Hi everyone,
I'm reading DMRG tutorials in
http://alps.comp-phys.org/mediawiki/index.php/ALPS_2_Tutorials:DMRG-01_DMRG.
and
http://alps.comp-phys.org/mediawiki/index.php/ALPS_2_Tutorials:DMRG-02_Gaps
It suggested me to extrapolate energies and energy gaps to D(maxstates) -> infinity.
The question is about nonlinear extrapolation. In the case spin 1/2 gap versus 1/L, there is a linear relation and I can easily polyfit it linearly and get the gap in L->Inf limit.
But in the case of quantities such as gaps versus D(maxstates), there is no simple linear relation.
For example:
Each time I enlarge D by 50, energy gaps change by the following values:
[ -2.49851713e-08, -1.45270462e-11, -2.84217094e-14,
-5.50670620e-14]
which slows down changing by smaller and smaller values.
I have done some exponential curve fittings in matlab but it become confusing when you have many models to fit it.
How can I extrapolate such a nonlinear curve to D->Inf limit? Is there any standard way to do this?
LiuBiao
ll070616(a)126.com
Hi everyone,
I'm reading DMRG tutorials in
http://alps.comp-phys.org/mediawiki/index.php/ALPS_2_Tutorials:DMRG-01_DMRG.
When treating spin 1 Heisenberg chain with open boundary conditions, 2 spin 1/2 sites were added to both ends of the spin 1 chain. Why?
I have completely no idea about this special treatment. Can anyone give further explanations?
LiuBiao
ll070616(a)126.com
Dear All,
We are trying to reproduce results from this paper using the dirloop_sse
code.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.89.047202
Typically we setup the simulation such that it calculates the spin-spin
correlations and then calculate the staggered susceptibility from that.
The results for uniform susceptibility obtained that way seem to
reproduce well the known results, however it is not the case of the
staggered susceptibility.
In particular the staggered susceptibility seems to be the same for even
and odd chain lengths and to scale in a bizarre way with length. This
happens even for very short chains where we would expect the difference
between odd/even to be significant.
Is this a known problem with a simple explanation?
Regards,
Stanislaw and Kirill