### Abstract:

Density functional theory is a successful theory used in physics, chemistry and
nanoscience to describe the ground state properties of solids and molecules. It calculates
ground state energies and related properties by using the density of the valence
electrons as a fundamental variable. In a system of interacting electrons, the electrons
will correlate due to the Pauli exclusion principle, as well as their coulomb
repulsion. This interaction energy is known as the exchange-correlation energy and
is approximated in density functional theory because it is the only unknown in the
energy as a functional of density. The simplest model to approximate this exchangecorrelation
energy is the local density approximation, which only relies on the local
density of the valence electrons at every point. Generalized gradient approximations
are approximations which build upon the local density approximation by also using
the gradient of the local density. Recently, many new versions of the generalized gradient
approximation have been developed to attempt to obtain better energetic and
structural properties either at the same time, or at the expense of the other. In this
study, we examine the performance of these models by calculating the atomization
energy of the AE6 test set. The cohesive energy, lattice constant and bulk modulus of
a four solid test set was also calculated. These calculations were done using ABINIT,
a density functional theory code that uses a pseudopotential model with plane waves
to examine molecules and solids. One of the more recently developed generalized
gradient approximation models, the SOGGA, is tested to compare with the standard
models. The accuracy of using a pseudopotential model is also tested. It was found
that by using a generalized gradient approximation that was better for energy calculations,
the structural property calculations would not be as accurate. The SOGGA
is a functional that approximates structural properties of solids accurately but does
not calculate energies as well. It was also found that using a pseudopotential model
resulted in a 1% difference from the all electron calculations.