Dear All,
I'm using ALPS DMRG (MPS) to study the magnetism of XY model in a frustrated chain.
In order to obtain the Sx correlation functions, I add the following command line: MEASURE_CORRELATIONS[Sx_correlation]= Sx
I expected that the output file presented me all <Sx(i) Sx(j)> correlation functions. However, there were only this line in the output file.
<SCALAR_AVERAGE name="Sx_correlation"><MEAN>6.7066684180584175e-317</MEAN></SCALAR_AVERAGE>
Even when I chose to program make only specifics calculations, such as
MEASURE_LOCAL_AT[SxSx_corr] = "Sx:Sx|(0,1),(0,2),(0,3),(0,4)"
the answer I obtained was zero, no matter of the choice of the external parameters, as showed below.
<VECTOR_AVERAGE name="SxSx_corr"> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
*(the index are not the same in the input and output file because I'm working with a unit cell with 3 sites.)
Owing to these not good results, I did a test, and then I measured the correlation functions <Splus(i) Splus(j)>, <Splus(i) Sminus(j)> and <Sminus(i) Sminus(j)>, as showed below
MEASURE_LOCAL_AT[SxSx_corr1] = "Splus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr2] = "Splus:Sminus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr3] = "Sminus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr4] = "Sminus:Sminus|(3,18)"
and I obtained
<VECTOR_AVERAGE name="SxSx_corr1"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.1565028679350004</MEAN></SCALAR_AVERAGE>
</VECTOR_AVERAGE> <VECTOR_AVERAGE name="SxSx_corr2"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820933</MEAN></SCALAR_AVERAGE>
</VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr3"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820814</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr4"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15650286793499901</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
which means that <SxSx>'s are really nonzero. Actually, these last results are in good agreement with exact diagonalization for a small chain. (Before you asked me, I correctly defined the onsite operator Sx in the model library.)
Then, probably it could be a bug when the program is summing the terms of SxSx correlations.
I really thank you for this great program.
Regards,
Natanael C. Costa
Dear Nathanael,
Sx correlations are currently supported only when no quantum numbers are conserved.
This has to do with the internal representation of the site operators, which requires a single change in the the quantum number basis.
Best regards, Michele
-- ETH Zurich Michele Dolfi Institute for Theoretical Physics HIT G 32.4 Wolfgang-Pauli-Str. 27 8093 Zurich Switzerland
dolfim@phys.ethz.ch www.itp.phys.ethz.ch
+41 44 633 78 56 phone +41 44 633 11 15 fax
On 05 Sep 2016, at 06:44, Natanael de Carvalho Costa natanael@if.ufrj.br wrote:
Dear All,
I'm using ALPS DMRG (MPS) to study the magnetism of XY model in a frustrated chain.
In order to obtain the Sx correlation functions, I add the following command line: MEASURE_CORRELATIONS[Sx_correlation]= Sx
I expected that the output file presented me all <Sx(i) Sx(j)> correlation functions. However, there were only this line in the output file.
<SCALAR_AVERAGE name="Sx_correlation"><MEAN>6.7066684180584175e-317</MEAN></SCALAR_AVERAGE>
Even when I chose to program make only specifics calculations, such as
MEASURE_LOCAL_AT[SxSx_corr] = "Sx:Sx|(0,1),(0,2),(0,3),(0,4)"
the answer I obtained was zero, no matter of the choice of the external parameters, as showed below.
<VECTOR_AVERAGE name="SxSx_corr"> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
*(the index are not the same in the input and output file because I'm working with a unit cell with 3 sites.)
Owing to these not good results, I did a test, and then I measured the correlation functions <Splus(i) Splus(j)>, <Splus(i) Sminus(j)> and <Sminus(i) Sminus(j)>, as showed below
MEASURE_LOCAL_AT[SxSx_corr1] = "Splus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr2] = "Splus:Sminus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr3] = "Sminus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr4] = "Sminus:Sminus|(3,18)"
and I obtained
<VECTOR_AVERAGE name="SxSx_corr1"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.1565028679350004</MEAN></SCALAR_AVERAGE>
</VECTOR_AVERAGE> <VECTOR_AVERAGE name="SxSx_corr2"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820933</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr3"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820814</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr4"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15650286793499901</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
which means that <SxSx>'s are really nonzero. Actually, these last results are in good agreement with exact diagonalization for a small chain. (Before you asked me, I correctly defined the onsite operator Sx in the model library.)
Then, probably it could be a bug when the program is summing the terms of SxSx correlations.
I really thank you for this great program.
Regards, Natanael C. Costa
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You can measure S+S- correlation functions, which may also be useful. From them (and potentially S=S= and S-S- if there is no U(1) symmetry) you can get the SxSx correlation function
On 05 Sep 2016, at 11:27, Michele Dolfi dolfim@phys.ethz.ch wrote:
Dear Nathanael,
Sx correlations are currently supported only when no quantum numbers are conserved.
This has to do with the internal representation of the site operators, which requires a single change in the the quantum number basis.
Best regards, Michele
-- ETH Zurich Michele Dolfi Institute for Theoretical Physics HIT G 32.4 Wolfgang-Pauli-Str. 27 8093 Zurich Switzerland
dolfim@phys.ethz.ch mailto:dolfim@phys.ethz.ch www.itp.phys.ethz.ch http://www.itp.phys.ethz.ch/
+41 44 633 78 56 phone +41 44 633 11 15 fax
On 05 Sep 2016, at 06:44, Natanael de Carvalho Costa <natanael@if.ufrj.br mailto:natanael@if.ufrj.br> wrote:
Dear All,
I'm using ALPS DMRG (MPS) to study the magnetism of XY model in a frustrated chain.
In order to obtain the Sx correlation functions, I add the following command line: MEASURE_CORRELATIONS[Sx_correlation]= Sx
I expected that the output file presented me all <Sx(i) Sx(j)> correlation functions. However, there were only this line in the output file.
<SCALAR_AVERAGE name="Sx_correlation"><MEAN>6.7066684180584175e-317</MEAN></SCALAR_AVERAGE>
Even when I chose to program make only specifics calculations, such as
MEASURE_LOCAL_AT[SxSx_corr] = "Sx:Sx|(0,1),(0,2),(0,3),(0,4)"
the answer I obtained was zero, no matter of the choice of the external parameters, as showed below.
<VECTOR_AVERAGE name="SxSx_corr"> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 0 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> <SCALAR_AVERAGE indexvalue="( 0 ) -- ( 1 )"><MEAN>0</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
*(the index are not the same in the input and output file because I'm working with a unit cell with 3 sites.)
Owing to these not good results, I did a test, and then I measured the correlation functions <Splus(i) Splus(j)>, <Splus(i) Sminus(j)> and <Sminus(i) Sminus(j)>, as showed below
MEASURE_LOCAL_AT[SxSx_corr1] = "Splus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr2] = "Splus:Sminus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr3] = "Sminus:Splus|(3,18)" MEASURE_LOCAL_AT[SxSx_corr4] = "Sminus:Sminus|(3,18)"
and I obtained
<VECTOR_AVERAGE name="SxSx_corr1"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.1565028679350004</MEAN></SCALAR_AVERAGE>
</VECTOR_AVERAGE> <VECTOR_AVERAGE name="SxSx_corr2"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820933</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr3"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15912792472820814</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
<VECTOR_AVERAGE name="SxSx_corr4"> <SCALAR_AVERAGE indexvalue="( 1 ) -- ( 6 )"><MEAN>-0.15650286793499901</MEAN></SCALAR_AVERAGE> </VECTOR_AVERAGE>
which means that <SxSx>'s are really nonzero. Actually, these last results are in good agreement with exact diagonalization for a small chain. (Before you asked me, I correctly defined the onsite operator Sx in the model library.)
Then, probably it could be a bug when the program is summing the terms of SxSx correlations.
I really thank you for this great program.
Regards, Natanael C. Costa
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