Cluster evolution in molecular three-dimensional spin-crossover systems.

The nucleation and growth properties of domains of molecules of the same state in openboundary three-dimensional (3D) spin-crossover systems of various shapes are discussedwithin the framework of the mechanoelastic model. The molecules are situated on face-centered-cubic lattices and are linked by springs through which they interact. Monte Carlosimulations imply that clusters nucleate from corners in the case of systems having well-developed faces and from kinks in the case of spherical samples, in accordance with availableexperimental data. In addition, a method to characterize the cooperativity in these systems isproposed, which by scanning the fluctuations in the 3D samples can be related directly topowder x-ray-diffraction experiments.

This work was supported by National Research Council (CNCS-UEFISCDI), Romania, Grant No. PN-II-RU-TE-2014-4-0987, by the Swiss National Science Foundation(Grant No. 200020-125175) and byGrants-in-Aid for ScientificResearch C (Grants No. 26400324 and No. 17K05508)and the ElementsStrategy Initiative Center for Magnetic Materials under the outsourcing project of MEXT of Japan.The numerical calculations have been performed on the rAMONa computer cluster of Alexandru IoanCuza University and were partly supported by the supercomputer center of ISSP of Tokyo University.