
Variational Method Applied to the Harmonic Oscillator© 
S. Keith Dunn Centre College Danville, KY 40422 United States
mail to: dunnk@centre.edu


Abstract 
This laboratory exercise is a simple, onedimensional problem that introduces undergraduate physical chemistry students to the variational method. Students find approximate solutions to the Schrodinger equation for the quantum harmonic oscillator using the sinusoidal particleinabox wavefunctions as a basis set. The details of the variational method, including constructing trial wavefunctions from linear combinations of an orthonormal basis set, are explored without the mathematical complexities involved with even the simplest Molecular Orbital (MO) theory calculations. The onedimensional basis functions and trial wavefunctions are plotted on simple XY graphs, so that the important concept of additivity of basis functions is clearly demonstrated. Symmetry characteristics of the basis functions and the hamiltonian are used to discover why odd basis functions contribute to one set of trial wavefunctions, while even basis functions contribute to another. Additionally, since the harmonic oscillator wavefunctions are known, the students compare their trial wavefunctions and energies with actual ones. By comparison then, students can see the value and limitations of approximate methods of solving the Schrodinger equation. This exercise is an effective way to introduce students to the basics of MO theory before they are asked to use software packages like Spartan or Hyperchem to solve chemically relevant problems.


Commentary 

Keywords 

Audiences: 
UpperDivision Undergraduate 
Pedagogies: 
ComputerBased Learning 
Domains: 
Physical Chemistry 
Topics: 
MO Theory, Quantum Chemistry, Mathematics / Symbolic Mathematics 

Documents 

File Name  Description  Software Type  Software Version 
vari_harm2001.mcd 
Mathcad 2001 version 


vari_harm2001.pdf 
ReadOnly Document 
mathcad 
Mathcad 2001 
vari_harm8.mcd 
Mathcad 8 version. 
Mathcad 
8 

JCE Subscribers only: name and password or institutional IP number access required. 

Citations 


Comments to: S. Keith Dunn at dunnk@centre.edu


©Copyright 2002 Journal of Chemical Education

