Thermodynamics and phase transitions in dissipative and active Morse chains

We study the evolution of a simple one-dimensional chain of N=4 particles with Morse interactions and periodic boundary conditions which are imbedded into a heat bath creating dissipation and noise.The investigation is concentrated on thermodynamicproperties for equilibrium, near-equilibrium and far-equilibrium conditions. For the thermodynamic equilibrium, created by white noise andpassive friction obeying Einsteins fluctuation dissipation relation, we find a standard phase diagram.By applying active friction forcesthe system is driven to stationary non-equilibrium states, creating conditionswhere various self-sustained oscillations are excited. Thermodynamic quantities like energy, pressure and entropy are calculated near equilibrium, around a critical distance from equilibrium and far fromequilibrium. We observe maximal order (minimum entropy) in certainregion of the noise temperature, a phenomenon which is reminiscent ofstochastic resonance. With increasing distance from equilibrium new phases corresponding to the existence of several attractors of the dynamical stem appear.