Ground states of the one-dimensional anisotropic extended Hubbard model

We investigate a one-dimensional half-filled electron system with on-site and spin-dependent nearest-neighbor-site Coulomb interactions. Non-Tomonaga-Luttinger-type scatterings bring about Gaussian and hidden SU(2) Berezinskii-Kosterlitz-Thouless transitions in the charge and spin parts. We accurately determine these critical points using the level-spectroscopy method. The boundaries deviate from those given by bosonization prediction with the increase of interactions. In particular, in the easy-plain anisotropy region, we find a crossing point of transition lines in the charge and spin parts, which is a multicritical point of four phases. We also check consistencies among excitation levels.