MEASURE_AVERAGE[Sz]=Sz;

it will measure the total Sz, not the Sz at each site.

Am I wrong about it?

Best,

Jun

On Wed, Jun 23, 2010 at 10:36 PM, Matthias Troyer <troyer@phys.ethz.ch> wrote:

It is better to use MEASURE_AVERAGE instead of MEASURE_LOCAL. That way you keep the translation symmetry and the reduction it brings in Hilbert space dimension.

Matthias

On 23 Jun 2010, at 16:43, jun wen wrote:

> Hello Matthias,
>
> Thanks for your message. You are right! I found that once I use the
> graph(where translation symmetry is absent) instead of lattice graph
> (where translation symmetry is present) to construct the lattice, then
> the local quantities can be computed via ED.
>
>
> Best regards,
> Jun

>
>
>
> On Wed, Jun 23, 2010 at 6:55 PM, Matthias Troyer <troyer@phys.ethz.ch> wrote:
>> The reason is probably that your lattice is translation invariant - then only average quantities and not local ones are computed, since all local quantities would be the same.
>>
>> Matthias
>>
>>
>> On 21 Jun 2010, at 08:33, jun wen wrote:
>>
>>> Hello All,
>>>
>>> I was trying to compute the local <S> in the Kitaev model defined on
>>> the honeycomb lattice with Exact Diagnolization
>>> Here is my parameter file:
>>>
>>> MODEL="kitaev";
>>> LATTICE="honeycomb lattice";
>>>
>>> LATTICE_LIBRARY="../../../definitions/kitaev/lattices.xml";
>>> MODEL_LIBRARY="../../../definitions/kitaev/models.xml";
>>>
>>> MEASURE_LOCAL[Local Sz]=Sz;
>>> MEASURE_LOCAL[Local Sx]=Sx;
>>> MEASURE_LOCAL[Local Sy]=Sy;
>>>
>>> local_S=1/2;
>>> L=2;
>>> W=2;
>>> J=1;
>>>
>>> However, in the output xml file, there are no such terms as the Local
>>> Sz or Local Splux or Local Sminus.
>>> I wonder if anyone could kindly point out what is the problem. The
>>> Kitaev model is defined in the following models.xml
>>> Thanks a lot!
>>>
>>> <MODELS>
>>> <SITEBASIS name="spin">
>>> <PARAMETER name="local_spin" default="local_S"/>
>>> <PARAMETER name="local_S" default="1/2"/>
>>> <QUANTUMNUMBER name="S" min="local_spin" max="local_spin"/>
>>> <QUANTUMNUMBER name="Sz" min="-S" max="S"/>
>>> <OPERATOR name="Splus" matrixelement="sqrt(S*(S+1)-Sz*(Sz+1))">
>>> <CHANGE quantumnumber="Sz" change="1"/>
>>> </OPERATOR>
>>> <OPERATOR name="Sminus" matrixelement="sqrt(S*(S+1)-Sz*(Sz-1))">
>>> <CHANGE quantumnumber="Sz" change="-1"/>
>>> </OPERATOR>
>>> <OPERATOR name="Sz" matrixelement="Sz"/>
>>> </SITEBASIS>
>>>
>>>
>>> <SITEOPERATOR name="Sx" site="x">
>>> 1/2*(Splus(x)+Sminus(x))
>>> </SITEOPERATOR>
>>>
>>> <SITEOPERATOR name="Sy" site="x">
>>> 1/2/I*(Splus(x)-Sminus(x))
>>> </SITEOPERATOR>
>>>
>>> <BASIS name="spin">
>>> <SITEBASIS ref="spin"/>
>>> </BASIS>
>>>
>>> <HAMILTONIAN name="kitaev">
>>>
>>> <PARAMETER name="J1" default="1"/>
>>> <PARAMETER name="Jz" default="J1"/>
>>> <PARAMETER name="Jx" default="J1"/>
>>> <PARAMETER name="Jy" default="J1"/>
>>>
>>> <BASIS ref="spin"/>
>>>
>>> <BONDTERM type="0" source="i" target="j">
>>> Jz*Sz(i)*Sz(j)
>>> </BONDTERM>
>>>
>>> <BONDTERM type="1" source="i" target="j">
>>> Jx*Sx(i)*Sx(j)
>>>
>>> </BONDTERM>
>>>
>>> <BONDTERM type="2" source="i" target="j">
>>> Jy*Sy(i)*Sy(j)
>>>
>>> </BONDTERM>
>>> </HAMILTONIAN>
>>>
>>> </MODELS>
>>>
>>> Jun
>>>
>>
>>
>

--
Jun Wen, Graduate Research Assistant
Office: RLM 7.312
Department of Physics
1 University Station C1600
The University of Texas at Austin
TX, 78712
Email: jwen@physics.utexas.edu
junwen.ut@gmail.com