Examination of Gaussian-Type Basis Sets on Alkali Metal Iodides

Abstract

In theoretical studies using ab initio or density functional theory (DFT) methods, adequate choices of a theoretical method and a basis set are very important in obtaining reliable results. Unfortunately, basis sets, especially for elements beyond the 4 row in the periodic table, are relatively limited, although various accurate theoretical methods such as MPn, QCISD and B3LYP etc. have been currently developed. Theoretical studies on compounds containing iodine, the 4 row halogen atom, are less abundant compared to those containing F, Cl or Br. However, compounds containing iodine atom play important roles in many chemical reactions. Currently, three kinds of basis sets on iodine (STO-3G, 321G and Midi! basis sets) without using effective core potential (ECP) have been implemented in most of quantum mechanical programs. However any results obtained from theoretical works using these basis sets or the ECP basis sets might not be so accurate for reactions containing iodine atom, because these basis sets are relatively low-grade in quality. Especially, an iodide ion is considered as an intermediate or a product in many reactions, but none of these basis sets have incorporated a diffuse function. Therefore, any theoretical results obtained by using these basis sets could not be accurate due to incorrect nature of iodide anions. On the other hand, Andzeml et al. have reported the contracted Gaussian basis sets for halogen elements. These basis sets have similar quality to the basis sets generated earlier by Huzinaga et al. but Andzeml et al. have argued that their basis sets after splitting of valance orbitals and augmented with polarization function, have given better atomic total energies and properties of atomic valence orbitals. Recently, Wiberg et al. have also reported works for organometallic compounds containing iodine. In the work, they have used a TZ-quality basis set with two D polarization functions and one SP diffuse function for iodine. Therefore, in order to obtain reliable results on the reactions containing iodide anion, various types of basis set are re-examined in this work.