About Basis Sets

Some explanations what selected Basis Sets mean

Basis set (Wikipedia):

“A basis set in theoretical and computational chemistry is a set of functions (called basis functions) which are combined in linear combinations (generally as part of a quantum chemical calculation) to create molecular orbitals. For convenience these functions are typically atomic orbitals centered on atoms, but can theoretically be any function; plane waves are frequently used in materials calculations.”

This overview sets the relation of what a basis set does and the calculation speed. Fastest for SCF [3] geometric optimization for C2H6 optimization with 2,4 sec was 3-21gsp, slowest with 11,4 h was d-aug-cc-pv5z (see Benchmark NWchem CH4 and C2H6).

 

  • STO-3Gfast – slater type orbitals – 3 gaussian [2]
  • 3-21G(*)  –  fast  (2,4 sec) – Split valence: two sets of functions in the valence region provide a more accurate representation of orbitals. The basis is used for very large molecules for which 6-31G(d) is too expensive [4].
  • 6-31g* – A significant improvement on 3-21G(*), 6-31G* adds polarization to all (non-hydrogen) atoms, and improves the modeling of core electrons. 6-31G* is often considered the best compromise of speed and accuracy, and is the most commonly used basis set. Available for elements H – Kr [2].
  • lanl2dz_ecp  lanl2dzdp_ecp
  • aug-cc-pvdz-dk
  • aug-pcs-3
  • roos_augmented_triple_zeta_ano

Links explaining Basis Sets

[1] Wavefun: Basis Set FAQ

[2] Wikipedia: Slater-type orbital

[3] Encyclopedia: Self-Consistent Field

[4]  http://www.tau.ac.il/~ephraim/Appendix_1.pdf

[5]  http://www.gaussian.com/g_tech/g_ur/m_basis_sets.htm

About ralf

I studied Geology at University Erlangen and got my PhD (bio-nanotechnology) at TU Dresden. In my spare time i program simulations and tinker around with data prediction methods. Frisbee is my favorite sport and i play guitar when my friends and i meet to make some music.
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