meaning that the behavior in the slowly-varying density regions is the same. Several suggestions explaining the reduction in the overbinding in GGA functionals have been put forward, the simplest of which is: (i) GGA functionals favor reduced density gradients, s ∝ | ▽ n|/n 4/3 ; (ii) the volume of space with large s values scales with the free surface area, where "surface" may represent both a solid surface and the surface of molecules and atoms; (iii) a system with a molecule bound on a solid surface exposes less surface (and therefore has less volume with large s values) than do the reference systems of a clean solid surface and a gas phase molecule; (iv) consequently, the adsorption system is destabilized over the reference system. That is, the attachment will become less attractive and the binding energy will become less negative when using a GGA.