Abstract.
Geometries of free 1H-indole-3-acetic acid (IAA) and IAA hydrogen bond dimer were optimized at several computational levels: molecular mechanics, semiempirical methods, ab initio density functional theory with SVWN (Slater-Vosko-Wilk-Nusair) and Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP) functionals, and Hartree-Fock (HF). Bond length matrices X(mxn) (m = number of bonds, n = number of experimental determinations and theoretical calculations) and their transposes X(nxm) for IAA monomer, IAA dimer, and hydrogen bond ring (angles included) were analyzed using principal component analysis (PCA) and hierarchical cluster analysis (HCA). Ab initio methods prove to be superior to molecular mechanics and semiempirical methods: SVWN methods are the best for monomer, and B3LYP are best for dimer geometry optimization. The B3LYP and HF methods can be used equally well for optimization of the dimer ring geometry. Other hydrogen bond and aromaticity structural parameters exhibit preference either for B3LYP or SVWN methods.

Keywords.
Carboxylic Acid; Chemometrics; Computational Methods; Cyclic Dimer; (Hetero)Aromaticity; Indole-3-Acetic Acid.

Keywords Plus.