ADF and BAND use Slater-type orbitals (STOs), which have the correct nuclear cusp and long-range behavior, as opposed to Gaussian-type orbitals. BAND can also use numerical atomic orbitals. Properties like spin-state energies and reaction and activation energies are demonstrated to converge much quicker with STOs than with Gaussians with respect to basis set size. Furthermore, the correct asymptotic behavior of STOs close to the nucleus and at large distances is advantageous for spectroscopic properties such as NMR, EPR and UV/VIS.
All-electron basis sets for all elements
STO basis sets for the entire periodic table are included with the binaries of the ADF modeling suite, and can also be provided upon request. There are basis sets for non-relativistic calculations, and basis sets optimized for use with ZORA (available for download), the zeroth-order regular approximated relativistic Hamiltonian. The user usually should not worry about the location of the basis sets as it will automatically be handled when using the basis key.
For most applications, even for systems containing only light atoms, we recommend using ZORA as it is an excellent approximation to the fully relativistic Dirac equation, especially in the valence region, which is important in quantum chemical calculations. ADF has basis sets especially optimized for use with ZORA (E. van Lenthe and E.J. Baerends, Optimized Slater-type basis sets for the elements 1-118. J. Comp. Chem. 24, 1142 (2003)). The ZORA basis sets are available as DZ (double zeta), TZP (triple zeta with 1 polarization function), TZ2P (triple zeta with 2 polarization functions) and QZ4P (quadruple zeta with 4 polarization functions). Except for the QZ4P basis, basis sets are also available with a frozen core for most elements.
Specialized basis sets
There are also other basis sets such as the even-tempered basis sets by Del Chong and the NMR-optimized basis set (jcpl) by Jochen Autschbach included with the binaries.