Search for "extended Hückel method" in Full Text gives 2 result(s) in Beilstein Journal of Nanotechnology.
Beilstein J. Nanotechnol. 2022, 13, 721–729, doi:10.3762/bjnano.13.64
Beilstein J. Nanotechnol. 2016, 7, 418–431, doi:10.3762/bjnano.7.37