Kirschner, Karl N.Karl N.KirschnerHeiden, WolfgangWolfgangHeidenReith, DirkDirkReith2022-05-062022-05-062020https://publica.fraunhofer.de/handle/publica/41601010.1080/1539445X.2020.1714656In an effort to assist researchers in choosing basis sets for quantum mechanical modeling of molecules (i.e. balancing calculation cost versus desired accuracy), we present a systematic study on the accuracy of computed conformational relative energies and their geometries in comparison to MP2/CBS and MP2/AV5Z data, respectively. In order to do so, we introduce a new nomenclature to unambiguously indicate how a CBS extrapolation was computed. Nineteen minima and transition states of buta-1,3-diene, propan-2-ol and the water dimer were optimized using 45 different basis sets. Specifically, this includes one Pople (i.e. 6-31G(d)), 8 Dunning (i.e. VXZ and AVXZ, X = 2-5), 25 Jensen (i.e. pc-n, pcseg-n, aug-pcseg-n, pcSseg-n, and aug-pcSseg-n, n = 0-4), and 9 Karlsruhe (e.g. def2-SV(P), def2-QZVPPD) basis sets. The molecules were chosen to represent both common and electronically diverse molecular systems. In comparison to MP2/CBS relative energies computed using the largest Jensen basis sets (i.e. n = 2,3,4), the use of smaller sizes (n = 0,1,2 and n = 1,2,3) provides results that are within 0.11-0.24 and 0.09-0.16 kcal⋅mol −1. To practically guide researchers in their basis set choice, an equation is introduced that ranks basis sets based on a user-defined balance between their accuracy and calculation cost. Furthermore, we explain why the aug-pcseg-2, def2-TZVPPD and def2-TZVP basis sets are very suitable choices to balance speed and accuracy.en003500005006518journal article