Generalized gradient approximation relativistic form

As the hopes placed in the GEA did not materialize (in the non-relativistic case), one turned to the construction of generalized gradient approximations (GGA). These are based on the following philosophy (i) Use available exact results for atoms (x-only or on the basis of Cl calculations) and fit them to a functional of the form... 

Usually, self-consistent, all-electron calculations are performed within the relativistic local density approximation (LDA). The general gradient approximation (GGA), also in the relativistic form, RGGA, are then included perturbatively in E p,m). The accuracy depends on the adequate knowledge of the potential, whose exact form is, however, unknown. There is quite a number of these potentials and their choice is dependent on the system. Thus, PBE is usually favored by the physics community, PBEO, BLYP, B3LYP, B88/P86, etc., by the chemical community, while LDA is still used extensively for the solid state. 

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