The plastic and liquid phases of CCl3Br studied by molecular dynamics simulations

Abstract

We present a molecular dynamics study of the liquid and plastic crystalline phases of CCl 3 Br. We investigated the short-range orientational order using a recently developed classification method and we found that both phases behave in a very similar way. The only differences occur at very short molecular separations, which are shown to be very rare. The rotational dynamics was explored using time correlation functions of the molecular bonds. We found that the relaxation dynamics corresponds to an isotropic diffusive mode for the liquid phase, but departs from this behavior as the temperature is decreased and the system transitions into the plastic phase.

Comparison of the atomic level structure of the plastic crystalline and liquid phases of CBr2Cl2: neutron diffraction and reverse Monte Carlo modelling

“…4 for plastic and liquid CBr 2 Cl 2 ; only a slight difference can be noticed between the two phases. This statement was also true in the case of CBrCl 3 [6], supporting the strong resemblance between the two halomethane compounds. The pattern, in general, follows the one shown for CBrCl 3 : the 2:2 orientations are the most populous beyond 8 Å, as was observed for the whole family of CBr n Cl 4-n (n=0, 1, 2, 4).…”

“…This way, corner-to-corner (1:1); corner-to-edge (1:2); corner-to-face (1:3); edge-to-edge (2:2); edge-face (2:3); face-to-face (3:3) orientations may be distinguished. The clarity of this scheme permits its application to other systems consisting of tetrahedral molecules such as CCl 4 [3], CBrCl 3 [6] and CBr 4 [13]; it is also our intention here to compare our present results with these earlier works [3,6,13].…”

“…A common feature that makes these systems attractive is that an orientationally disordered crystalline phase -also called 'plastic crystal' -appears between the low-temperature ordered phase and the liquid phase [5,6,10]. In this special phase the molecular centres are located in a highsymmetry lattice (face centered cubic, body centered cubic or rhombohedral), but the molecules can rotate around their equilibrium position.…”

The structure of PX3 (X = Cl, Br, I) molecular liquids from X-ray diffraction, molecular dynamics simulations, and reverse Monte Carlo modeling

“…For the present study, we have adapted the construction that was developed for CXY 3 liquids 10 (for more examples, see Refs. [26][27][28]). The PX 3 trigonal pyramid (or, in other words, distorted tetrahedron) can be supplemented by a virtual atom, positioned where the lone electron pair of the P atom would be, to form a more regular tetrahedron; the resulting geometrical body is therefore very similar to a CXY 3 molecule.…”

Structural signatures of (two) characteristic dynamical temperatures in lithium metasilicate

“…While the case of alcali silicates is probably an extreme one, in the sense that the network of tetrahedra is extremely disordered due to the effect of alcali atoms on the network, the present approach can probably lead to interesting insights on the interplay between dynamics and order in other families of network forming systems which show different degrees of ordering, e.g. plastic glasses [25,31]. By monitoring the type and relative abundance of selected atoms at the vertices of tetrahedra the connection between dynamics and structure can be studied in detail and may allow to gain important insights in the nature of glassy behavior of complex systems.…”