How do I pick a basis set for an ab-initio Hartree-Fock evaluation ? In other words, what are the important characteristics of a basis set so that a proper choice can be made ?

  • $\begingroup$ I wonder why you are using Hartree-Fock at all. DFT is more accurate at the same computational cost so Hartree-Fock is primarily used only as the starting point for many-body calculations such as coupled-cluster. $\endgroup$ – Jeff Apr 13 '13 at 20:35

This is a pretty big topic, but the basic important qualities of an atom-centered basis set are:

  • The number of separate, unlinked functions it uses at the valence level (the so-called *zeta* count), which allow the modeling of that many different electronic environments, practically speaking.
  • Additional higher angular momentum so-called *polarisation* functions to allow for more angular complexity.
  • Whether it has diffuse functions to model more spacially extensive orbitals - so called *augmented* functions.

Generally, though, for Hartree-Fock:

  • Double-zeta for very quick, very rough structural parameters.
  • Double-zeta + polarisation for slightly less rough structural information, large systems (100+ atoms), or simple bonding environments like alkanes.
  • Triple-zeta for better accuracy and useful energies.
  • Augmented functions if you're working with anions.

Going to a better basis set than this for Hartree-Fock probably won't gain you much. In any case, unless you're moving on to a more complex method, you should probably be using density-functional theory (DFT) instead.

For more information on basis sets including how different basis sets are labelled, I recommend chapter 5.2 in Jensen's "Introduction to Computational Chemistry".

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