parameter t' does not seem to work - Comp-phys-alps-users

19 Oct 2018


      Dear all,
I was trying to run a simulation on the one-dimensional Bose-Hubbarad with
alternating tunneling rates t1 and t2, which is the bosonic analogue of the
Su-Schrieffer-Heeger(SSH) model. The lattice with one unit cell is made of
A and B sites. So there are two types of edges defined in the unicell:
-------------------------------
<UNITCELL name="sublattice1d" dimension="1">
  <VERTEX type="0"/>
  <VERTEX type="1"/>
  <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>
-------------------------------
Then I run a DMRG calculation. But I found that the results are the same as
when I used the "open chain lattice" with a single tunneling rates t. The
parameter t' does not seem to work. I think it should be something wrong
with my Model XML File. I have read one posting said that the number of
types of bond operators should be equal to the number of types of edges
defined in the unitcell. Is there anything wrong with my Model XML File? Is
my bond operator wrong?
My Model XML File is: -------------------------------
<MODELS>
<SITEBASIS name="boson">
  <PARAMETER name="Nmax" default="infinity"/>
  <QUANTUMNUMBER name="N" min="0" max="Nmax"/>
  <OPERATOR name="bdag" matrixelement="sqrt(N+1)">
    <CHANGE quantumnumber="N" change="1"/>
  </OPERATOR>
  <OPERATOR name="b" matrixelement="sqrt(N)">
    <CHANGE quantumnumber="N" change="-1"/>
  </OPERATOR>
  <OPERATOR name="n" matrixelement="N"/>
</SITEBASIS>
<BASIS name="boson">
  <SITEBASIS ref="boson"/>
  <CONSTRAINT quantumnumber="N" value="N_total"/>
</BASIS>
<SITEOPERATOR name="double_occupancy" site="x">
  n(x)*(n(x)-1)/2
</SITEOPERATOR>
<BONDOPERATOR name="boson_hop" source="x" target="y">
  bdag(x)*b(y)+bdag(y)*b(x)
</BONDOPERATOR>
<HAMILTONIAN name="boson Hubbard">
  <PARAMETER name="mu" default="0"/>
  <PARAMETER name="t" default="1"/>
  <PARAMETER name="t'" default="1"/>
  <PARAMETER name="U" default="0"/>
  <PARAMETER name="V" default="0"/>
  <BASIS ref="boson"/>
  <SITETERM site="i">
    <PARAMETER name="mu#" default="mu"/>
    <PARAMETER name="U#" default="U"/>
    -mu#*n(i)+U#*n(i)*(n(i)-1)/2
  </SITETERM>
   <BONDTERM type="0" source="i" target="j">
     -t*boson_hop(i,j)
   </BONDTERM>
   <BONDTERM type="1" source="i" target="j">
     -t'*boson_hop(i,j)
   </BONDTERM>
</HAMILTONIAN>
</MODELS>
-------------------------------
What should I do to solve the problem that parameter t' does not seem to
work?
Thanks,
Yulian Chen