  Semi-empirical models of the solar atmosphere are used to study the radiative
environment of any planet in our solar system. There is a need for reliable
atomic data for neutral atoms and ions in the atmosphere to obtain improved
calculated spectra. Atomic parameters are crucial to computing the correct
population of elements through the whole stellar atmosphere. Although there is
a very good agreement between the observed and calculated spectra for the Sun,
there is still a mismatch in several spectral ranges due to the lack of atomic
data and its inaccuracies, particularly for neutrals like Mg I.
  To correctly represent many spectral lines of Mg I from the near-UV to the
mid-IR is necessary to add and update the atomic data involved in the atomic
processes that drive their formation. The improvements to the Mg I atomic model
are as follows: i) 127 strong lines, including their broadening data, were
added. ii) To obtain these lines, we increased from 26 to 85 the number of
energy levels. iii) Photoionization cross-section parameters were added and
updated. iv) Effective Collision Strengths (ECS) parameters were updated for
the first 25 levels using the existing data from the convergent close-coupling
(CCC) calculations. One of the most significant changes in our model is given
by the new ECS parameters for transitions involving levels between 26 and 54,
which were computed with a multi-configuration Breit-Pauli distorted-wave (DW)
method.
  More than one hundred transitions were added to our calculations, increasing
our capability of reproducing important features observed in the solar spectra.
We found a remarkable improvement in matching the solar spectra for wavelengths
higher than 3 um when our new DW ECS data was used in the model.
