Abstract: 

    Molecular orbital calculations were done using quantum mechanical predictions done by computer software. wxMacMolPlt was used to create the input files for the calculations.³  The calculations themselves were done using Gamess.⁴  The JMOL software was used to analyze the data.⁵  Geometry optimizations and energy calculations were done on three different molecules, and the results were compared between several sized basis sets.

Introduction: 

    Looking at the "electronic structure of a molecule" shows much about how it reacts.⁸  The electronic structure of molecules can be useful in finding out where the electrons might be, and can help in predicting properties like the dipole moment, vibrational frequency, and if the molecule will donate its electrons.⁸  Originally, quantum calculations were done by scientists slaving away on paper, but with computers, computations of geometry and energy predictions become much easier.⁸ Even with the large cost of hardware, the advantage of being able to calculate such large “basis set” wavefunctions overpowers the costs. When doing these calcluations, a larger basis set helps create a more accurate prediction of energy and molecular geometries. To do these geometry optimizations, the computer tries to find an “arrangement of atoms” that minimizes the energy of the system.⁸ The basis sets used in this experiment, in order of increasing size were, 6-21G, 6-31G, and DZV (double zeta valence).⁸ DFT, or density functional calculations, were used for the larger molecules because it is more efficient when it comes to the increased number of electrons.⁸ The molecules tested were dichlorine, hydrogen cyanide, and fluorobenzene. Each molecule's geometry optimization was found at each basis set and the molecules were then further examined with other calcluations. 

Clicking on the names below the pictures of each molecule will take you to pages with further details on that molecule.   

                              
                     Dichlorine                                           Hydrogen Cyanide                                Fluorobenzene

Conclusion:

    Quantum Calculations with computers can be useful when the materials for testing the compounds, or the molecules themselves cost a lot of money or produce a lot of waste. It is less costly, and more environmentally friendly to make predictions.The experiments can be complicated as well as costly, and doing calculations with computer programs just may actually be the easier route.  The computational calculations can be done on molecules that do not necessarily exist in the natural world as well.  This can allow chemists to explore new chemical theories or simply learn more about existing theories.