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Phase diagrams of the one-dimensional extended Hubbard model (includingnearest-neighbor interaction $V$) at half- and quarter-filling are studied byobserving level crossings of excitation spectra using the exactdiagonalization. This method is based on the Tomonaga-Luttinger liquid theoryincluding logarithmic corrections which stem from the renormalization of theUmklapp- and the backward-scattering effects.  Using this approach, the phase boundaries are determined with high accuracy,and then the structure of the phase diagram is clarified. At half-filling, thephase diagram consists of two  Berezinskii-Kosterlitz-Thouless (BKT) transition lines and one Gaussiantransition line in the charge sector, and one spin-gap transition line.  This structure reflects the U(1) $\otimes$ SU(2) symmetry of the electronsystem. Near the $U=2V$ line, the Gaussian and the spin-gap transitions takeplace independently from the weak- to the intermediate-coupling region, butthese two transition lines are coupled in the strong-coupling region. Thisresult demonstrates existence of a tricritical point and abond-charge-density-wave (BCDW) phase between charge- and spin-density-wave(CDW, SDW) phases. To clarify this mechanism of the transition, we alsoinvestigate effect of a correlated hopping term which plays a role to enlargeBCDW and bond-spin-density-wave (BSDW) phases. At quarter-filling, a similarcrossover phenomenon also takes place in the large-$V$ region involvingspin-gap and BKT-type metal-insulator transitions.Comment: 18 pages(REVTeX), 17 figures(EPS(color)), 3 tables, Detailed paper of  JPSJ 68 (1999) 3123 (cond-mat/9903227), see also cond-mat/000341

Tricritical behavior in the extended Hubbard chains