Density functional theory relation with conventional

On the other hand, the pure density functional theory provides a conceptual framework that has proven to be very useful to establish expressions that are closely related with chemical concepts, and to rationalize, through the values associated with them, the behavior of a wide variety of chemical species under different circumstances [20]. In order to calculate the values of these quantities, it has become common practice to make use of conventional molecular orbital theory [21-26]. Thus, this procedure allows one to transform the relevant information contained in the wavefunction, into chemically meaningful results, through the bridge provided by pure density functional theory. 

McCoy and coworkers [52] have neralized this density functional scheme to describe the crystallization of polymers. In this approach the structure of the liquid is provided by PRISM theory. Three conditions are necessary in order to ensure equilibrium between the solid and liquid phases. (1) temperature equality, (2) equality of the chemical potentials t, and (3) inessure equality. Because these conditions it is more convenient to work with the Grand potential W rather than the more conventional Helmholtz free energy A. W is related to... 

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