Report an inconsistency in QMC measurement of stiffness - Comp-phys-alps-users

27 Sep 2015


      Dear all,
Recently I calculate hardcore on a two-leg ladder with nearest and next nearest neighbor hopping using QMC with direct loop update (dirloop_sse).
I can define the lattice in two different ways (see the followings). The problem is the stiffness since the two ways give differnet resutls. I find the result from way 2 is about double of the one from way 1.
This addresses a question that some measurement is related to the way how to define the lattice. It seems to me that the users should know more about the details of the codes.
Sincerely,
Huaiming Guo
way1 (see the following): the unitcell contain one site, but is viewed as two dimension. It is the standard file provided by alps software.
<UNITCELL name="nnn2d" dimension="2">
  <VERTEX/>
  <EDGE type="0"><SOURCE vertex="1" offset="0 0"/><TARGET vertex="1" offset="1 0"/></EDGE>
  <EDGE type="1"><SOURCE vertex="1" offset="0 0"/><TARGET vertex="1" offset="0 1"/></EDGE>
  <EDGE type="2"><SOURCE vertex="1" offset="0 0"/><TARGET vertex="1" offset="1 1"/></EDGE>
  <EDGE type="2"><SOURCE vertex="1" offset="0 0"/><TARGET vertex="1" offset="1 -1"/></EDGE>
</UNITCELL>
<LATTICEGRAPH name = "ladder" vt_name="LadderLattice">
  <FINITELATTICE>
    <LATTICE ref="square lattice"/>
    <PARAMETER name="W" default="2"/>
    <EXTENT dimension="1" size="L"/>
    <EXTENT dimension="2" size="W"/>
    <BOUNDARY dimension="1" type="periodic"/>
    <BOUNDARY dimension="2" type="open"/>
  </FINITELATTICE>
  <UNITCELL ref="nnn2d"/>
</LATTICEGRAPH>
way2: the unitcell contains two sites (the two sites on the rung which is vertical to the legs).
<UNITCELL name="nnn1d" dimension="1" vertices="2">
  <VERTEX type="0" />
  <VERTEX type="1" />
  <EDGE type="0"><SOURCE vertex="1" offset="0"/><TARGET vertex="1" offset="1"/></EDGE>
  <EDGE type="1"><SOURCE vertex="2" offset="0"/><TARGET vertex="2" offset="1"/></EDGE>
  <EDGE type="2"><SOURCE vertex="1" offset="0"/><TARGET vertex="2" offset="0"/></EDGE>
  <EDGE type="3"><SOURCE vertex="1" offset="0"/><TARGET vertex="2" offset="1"/></EDGE>
  <EDGE type="3"><SOURCE vertex="2" offset="0"/><TARGET vertex="1" offset="1"/></EDGE>
</UNITCELL>
<LATTICEGRAPH name = "chain lattice">
  <FINITELATTICE>
    <LATTICE ref="chain lattice"/>
    <EXTENT dimension="1" size ="L"/>
    <BOUNDARY type="periodic"/>
  </FINITELATTICE>
  <UNITCELL ref="nnn1d"/>
</LATTICEGRAPH>