By Iaroslavna Kovalenko and Jillian Pabalan

Faculty Mentor: Leanna Giancarlo

Abstract

The applicability and limitations of the GAMESS dihydrogen potential energy curve computational tool were evaluated for the following diatomic molecules: H2, N2, F2, Cl2, and Br2. The aug-cc-pVDZ basis set and the B3LYP density functional theory (DFT) functional were employed to ensure more accurate electronic energy results for each calculation. Potential energy curves were generated for each molecule by plotting the electronic energy as a function of interatomic distance, and the bond dissociation energies (BDEs) and radii of diatomic molecules were determined. The radii were determined to be 76 pm for H2, 110. pm for N2, 140. pm for F2, 200. pm for Cl2, and 230. pm for Br2, with percent errors of 3%, 0%, -2%, 0.5%, and 0.9%, respectively. These results show that this computational tool can determine interatomic distances in diatomic molecules with high accuracy because the molecules are in the most stable form near the minimum of the potential energy curve, where calculations are most accurate. The determined BDEs were 699 kJ/mol for H2, 1759 kJ/mol for N2, 415 kJ/mol for F2, 418 kJ/mol for Cl2, and 349 kJ/mol for Br2, with percent errors of 60.3%, 85.9%, 159%, 72.3%, and 83.7%, respectively. The high percent error in the BDE is due to the complex electronic structure of the unstable radical species upon bond dissociation, leading to larger discrepancies in calculations. Thus, computational tools should be used mindfully, and the specific basis set and DFT functional should be selected depending on the nature of each system. While computational tools can reasonably estimate bond lengths in homonuclear diatomic molecules, accurate BDEs require more advanced methods of determination.