Quantum self-similarity measures as QSAR descriptors

Sometimes, drug-receptor interactions are simple enough to be accurately characterized by a single parameter linear relationship. This was a general fact in early QSAR models, in which descriptors such as log P or Hammett a were used as sole parameters. In this kind of systems, therefore, it is not necessary to use such a sophisticated QSAR approach as detailed in chapter 4. A simpler method can be constructed by neglecting the off-diagonal similarity matrix while using only the diagonal elements, constituting the so-called quantum self-similarity measures (QS-SM). This simplification avoids the problem of selecting a molecular alignment, because the compared electron distributions belong to the same molecule, so the alignment is irrelevant. This new approach also permits, after a subsequent manipulation, the treatment of molecular fragments within the quantum similarity framework.