The molecular electrostatic potential is a one-electron property that can be obtained experimentally through X-ray diffraction studies. Much more commonly, the electrostatic potential is obtained computationally using either the Hartree-Fock (HF) method or Density Functional Theory (DFT). The quality of the electrostatic potential depends on the basis set used to compute the electron density. Here we investigate the dependence of the electrostatic potential on basis set size. This is done for three molecules with interesting (non-trivial) electrostatic potentials, HCN, BrCN, and H3C-CCH. We find that it is generally not advisable to use very small basis sets, such as STO-3G, to compute the electrostatic potential, and that 3-21G* is generally the smallest basis that can be reliably be used for this purpose. It is also discovered that density functional methods, when used along with small basis sets (even as large as 6-31+G*) tend to missassign a potential energy maximum located on the methyl carbon on methyl-acetylene. This is not the case for HF, which locates this maximum with even the smallest basis set.

How does the quality of the electrostatic potential depend on the size of the basis set used?

251st National Meeting (2016)

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