The non-bonded interactions incorporate multiple QM effects, such as electrostatics, induction, dispersion and exchange-repulsion, through effective non-bonded Coulombic and L-J interactions. In fixed point charge models there are many methods to derive partial charges from high-level QM calculations using a mixture of population analysis techniques, but ultimately no unique solution. While ab initio calculations yield high-quality charges they are often disregarded as being too computationally expensive and are substituted by a variety of semi-empirical QM based methods. These methods allow the rapid assignment of charges and are heavily parametrized in order to reproduce charges observed at higher levels of theory. For example, GAFF employs Mulliken charges produced from semi-empirical Austin Model 1 (AM1) calculations that are then subject to bond charge corrections (BCC) to better recreate experimental hydration free energies. The resulting electrostatic potential is then comparable to that calculated at the HF/6-31G * level which was used to parameterize the AMBER restrained electrostatic potential (RESP) charges. OPLS-AA, on the other hand, uses Cramer-Truhlar CM1A charges, and recently also included an AM1-BCC inspired localized BCC version of the OPLS-AA/CM1A FF that is available through the LigParGen server. It should also be noted that, as these semi-empirical QM calculations are performed in vacuum, they have to be modified to include polarization effects to make them suitable for condensed phase modelling. This is often performed via the inclusion of the BCC mentioned in the case of GAFF and OPLS, and/or in the form of charge scaling factors all of which are only used on neutral molecules.