A chemical system at a given temperature will evolve to a configuration of maximum
absolute hardness, η, provided that the potential due to the nuclei, plus any external
potential and the electronic chemical potential
, remain constant. In terms of molecular orbital
theory, the highest value of η reflects the highest possible energy gap between the
lowest unoccupied and highest occupied molecular orbitals; this value correlates with
the stability (See: structural stability; electronic stability
) of a system.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook