ADF combines a set of unique features that ensure reliable, accurate and efficient calculations.
ADF uses Slater-Type Orbitals (STO's) as basis functions. Slater basis functions resemble the true atomic orbitals more closely than Gaussian basis functions. Slaters can display the correct nuclear cusp and asymptotic decay. This leads to a more accurate and more intuitive description of the molecular orbitals at the same size of basis set. For a practical example of the benefits of STO's compared to Gaussians, see the STO vs GTO paper. A reason that most other programs use Gaussians to approximate Slaters is that Gaussian functions may be integrated analytically, while Slaters really must be integrated numerically. For this purpose ADF has a unique numerical integration method.
ADF uses the unique Te Velde - Baerends numerical integration scheme, in which the grid is automatically adapted to the available basis functions and to the number of significant digits demanded by the user through a single input parameter. It is straightforward to do very accurate integrations with far fewer points than in less highly developed schemes. For some more details see also numerical integration details.
ADF User Documentation: basis sets for ADF and BAND,
basis functions and orbitals,
numerical integration
ADF-GUI: accuracy and efficiency
Related:
frozen-core approximation,
numerical integration details,
ZORA,
ZORA STO basis sets that can be downloaded freely
