Field theoretical approach to the liquid state. Elements of comprehension of the role of the ideal entropy

In a series of papers we have introduced a field theoretical approach to describe the liquid state. The formalism introduces a simple Hamiltonian which includes the ideal gas free energy and the standard interaction potential between particles coupling the fields. In this paper, we discuss the role and the importance of the ideal term in this formalism. We compare our approach to the standard liquid state theory and another approach based on a field description, the density functional theory where an identical functional appears. The comparison shows that field theory sheds new light on the role of the ideal entropy an aspect which is traditionally discarded in favor of a viewpoint focusing on the interaction potential.