Flenner Elijah, Szamel Grzegorz
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
Phys Rev E. 2020 Aug;102(2-1):022607. doi: 10.1103/PhysRevE.102.022607.
Active matter systems are driven out of equilibrium at the level of individual constituents. One widely studied class are systems of athermal particles that move under the combined influence of interparticle interactions and self-propulsions, with the latter evolving according to the Ornstein-Uhlenbeck stochastic process. Intuitively, these so-called active Ornstein-Uhlenbeck particle (AOUP) systems are farther from equilibrium for longer self-propulsion persistence times. Quantitatively, this is confirmed by the increasing equal-time velocity correlations (which are trivial in equilibrium) and by the increasing violation of the Einstein relation between the self-diffusion and mobility coefficients. In contrast, the entropy production rate, calculated from the ratio of the probabilities of the position space trajectory and its time-reversed counterpart, has a nonmonotonic dependence on the persistence time. Thus, it does not properly quantify the departure of AOUP systems from equilibrium.
活性物质系统在个体组分层面上处于非平衡状态。一类被广泛研究的是无热粒子系统，这些粒子在粒子间相互作用和自推进力的共同影响下运动，其中自推进力根据奥恩斯坦 - 乌伦贝克随机过程演化。直观地说，对于更长的自推进持续时间，这些所谓的活性奥恩斯坦 - 乌伦贝克粒子（AOUP）系统离平衡态更远。从数量上看，这通过不断增加的等时速度相关性（在平衡态中是平凡的）以及自扩散系数和迁移率系数之间对爱因斯坦关系的不断违反得到证实。相比之下，根据位置空间轨迹及其时间反转对应物的概率之比计算出的熵产生率对持续时间具有非单调依赖性。因此，它不能恰当地量化AOUP系统偏离平衡的程度。
