Prigogine theorem of minimum entropy production applied to the average-atom model

Thermodynamics of irreversible processes is applied to study the interaction of matter and a radiation field in non-local thermodynamic equilibrium within the framework of the average-atom model. The rate of entropy production of matter and the radiation field, in contact with a free electron reservoir in local thermodynamic equilibrium, is obtained using conjugates of the state variables. The average-atom one-electron populations are determined by minimizing the rate of entropy production at fixed electronic density, electronic temperature, and radiation field. Numerical results and comparisons with experiment for a photoionized iron plasma are presented and discussed. Our approach, which is based on first principles, can be used in a large variety of non-local thermodynamic equilibrium situations.