Exchange-correlation analytic properties

Although the exact functional xc[Pa. Ppl remains an enigma, many of its analytic properties, ranging from obvious to subtle, are known [74]. For any possible electron densities, the exchange energy is strictly negative, while the correlation energy is nonpositive ... 

For a DCL sensor of this kind, the information about the analyte is distributed over the entire spectrum. The spectrum therefore represents a fingerprint of the analyte. To correlate the spectral changes with the analyte properties of interest (identity, quantity, purity), it is advantageous to use multivariate analyses techniques. In this regard, a DCL sensor is related to sensor arrays (1, 2]. However, contrary to sensor arrays with independent sensor units, a DCL sensor is comprised of compounds that are connected by exchange reactions. Furthermore, the various sensors of an array have to be analyzed separately, whereas a single UV-Vis or fluorescence measurement is sufficient for a DCL sensor. 

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