Chapter 4: QM Based Modelling

Quantum mechanical calculations, and in particular semiempirical MO theory have now been applicable to large pharmaceutical datasets for more than a decade and can be used routinely for hundreds of thousands of compounds with modern hardware. This chapter reviews the direct use of quantum mechanical properties, such as the molecular electrostatic potential and local ionisation energy, electron affinity, polarizability, electronegativity and hardness together with the electron density to describe molecules without constructing atoms and bonds (and their properties) within the molecule. Many techniques are based on the local properties projected onto a molecular surface, but grid-based techniques can also be used.