Shape effects on the cluster spreading process of spin-crossover compounds analyzed within an elastic model with Eden and Kawasaki dynamics

Abstract

In this paper we study the growth properties of domains of low spin molecules in a high spin background in open boundary elliptically shaped spin crossover systems within the framework of the mechanoelastic model. The molecules are situated on a triangular lattice and are linked by springs, through which they interact. Elliptical shapes are chosen in order to allow an in-depth analysis of cluster shapes as a function of the local curvature at their starting point and the length of the interface between the two phases. Contrary to the case of rectangular and hexagonal shapes, where the clusters always start from corners, we find that for ellipses clusters nucleate from vertices, co-vertices or any other site. We apply and compare two kinds of dynamics, Edenlike and Kawasaki, in order to determine the stable shape of the clusters and the most probable starting points. We show that the wetting angle for small clusters is somewhat higher than π/2 and approaches this value only for large clusters. The stability of clusters is analyzed by comparing the Gibbs free energy to the elastic energy in the system and is discussed as a function of the cluster size, curvature of the starting place and temperature.

Effect of intermolecular interactions on the nucleation, growth, and propagation of like-spin domains in spin-crossover materials

“…At this stage, it is worth considering the shape of the HS/LS interfaces, although this point was elucidated recently [34][35][36] in the case of a circularly lattice where the propagation of the HS/LS interface has shown that, for small LS domains, the radial interface is more stable until it reaches the midregion of the circular lattice where it lines up before coming back to the radial shape in the second half of the lattice. Though such observations are not totally found in the simulation reported above due to the difference in the lattice geometry, it is worth noting that the shape of the HS/LS interface might be simply reduced to a problem of optimization of the interface length where the system shape plays a crucial role due to the boundary conditions.…”

“…It is considered that the remarkable nucleation, growth, and propagation process shown in Fig. 1(c) and their impact on the displacement of molecules reflect the macroscopic volume change, which is an important feature of the SCO materials [20,26,35,36,38]. Therefore, the deformation is an important parameter to emphasize whose its spatial distribution merits closer examination.…”

Cluster evolution in molecular three-dimensional spin-crossover systems

“…This necessitated the elaboration of new models, which could account not only for the macroscopic phenomena, but also to provide insight into what happens inside a given sample when the transition proceeds. The new class of mechanoelastic models [16,17] implies the realistic premise that the interactions have their origins principally in the different molecular sizes of LS and HS molecules. Within this framework, it is possible to simulate and visualize the evolution of clusters from edges or corners in accordance with experimental observations.…”

Spatially Resolved Investigation and Control of the Bistability in Single Crystals of the [Fe(bbpya) (NCS)2] Spin Crossover Complex

“…This behavior was considered from the early stages of SCO research, [2][3][4] but it was first explicitly demonstrated using single crystal X-ray diffraction only in 2004. [5][6] Recently, these phenomena have been studied in detail by optical microscopy in some SCO crystals and several theoretical models [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] have also been proposed to describe the experimental observations.…”