Interaction energy concept

The idea of interaction energy is based on the Born-Oppenheimer (clamped nuclei, see eq. (6.4)) approximation. Let us define interaction energy at the configuration R of the nuclei as 

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The idea that unsymmetrical molecules will orient at an interface is now so well accepted that it hardly needs to be argued, but it is of interest to outline some of the history of the concept. Hardy [74] and Harkins [75] devoted a good deal of attention to the idea of force fields around molecules, more or less intense depending on the polarity and specific details of the structure. Orientation was treated in terms of a principle of least abrupt change in force fields, that is, that molecules should be oriented at an interface so as to provide the most gradual transition from one phase to the other. If we read interaction energy instead of force field, the principle could be reworded on the very reasonable basis that molecules will be oriented so that their mutual interaction energy will be a maximum. 

This concept implies low interaction energies between the segments consequently, the essential determinant of the position of the redox potentials must be the structure of the so-called effectively conjugated segments (ECS). 

Let us show some possible explanations of such experimental data based on the application of spatial-energy concepts. As before we will consider the approximate equality of effective energies of interacting subsystems as the main condition for the formation of stable structure based on the following equation ... 

In natural waters organisms and their abiotic environment are interrelated and interact upon each other. Such ecological systems are never in equilibrium because of the continuous input of solar energy (photosynthesis) necessary to maintain life. Free energy concepts can only describe the thermodynamically stable state and characterize the direction and extent of processes that are approaching equilibrium. Discrepancies between predicted equilibrium calculations and the available data of the real systems give valuable insight into those cases where chemical reactions are not understood sufficiently, where nonequilibrium conditions prevail, or where the analytical data are not sufficiently accurate or specific. Such discrepancies thus provide an incentive for future research and the development of more refined models. 

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