On the Search of a Modified STO‐3G Basis Set Optimized for Molecules

Atomic basis sets play a central role in molecular chemistry and computational studies. While numerous large and specialized basis sets have been developed, the minimal STO‐3G basis set continues to be used. It is commonly employed in the testing phase of calculations, for determining magnetic properties of larger systems, and for describing chemical environments in multilayer QM/QM' calculations focused on extended biological or material systems. The original STO‐3G basis set was optimized to fit a single atomic Slater‐type orbital, with no emphasis on energy or properties. In this study, we explore the possibilities, advantages, and drawbacks of re‐optimizing the STO‐3G basis set in the following ways: (i) targeting the total energy of different organic molecules rather than atoms during the optimization process; (ii) introducing different basis set “atom types” for the same atom, inspired by force fields; (iii) optimizing the basis set to improve equilibrium geometries and/or electric properties.