Slater-type basis sets

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 Gaussian, see the STO vs GTO paper.

f(r) = Y_lmrⁿe^-ζr

The center of the function is at a nucleus, the Y_lm are spherical harmonics, and the exponential factor ζ (zeta) determines the long-range decay of the function. These STOs resemble the true atomic orbitals more closely than the more common Gaussian-Type Orbitals (GTO's). Therefore, fewer STO's than GTO's are needed for a given level of accuracy.

ADF has a database, which is included in the distribution, with thoroughly tested basis set files, ranging in quality from single-zeta to quadruple-zeta basis sets with various diffuse and polarization functions. All-electron and frozen-core basis sets are available for all elements, including lanthanides and actinides. The frozen-core approximation can be used to considerably reduce the computation time for systems with heavy nuclei, in a controlled manner. In the BAND program numerical orbitals are used in addition to STO's.

• STO's display the correct nuclear cusp and asymptotic decay
• basis sets for all elements (Z = 1 to 118)
  • all electron, frozen-core
  • SZ, DZ, DZP, TZP, TZ2P, QZ4P, even-tempered, diffuse
  • non-relativistic and ZORA relativistically optimized

Links

ADF User Documentation: basis sets for ADF and BAND, basis functions and orbitals
ADF-GUI: accuracy and efficiency
Related: ZORA STO basis sets that can be downloaded freely, frozen-core approximation, ZORA