[ALPS-users] diagonal correlations

[Michele Dolfi]

Hello,

Could you please be a bit more specific about the application you are running?

You are right about the local measurement, but you need MEASURE_LOCAL, since you want to value at each site. Since the n_i^2 operator is not yet defined in the model library, you need to add it yourself. Basically I would do as follow:
1. Copy the file models.xml from ALPS_ROOT/lib/xml/models.xml, where ALPS_ROOT is the root location of your alps installation.

2. Add this definition to your local copy, it defines the n^2 operator
<SITEOPERATOR name=“n_squared" site="x">
  n(x)*n(x)
</SITEOPERATOR>

3. In your input parameters you have now to link to your new model file.
MODEL_LIBRARY=“path/to/models.xml”

4. And add your measurement
MEASURE_LOCAL[Density^2] = “ n_squared"


Hope this helps.

Best,
Michele

--
ETH Zurich
Dr. Michele Dolfi
Institute for Theoretical Physics
HIT G 32.4
Wolfgang-Pauli-Str. 27
8093 Zurich
Switzerland

dolfim at phys.ethz.ch
www.itp.phys.ethz.ch

+41 44 633 78 56 phone
+41 44 633 11 15 fax 

> On 6 Feb 2017, at 07:26, Robertson Esperanza <robbie.esperanza at gmail.com> wrote:
> 
> Hello,
> 
> I only started studying many-body physics, so there might be gaps in my knowledge. When using the MEASURE_CORRELATION, why does the measurement goes for only site i<j, is it because there will be "blowing up"? 
> 
> Alternatively, to measure for i=j, i think I could use MEASURE_AVERAGE, of let's say (n_i)^2 where n - n_up + n_down. How could I define such measurement, where you use an operator successively? Thank you for replying
> 
> Robertson Esperanza
> 
> 
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