Quantum scar is atypical and behaves exceptionally as for the ETH (eigenstate thermalization hypothesis) although the system itself is non-integrable. We have constructed various such quantum scars based on the orthogonal compact localized states of the flat band system which is described by the molecular orbital construction scheme we are also proposing recently. Have a look at “Flat band quantum scar” by Yoshihito Kuno, Tomonari Mizoguchi and Yasuhiro Hatsugai, published in Phys. Rev. B 102, 241115(R) (Dec.23, 2020). See also arXiv:2010.02044.