One of the strongest examples is the lack of molecular polarization effects alongside permanent electrostatics interactions. Real molecules, if treated quantum mechanically, have the ability to respond to their environment and adjust their distribution of electrons throughout the molecule. Whether it is in response to other nonbonded fragments or externally applied fields, standard force fields must somehow incorporate this contribution into the aforementioned terms in order to maintain the correct total interaction energy. Additionally, charge penetration effects that incorporate overlap and electron diffusivity are also not included in the Coulombic terms, neglecting an attractive force between two atoms (in the small overlap regime) due to electrons not being point-like objects as compared to their partnered nuclei.