The Parr-Pearson concept of absolute hardness has long afforded insightful means for assessing chemical reactions.  Its definition has been associated with second derivative of the energy of a system with respect to the number of electrons in that system.  The resulting concept of hardness is then applied to atoms and functional groups within materials.  However, when it comes to developing models for atomistic simulations, the problem is turned inside out: What is meant by the energy of an atom in a molecule or material is defined first, and the question of what an appropriate concept of hardness is asked second.  The fragment Hamiltonian model provides a concept of hardness so arrived at and further asserts that that concept is associated with the first derivative of a variable that I call ionicity.  The ionicity is the variable that serves to describe metals.

Concepts of fragment hardness and ionicity in atomistic models of materials

243rd National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.