On 25 Jul 2014, at 10:28, Stone, Matthew B. <
stonemb@ornl.gov> wrote:
> ALPS community,
>
> I am interested in calculating the states and the spin-spin correlation functions for a dimerized chain.
This type of structure is sometimes called an alternating chain. It consists of spins coupled along one-dimension with alternating strong and weak Heisenberg exchange parameters:
> J0---J1---J0---J1---J0---
>
> Using the tutorials and the ALPS website, I have assembled what I think are the correct UNITCELL and LATTICEGRAPH (see end of message).
>
>
The correct unit cell should be:
<UNITCELL name="anisotropic1d" dimension="1">
<VERTEX/>
<EDGE type="0">
<SOURCE
vertex="1" offset="0"/>
<TARGET vertex="2" offset="0"/>
</EDGE>
<EDGE type="1">
<SOURCE vertex="2" offset="0"/>
<TARGET vertex="1" offset="1"/>
</EDGE>
</UNITCELL>
Note that offsets refer to unit cells and vertex numbers to the two vertices inside the unit cell. I would also propose to call the unit cell "dimerized" and not "anisotropic1d"
> Q1: Is there a way to check this definition visually? The wiki suggests the command
> printgraph parameter_file
Yes
>
> Q2: does the predefined ‘MODEL’ “spin” account for J0 and J1 exchange?
Yes
>
> Q3: Can ‘S’ also be a conserved quantum number.
No, since only Sz conservation can be implemented in a straightforward manner
Best regards
Matthias Troyer
>
> Thanks for your assistance.
>
> Matt Stone
>
>
>
> parms = [{
> 'LATTICE' : "dimechain",
> 'LATTICE_LIBRARY' : "latticeCN.xml",
> 'MODEL' : "spin",
> 'local_S'
: 0.5,
> 'J0' : 1,
> 'J1' : 0.125,
> 'L' : 6,
> 'CONSERVED_QUANTUMNUMBERS' : 'Sz',
> 'MEASURE_CORRELATIONS[Diagonal spin correlations]=' : 'Sz',
> 'MEASURE_CORRELATIONS[Offdiagonal_spin_correlations1]' :
'Splus:Sminus',
> 'MEASURE_CORRELATIONS[Offdiagonal_spin_correlations2]' : ‘Sminus:Splus,
> 'D' : 0.0,
> 'h' : 0.0,
> }]
>
>
> <UNITCELL name="anisotropic1d" dimension="1">
> <VERTEX/>
> <EDGE type="0">
> <SOURCE vertex="1"
offset="0"/>
> <TARGET vertex="1" offset="0.5"/>
> </EDGE>
> <EDGE type="1">
> <SOURCE vertex="1" offset="0.5"/>
> <TARGET vertex="1" offset="1"/>
> </EDGE>
> </UNITCELL>
>
> <LATTICEGRAPH name = "dimechain" vt_name="dimechainLattice">
> <FINITELATTICE>
> <LATTICE ref="chain lattice"/>
> <EXTENT dimension="1" size="L"/>
> <BOUNDARY dimension="1" type="periodic"/>
> </FINITELATTICE>
> <UNITCELL ref="anisotropic1d"/>
> </LATTICEGRAPH>
>
> <!-- From the default lattices -->
> <LATTICE name="chain lattice" dimension="1">
> <PARAMETER name="a" default="1"/>
> <BASIS><VECTOR>a</VECTOR></BASIS>
> <RECIPROCALBASIS><VECTOR>2*pi/a</VECTOR></RECIPROCALBASIS>
> </LATTICE>
>