  Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the {\alpha}-phase
(orthorhombic) are exciting quasi two-dimensional (2D) electronic systems
exhibiting a fascinating series of electronic ground states under different
conditions. Pristine TiNX are semiconductors with varying energy gaps and
possess attractive properties for potential applications in the fields of
optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated
TiNCl becomes superconducting at reasonably high temperature in the
{\alpha}-phase. We have revisited the electronic band structure of these
compounds using density functional theory (DFT) based first-principles
calculations. The atomic species and orbital resolved partial electronic energy
density of states are calculated together with the total density of states
(TDOS). The structural and elastic properties have been investigated in details
for these layered compounds for the first time. The elastic anisotropy has been
explored. The optical properties, including energy dependent real and imaginary
parts of the dielectric constant, optical conductivity, reflectivity, and loss
function of TiNX are studied for the first time. The Debye temperatures of
these compounds have been calculated and the related thermal and phonon
parameters are discussed. The calculated physical parameters are compared with
existing theoretical and experimental results and show fair agreement, where
available. All these compounds are found to reflect electromagnetic radiation
strongly in the mid ultraviolet region. The elastic properties show high degree
of anisotropy. The lattice is highly compressible along the crystallographic
c-direction. The effect of halogen atoms on various structural, elastic,
electronic, and thermal properties in TiNX are also discussed in detail.
