Thermodynamic analysis of a molecular quantum Otto heat engine based on electronic energy state of ethylene

One of the most paradigmatic models for exploring the performance of quantum heat engines at the nanoscale is represented by quantum Otto cycle. Here, a quantum Otto engine is designed based on the two-level electronic system composed from an ethylene molecule. In the considered engine the working substance is defined by the ground state (S₀) and the first excited state (S₁) of the ethylene molecule. The energies of this system are calculated using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT). An electric field was used as the thermal reservoir in high temperature in isochoric strokes and isothermal steps was set up by adsorption and emission of photons by the molecule that transport the molecule between ground and excited states. The differences in the ground state-excited state gap due to the application of electrical field is the source of work and can be considered as tunable parameter of the engine. considered engine was demonstrated quantitatively by evaluating the net-work, the exchanged heat, thermodynamics efficiency and other thermodynamics properties. The results show that the π system of ethylene, characterized by a tunable energy gap, allows us to construct a thermal engine operating within a specific frequency range of the thermal reservoirs. the efficiency varies nonlinearly with the work amount. Furthermore, it was observed that in specific values for electrical field, the proposed device transfers heat from cold reservoir to the hot bath and can be used as quantum refrigerator to decrease temperature of cold bath. From the results of this study, we can suggest the using of simple organic molecules as the building blocks for molecular-scale quantum thermal machines or quantum refrigerators for release work or transfer heat in order to cooling purposes.