  We introduce the first multiorbital effective tight-binding model to describe
the effect of electron-electron interactions in this system. Upon fixing all
the effective hopping parameters in the normal state against an ab initio band
structure, and with only the overall scale of the interactions as the sole
adjustable parameter, we find that a self-consistent Hartree-Fock solution
reproduces extremely well the experimental behavior of the charge density wave
(CDW) order parameter in the full range $0<T<T_{\text{c}}$, as well as the
precise reciprocal space locations of the partial gap opening and Fermi arc
development. The interaction strengths extracted from fitting to the
experimental CDW gap are consistent with those derived from an independent
Stoner-type analysis.
