The statistical mechanical description of small systems staying in thermal equilibrium with an environment can be achieved by means of the Hamiltonian of mean force. In clear contrast to the reduced density matrix of an open quantum system, or the reduced phase space probability density function of a classical open system, the Hamiltonian of mean force does not only characterize the reduced state but additionally contains the full information about the thermodynamics of the considered open system. The resulting thermodynamic potentials all assume the form as the difference of the potentials for the total system and the bare environment in the absence of the system. In contrast to work as a mechanical notion, one faces several problems with the definition of heat which turns out to be largely ambiguous in the case of strong coupling between system and environment. We review the general theory of the thermodynamics of open systems in particular in view of strong coupling and illustrate it by several examples. The vagueness of heat is discussed in the context of the ambiguities in the definitions of a fluctuating internal energy and other fluctuating thermodynamic potentials.

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座谈会：强耦合下的统计力学和热力学：量子与经典

可以通过平均力的哈密顿量来获得与环境保持热平衡的小型系统的统计力学描述。与开放量子系统的简化密度矩阵或经典开放系统的简化相空间概率密度函数形成鲜明对比的是，平均力的哈密顿量不仅表征了还原态，而且还包含有关热力学的完整信息。被认为是开放系统。所得的热力学势均假定为整个系统的势与没有系统的裸环境的势之差。与作为机械概念工作相比，人们面临着热量定义的几个问题，在系统与环境之间强耦合的情况下，热量的定义大体上是模棱两可的。我们特别从强耦合的角度回顾开放系统热力学的一般理论，并通过几个示例进行说明。在模糊的内部能量和其他波动的热力学势的定义的模糊性的背景下讨论了热的模糊性。