Molecular orbital (MO) theory is a method for writing
electronic wavefunctions of diatomic molecules where the distribution of a
single electron can be defined over the entire molecule.1 Using MO
allows for different properties of molecules to be predicted with very good
accuracy. The best approximations of wavefunctions occur when the variational
principle is applied. The principle states that the wavefunction with the
lowest energy is the best approximation for the actual wavefunction.2
The caveat with using this theory is that it can be done relatively easily
within the domain of a single atom with one electron; however, as more atoms
and more electrons are introduced, it becomes vastly more complicated.
Experimental
The experiment performed utilized a number of software
programs performing calculations needed to obtain the MO information for three
molecules. MO calculations were performed on Chlorobromide (ClBr), Nitrogen
Dioxide (NO2), and Phenylacetylene (C8H6). The
software programs used for calculations and web design were Avogradro,
MacMolPlt, GAMESS(Q), Igor, Jmol, and Seamonkey.
Avogadro was the software for drawing the molecules and
performing simple molecular calculations like bond length and bond angles. MacMolPlt
performed geometry optimization using MOPAC, which is a semi-empirical method
for calculating the geometries of molecules. The semi-empirical method allowed
for the use of a number of Hamiltonians to optimize the geometry, with AM1 and
PM3 being used throughout the initial calculations. The best level of MO theory
utilized was Ab initio where the
basis sets for the wavefunction calculations involve all integral calculations.3
The Ab initio basis sets used were:
3-21G, 6-31G, and DZV (double zeta valence). GAMESS was the software that ran
quantum mechanical calculations for all levels of theory and GAMESSQ allowed
for queuing up the necessary calculations for GAMESS to perform.
Igor was the statistical software used to plot potential
energy versus bond length for the diatomic molecule. Lastly, Jmol and Seamonkey
were used to create and edit the webpage.
Links to Molecules
References
1. Cooksy,
Andrew. Quantum Chemistry and Molecular
Interactions; Pearson: New Jersey, 2014; pp 214.
2. Gutow,
Jonathon. Molecular Orbital (MO)
Calculations; laboratory manual: University of Wisconsin-Oshkosh, revised
Feb 2015.
3. Gutow, Jonathon.
Molecular Orbital (MO) Calculations;
laboratory manual: University of Wisconsin-Oshkosh, revised Feb 2015.