We have performed molecular-dynamics simulations of CO(2) system along the gas-liquid coexistence curve and on the isochore 94.22 cm(3) mol(-1) (which corresponds to the critical isochore). The calculation has been carried out in order to analyze the diffusion of CO(2) and particularly to figure out how the diffusion coefficient may be decomposed along the molecular axes. This makes it possible to analyze the anisotropy of the diffusion along these axes and to shed light on the microscopic changes which accompany such behavior. This anisotropy is traced back to the effect of the translation-rotation coupling (TRC) along the molecular axes. Along the liquid-gas coexistence curve, the pseudolongitudinal diffusion is found to be more rapid than the transverse one. The opposite trend is found along the isochore 94.22 cm(3) mol(-1). The role of the local structure was explored by calculating intermediate scattering function and the autocorrelation functions for the forces acting along the molecular axes. It is shown that the strength of the TRC effect is correlated to the difference between the relaxation times of the local structure, that of the reorientation along the molecular axes, and that of the translational motion. The analysis of the correlation time and the average mean square force along the longitudinal and transverse directions confirms the anisotropy of the local environment that determines the translational dynamics of a molecule.

Structure and dynamics of liquid CS2: Going from ambient to elevated pressure conditions

“…Nevertheless, it is known that recently alternative methods, based on modern computational tools, have been developed in order to extract in details the 3dimensional (3D) microstructure of the molecules in the liquid using the available scattering data. Such techniques, like Reverse Monte Carlo (RMC) 79 [94] and empirical potential structure refinement (EPSR) 80,81 , have been used in previous studies of several liquid systems to depict the 3D local structure around the molecules. Table I.…”

Comment on "An optimized potential for carbon dioxide" [J. Chem. Phys. 122, 214507 (2005)]

“…As there is widespread scientific interest in CO 2 , the model by Zhang and Duan [1] was employed for subsequent work [2,3,4,5,6]. It should be pointed out that no VLE data were published in [2,3,4,5,6].…”

“…As there is widespread scientific interest in CO 2 , the model by Zhang and Duan [1] was employed for subsequent work [2,3,4,5,6]. It should be pointed out that no VLE data were published in [2,3,4,5,6]. We recently tested the CO 2 model from Zhang and Duan [1] and found results that strongly deviate from these reported by Zhang and Duan [1].…”

Comment on "An optimized potential for carbon dioxide"

“…As there is widespread scientific interest in CO 2 , the model by Zhang and Duan 1 was employed for subsequent work 2,3,4,5,6 . It should be pointed out that no VLE data were published in 2,3,4,5,6 .…”