Abstract
The optimized geometry, HOMO, LUMO, electrostatic
potential, and partial atomic charges were calculated for chlorine,
carbon disulfide, and nitrobenzene at different levels of molecular
theory. The different levels of molecular theory were 6-21G, 6-31G, DZV,
AM1, and PM3. DZV was the level of theory that was found to be most
effective at performing the calculations.
Introduction
Knowing the electronic structure of a molecule is
important because it allows one to understand the reactivity of the
molecule. There are many molecular properties that can be predicted
about the molecule if the electronic structure is understood. Some of
these properties are dipole moments, polarizability, vibrational
frequencies, probability of absorption of light and the tendency of the
molecule to donate electrons during a reaction. In the past electronic
structure calculations had to be done with a pen and paper but thanks to
the processing ability of modern computers the calculations can now be
done with computer programs.
In this experiment, the electronic structure of three
different molecules was calculated using three different computer
programs. The program called Avogadro was used to build the initial
structure of the molecules. This program allows the user to build a
molecule by drawing in the atoms and bonds of the molecule. Once the
molecule has been constructed the program can then calculate the
optimized geometry of the molecule. Once a molecule was constructed in
Avogadro the file could then be opened in the program MacMolPlt. The
MacMolPlt program takes a geometry optimized molecule and builds a file
for the molecule that selects the different types of calculations that
will be run on the molecule. Some of the different calculations include
vibrational frequency calculations, adding diffuse functions to improve
dipole moments, potential energy and bond length, and UV-Vis transition
energy calculations. Once a file was created in MacMolPlt it could be
opened in the GAMESS program. The GAMESS program performs the
calculations that were selected in the input file that was created in
MacMolPlt. The program runs the input file and creates a .log file that
contains the calculated results of the electronic structure
calculations.
The three molecules that were analyzed in this
experiment were chlorine, carbon disulfide, and nitrobenzene. The
calculations that were performed on all three molecules were geometry
optimization, highest occupied molecular orbital, lowest unoccupied
molecular orbital, electrostatic potential, partial atomic charges, and
dipole moment. In addition to these calculations the vibrational
frequency was calculated for chlorine, the dipole moments at each level
of theory were calculated for nitrobenzene, and UV-Vis transition energy
was calculated for nitrobenzene.
The following links show the calculated values for each molecule:
chlorine
carbon disulfide
nitrobenzene