Molecular Orbital Calculations
By: Mike Hainstock & Calli Rieder

Abstract:
        Molecular orbital calculations were done for HF, NFH2, and anisole using three different softwares including Jmol, WxMacMolPlt, and GAMESS.  Three levels of an initio theory were uses to calculate many properties for each molecule including geometry optimizations, molecular orbital diagrams, molecular electrostatic potential displays, partial atomic charge displays, dipole moments, and vibrational frequencies.  The DZV level of theory usually calculated the most accurate value in comparison to the experimental values.

Introduction:
        The electronic structure of a molecule is very important in determining many of its properties.  The molecular orbitals are represented by wavefunctions for the electrons.  Eigenfunctions and eigenvalues can only be solved for atoms with one electron, so approximations have to be made for molecules with many electrons.  The approximation is done by a linear combination of wavefunctions to represent the actual wavefunction as best as possible with c being the coefficient to each wavefunction ѱ.  The lowest energy prediction is calculated for the normalized set of wavefunctions.  The calculation done with the largest basis set will give the most accurate prediction.

        In this study, the diatomic molecule HF, the polyatomic NFH2, and the aromatic anisole will be looked at. Molecular Mechanics will be used to make initial molecular structures, and then ab initio levels of theory will then be used to analyze these three molecules.  Each molecule will be studied using three levels of theory of different basis set sizes.  In order of increasing basis set size, the theories are 621-G, 631-G, and double zeta valence (DZV).  The properties of these molecules that will be calculated include geometry optimizations, molecular orbital diagrams, molecular electrostatic potential displays, partial atomic charge displays, dipole moments, and vibrational frequencies.


       
HF Calculations                                         NFH2 Calculations                                                 Anisole Calculations

Vibrational Calculations for HF, NFH2, and Anisole

Conclusion:
        Through the computational study of HF, NFH2, and anisole, it was concluded that accurate results of various properties of the molecules can be calculated.  The DZV ab initio level of theory usually calculated the best results due to it having the largest basis set size compared to the other levels of theory.  Computation chemistry can come in very useful when it is too difficult or expensive to study certain molecules in the lab.  It can also be used to study the molecule’s properties before a laboratory study is conducted.  However, computation chemistry can become very time consuming and requires a great deal of computer space to be done successfully.

References:
1 Gutow, J. Molecular Orbital (MO) Calculations 2013, https://cms.gutow.uwosh.edu/Gutow/physical-chemistry-2/student-password-protected/lab-handouts/lab-handout-files/MO%20Calcs.pdf

Software used in this study:
    -       WxMacMolPlt
    -       GAMESS
    -       Jmol