Hi,
On Fri, Jun 18, 2010 at 4:07 AM, Vipin Varma varma@th.physik.uni-bonn.de wrote:
I'm trying to get the gap (between the Sz=0 sector and the Sz=1/2 i.e. spinon) for a spin-1/2 anti-ferromagnetic Hiesenberg chain for a finite system L=4. No eigenvalues are calculated in the output file when I perform sparse diagonalization on the below parameter file for getting the spinon eigenvalue:
MODEL="spin"; LATTICE="chain lattice"; LATTICE_LIBRARY="../lattices.xml" MODEL_LIBRARY="../models.xml" CONSERVED_QUANTUMNUMBERS="Sz"; local_S=1/2; J=1; {L=4; Sz_total=1/2;}
It seems only the sectors with Sz= {-1,0,+1} can be input to the Lanczos algorithm. Can somebody tell me what I am missing?
When you calculate Heisenberg model on L=4 chain lattice, there will only be 5 sectors available. up=4, down=0 -> Sz_total=2 up=3, down=1 -> Sz_total=1 up=2, down=2 -> Sz_total=0 up=1, down=3 -> Sz_total=-1 up=0, down=4 -> Sz_total=-2
Note that if you increase one up spin, one down spin must be decreased, so \Delta Sz_total is always an integer.