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.
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.
