Thermodynamic models formulated based on the Landau free-energy expansion are popular and well suited to studies involving properties of the ferro/para-electric transition,or near it.Indeed,the general nature of thermodynamics,from which the strength of the model is derived,allows a valid model to be constructed based on simple functional forms with parameters fitted to experiments,by passing the mechanistic complexity.Despite inaccuracy due to the neglect of fluctuations,this approach has been proven effective and powerful for recent research development of ferroelectrics in nanoscale.Efforts in some important works have recently faced much challenge,when free-energy contributions have to be incorporated to account for the presence of depolarization fields,surfaces and other defects.To minimize the problems with mechanistic obscurity,it is of paramount importance that the electromagnetics,mechanics and thermodynamics involved are accounted for explicitly and with full self-consistency.It is important that the free-energy functional of nanoscale ferroelectric systems,such as ferroelectric thin films(FTF),bilayers(FB),superlattices(FS),nanowires(FNW),nanotubes(FNT) and tunneling junctions(FTJ) etc.,must be derived thermodynamically from first principles. Thermodynamic models formulated based on the Landau free-energy expansion are popular and well suited to studies involving properties of the ferro / para-electric transition, or near it.Indeed, the general nature of thermodynamics, from which the strength of the model is derived , allows a valid model to be constructed based on simple functional forms with parameters fitted to experiments, by passing the mechanistic complexity. Graduate inaccuracy due to the neglect of fluctuations, this approach has been proven effective and powerful for recent research development of ferroelectrics in nanoscale . Efforts in some important works have recently faced much much challenge, when free-energy contributions have to be incorporated to account for the presence of depolarization fields, surfaces and other defects. To minimize the problems with mechanistic obscurity, it is of paramount importance that the electromagnetics, mechanics and thermodynamics involved are explicitly for and with full self-consistency .It is important that the free-energy functional of nanoscale ferroelectric systems, such as ferroelectric thin films (FTF), bilayers (FB), superlattices (FS), nanowires (FNW), nanotubes (FNT) and tunneling junctions (FTJ) etc ., must be derived thermodynamically from first principles.