Accelerating the calculation of dipolar interactions in particle based simulations with open boundary conditions by means of the P2NFFT method

Abstract Magnetic gels are soft elastic materials consisting of magnetic particles embedded in a polymer network. Their shape and elasticity can be controlled by an external magnetic field, which allow for many applications, e.g., in engineering and biomedicine. Due to their inherent complexity, computer simulations are a commonly used tool to study these materials. A well-known bottleneck for the numerics is the demanding calculation of dipolar interactions. For periodic boundary conditions there exist established algorithms, however, at the expense of restricting the way in which the gels can deform in an external magnetic field. Moreover, the magnetic properties depend on the sample shape, ruling periodic boundary conditions where the gel has no boundary out entirely for some research questions. In this article we will employ the recently developed dipolar variant of the P 2 NFFT method for open boundary conditions with an N log ⁡ N scaling in the number of particles, rather than the expensive N 2 scaling of a direct summation of pair forces. The dipolar P 2 NFFT method has been implemented within the ScaFaCoS library. The molecular dynamics software ESPResSo has been extended to make use of the library. After a short summary of the method, we will discuss its relevance for studying magnetic soft matter systems. A particular focus is put on developing a tuning strategy to reach the best performance of the method at a predefined accuracy, and lastly we will apply the method to a magnetic gel. Here, adapting the method to the change in shape of the gel during the course of a simulation is of particular importance.