Exploring the Nature of the H2 Bond. 1. Using Spreadsheet Calculations To Examine the Valence Bond and Molecular Orbital Methods

A three-part project for students in physical chemistry, computational chemistry, or independent study is described in which they explore applications of valence bond (VB) and molecular orbital–configuration interaction (MO–CI) treatments of H2. Using a scientific spreadsheet, students construct potential-energy (PE) curves for several states of H2 from the kinetic and potential energies, calculated from closed-form analytical expressions of the ten unique integrals arising from the Born–Oppenheimer Hamiltonian. For this project students use hydrogen 1s basis functions that include a screening parameter. From the calculated PE curves, they find the dissociation energy, De, and equilibrium internuclear distance, Re. In part I students use the Heitler–London (VB) form of the wave function to obtain the PE curves. In part II they optimize the value of the screening parameter to improve the results, and in part III they explore the treatment of H2, using both the simple MO wave function and the application of CI, with and without screening parameter optimization, to obtain the PE curves. Students compare their De and Re results with the experimental values. A set of questions, exercises, and a sample spreadsheet are provided as Supporting Information.