Functional Group Basis Sets.

Abstract

The electronic properties of molecular functional groups (methyl, benzyl, etc.) are generally conserved across different molecules. However, atomic basis sets use the same electronic variational space on an element regardless of the functional group it is in. The computational expense of ab initio calculations on molecules may be reduced by constructing functional-group-specific basis sets. Our functional group (FG) basis functions are contractions over a "parent" atomic basis on all atoms in the functional group of interest. Contraction coefficients are obtained by calculating the functional group's electron density in a set of representative molecules and performing principle component analysis of the results. When the functional group's chemical identity is maintained (e.g. no bonds are broken in the group), FG basis sets provide accuracies similar to the parent basis while using a smaller number of basis functions. We demonstrate our methods by parametrizing FG basis sets for the -OH and -CH- functional groups and testing them in DFT calculations on several molecules. The results suggest that FG basis sets may be useful in many contexts, especially for treating spectator groups in mixed basis calculations.