Fast Algorithm for Diluted Dipolar Systems with and without External Field

D.A. MARTIN; T.S. GRIGERA; V.I. MARCONI

Congreso; STATPHYS; 2019

We present  recent results on numerical simulations of Diluted Dipolar Spheres (DDS) in the NVT ensemble, with and without [Phys. Rev. E 99, 022604 (2019)] an external field. We  performed a Monte Carlo  speed-up algorithm, "Cluster Move Monte Carlo" (CMMC). Our system of strongly interacting dipolar  particles tend to self-organize into intrincated structures. We  found and characterized several regimes. CMMC combines typical single particle rotation and translation with  movements of  particle  groups, in such a way that detailed balance is preserved. The algorithm is easy to implement and it speeds-up simulations by a factor 10 to 100 (compared to traditional Monte Carlo), depending on density and temperature. It is also faster than other speed-up algorithms. It is efficient for truncated potentials  but also when Ewald sums are used. It may be useful for other, related, on-lattice and off-lattice systems. With the aid of CMMC, we study a set of positional, orientational, and thermodynamical observables, as a function of temperature and density.  We draw a regime diagram including simple-fluid, chain-fluid, ring-fluid, gel, and antiparallel columnar regimes. We later study how the regime diagram  of our system changes under external field.The study of DDS is relevant from the theoretical point of view, but can also be related to systems of technological interest, such as magnetic dipolar nanoparticles, for which, several applications have been proposed [J. Nanopart. Res. 5, 323 (2003)]. Nowadays, nanoparticles with large dipolar moments, comparable with the ones studied here, can be synthesized [Sci. Rep. 7, 9894 (2017)]. We mention briefly how our results can be related to reliable applications.