The formation of a charge density wave (CDW) in 2D materials caused by Peierls instability is a controversial topic. This study investigates the extensively debated role of Fermi surface nesting in causing the CDW state in 2H-NbSe2 materials. Four NbSe2 structures are identified on the basis of the characteristics in scanning tunneling microscopy images and first-principles simulations. The calculations reveal that an energetically favored filled phase corresponds to Peierls’ description with fully opened gaps at the CDW Brillouin zone boundary, resulting in a drop at the Fermi level in the density of states and scanning tunneling spectroscopy spectra. The electronic susceptibility and phonon instability indicate that the Fermi surface nesting is triggered by two nesting vectors, whereas the involvement of only one nesting vector leads to a so-called stripe phase. This comprehensive study demonstrates that the filled phase of NbSe2 can be categorized as a Peierls instability-induced CDW in two-dimensional systems.
