Pseudopotentials for non-local-density functionals

Ab initio pseudopotentials for the IIA and IIB elements have been generated in the framework of density-functional theory, including gradient corrections to the local-density approximation (LDA). Their accuracy and transferability have been tested by extensive atomic computations. We applied these pseudopotentials to the evaluation of bonding properties of homonuclear dimers. Our molecular computations, not restricted to light elements, allow a wide assessment of the importance of gradient corrections in finite systems. For all the dimers considered here, the LDA error for bond energies is reduced by roughly 50%. The relative improvement on equilibrium distances and vibrational frequencies is less impressive, but still important and systematic. We discuss the computational cost for the evaluation of gradient corrections in computer programs based on the plane-wave (or plane-wave-like) basis-set expansion.