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I am trying to calculate the energy of complex molecules with DFT and have a question about the Ahlrichs (Karlsruhe) def2 basis sets.

What is the difference between the def2-SV, def2-SV(P), and def2-SVP? Do they only differ in whether the basis set includes split valence polarization or not?

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    $\begingroup$ Welcome to Chemistry.SE! If you haven't already, please take a minute to look over the help center and tour page to better understand our guidelines and question policies. $\endgroup$ – A.K. Feb 13 '19 at 16:13
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    $\begingroup$ If you want quantifyable results, you should not use SVP basis sets. They have a very broad error distribution and are generally not really usable for accurate results. $\endgroup$ – Fl.pf. Mar 13 '19 at 14:56
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Def2-SVP has the polarisation functions on all atoms, -SV(P) does not have these functions on the hydrogen atoms and -SV does without them.

In future, you can check on the EMSL Basis Set Exchange - https://bse.pnl.gov/bse/portal - It wouldn't give you an answer explicitily, but you can view the basis set for different atoms and see how the different sets vary.

A side note - If your 'complex molecules' aren't too large, consider the larger Def2-TZVP basis set. Errors at the Def2-SVP level can be several kcal which may significantly impact your study. As an alternative, consider the PC-n family of basis sets from Frank Jensen. If the Def2-TZVP set is too large, the double-zeta PC-1 might work well.

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