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【摘要】

Motility-induced phase separation (MIPS), exhibited by a system of active Brownian particles with repulsive interaction has been extensively studied during the last decade. In this talk, we will discuss the effect of a crucial parameter, namely the softness of the inter-particle repulsion, on MIPS. Using model of active Brownian discs interacting via a generalized Weeks-Chandler-Andersen (WCA) potential, we found that increasing the particle softness leads to a delayed transition to the MIPS state. Furthermore using a different form of inter-particle interaction -- a harmonic potential that allows a larger particle overlap, we found that interaction softness destabilizes the MIPS phase, forming a spanning porous cluster. This soft limit can also be reached by increasing particle motility over a critical value at which the system exhibits all of the characteristics of a standard percolation transition. We extended our study to study a binary mixture of hard and soft particles -- we found that apart from the transitions seen for the homogeneous system, there is a complex structure formation within the MIPS state, which depends on the relative softness of the binary system. With these additional phases, the phase-diagram of repulsive active particles appears to be more complex than previously perceived.