  We present an implementation of localized atomic orbital basis sets in the
projector augmented wave (PAW) formalism within the density functional theory
(DFT). The implementation in the real-space GPAW code provides a complementary
basis set to the accurate but computationally more demanding grid
representation. The possibility to switch seamlessly between the two
representations implies that simulations employing the local basis can be fine
tuned at the end of the calculation by switching to the grid, thereby combining
the strength of the two representations for optimal performance. The
implementation is tested by calculating atomization energies and equilibrium
bulk properties of a variety of molecules and solids, comparing to the grid
results. Finally, it is demonstrated how a grid-quality structure optimization
can be performed with significantly reduced computational effort by switching
between the grid and basis representations.
