Hi, Vipin,
On Sat, Jun 19, 2010 at 12:22 AM, Vipin Varma varma@th.physik.uni-bonn.de wrote:
For spin-1/2 systems, I tried lattices from L=4,6,...22 and got a gap of 0.025 after extrapolation (between Sz=0 and Sz=1); can I consider this good enough to call it gapless, or do I need bigger lattices?
If you need longer chain, you may consider using DMRG or QMC[1]. You can also find these applications in ALPS.
For spin-2, I tried lattices from L=4,6,8,10, and got a gap of 0.089; I guess the non-linear sigma model predicts S=2 system to have a gap of 0.071. Beyond L=12, it takes really long; what system size is considered "reasonable" for evalauting gap of spin-2?
According to [1], spin 2 system have spin-spin correlation length of order L=50. I don't think L=12 is sufficient to evaluate the gap.
[1] S. Todo and K. Kato, Phys. Rev. Lett. 87, 047203 (2001).
See more papers available at http://alps.comp-phys.org/mediawiki/index.php/PapersTalks
Best regards,