  The 2D Hubbard model having the 2nd- and 3rd-neighbor transfer energies t'
and t" is investigated by use of the variational Monte Carlo method. At the
nearly optimal doping with on-site Coulomb energy U=6 (energy unit is t) the
condensation energy Econd for the d-wave superconductivity (SC) is computed for
lattices of sizes from 10x10 to 28x28 with the aim to get its bulk-limit value.
t" is fixed at -t'/2. Outside and in the neighborhood of the SDW region of
-0.16=<t'=<-0.08 the SC Econd dominates over the SDW Econd. At t'=-0.05 and
-0.10 we obtained a definitely finite bulk-limit SC Econd of the order of the
experimental value for YBCO. At t'=0 Econd nearly vanishes. For t'=<-0.18, the
SC Econd strongly oscillates as a function of the lattice size, when periodic
boundary conditions (b.c.'s) are imposed to both axes. In the case of periodic
and antiperiodic b.c.'s, a finite bulk-limit value is obtained at t'=-0.22.
Econd tends to vanish with further decrease of t'. With our results the SC of
LSCO is understandable with t'~ -0.10. The t' values of Hg1201, Tl2201 and
Na-CCOC seem close to -0.20 so that they locate in the boundary zone of SC
indicated in the present work. Slightly larger U improves the situation by
increasing Econd.
