The Effects of Intramolecular Basis Set Superposition Error on Conformational Energy Differences: 1,2-Difluoroethane and 1,2-Dimethoxyethane

Young-Kyu Han, Kyoung Hoon Kim, Sang-Kil Son, and Yoon Sup Lee

[BibTeX]

One of the possible errors in the evaluation of the energy differences between various conformers in a molecule is conformation dependent intramolecular basis set superposition error(BSSE). We have studied this BSSE for 1,2-difluoroethane(DFE) and 1,2-dimethoxyethane(DME) molecules. The BSSE is estimated using counterpoise(CP) method at the Møller-Plesset second order perturbation(MP2) level of theory with various basis sets. The fluorine-fluorine gauche, anti, and eclipse forms for DFE and nine conformers for DME are calculated. The BSSE effects on the energy difference between eclipse(a transition state) and gauche forms are 0.2–1.2 kcal/mol for the various basis sets. However, the BSSE effects on the energy differences between local minima, gauche and anti forms, are not so large (less than 0.2 kcal/mol). For the larger DME molecule, the errors can be up to 0.4 kcal/mol. Considering that the energy differences between conformers of DME are in the range of 0.2–3.0 kcal/mol, the estimated BSSEs are not negligible. The intramolecular BSSE can be a major huddle in the evaluation of the conformational energy difference even for the molecules of the moderate size such as DME.

Tags: BSSE, KAIST