February 2009 - Comp-phys-alps-users

current correlation function for fermionic hubbard model
by khalid hassan 30 May '09

30 May '09

Can alps can calculate the current correlation function for the fermionic hubbard model model for say two site. I have been using alps to calculate cahrge coorelation function the charge correlation function is < n_i n_j > = < c_i^+ c_i c_i^+ c_i > where as the current correlation function is < j_i j_j > = < c_i^+ c_j c_k^+ c_l > see the changing indexes. If it is possible then send me the program statement Best regards Khalid Loane

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alps in ubuntu hardy
by sinan bulut 17 Apr '09

17 Apr '09

Does anyone know or have experience on how to install alps in ubuntu(hardy 8.04) ? I tried to install it from the source using "configure, make ... etc" commands but it did not work.

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Operator definition
by zhian asadzadeh 28 Feb '09

28 Feb '09

Hi All, I am using DMRG for my problem, I need to calculate expectation value of Y component of Spin operator (Sy) , As a result, I need to define it in the model.xml file. How I can define it? I tried with Sy(i)=1/(2*sqrt(-1))*(Splus(i)-Sminus(i)), but I got incorrect results. I will be very appreciate if someone could help me? Thank you very much, Mohammad.

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I am using it with exact diagonalization
by khalid hassan 27 Feb '09

27 Feb '09

I am using it with exact diagonalization. If it is implemented for the exact diagonalization please give the program statement. > > Message: 2 > Date: Thu, 26 Feb 2009 14:19:05 -0800 > From: "Adrian E. Feiguin" <afeiguin(a)kitp.ucsb.edu> > Subject: Re: [ALPS-users] current correlation function for > fermionic > hubbard model > To: comp-phys-alps-users(a)phys.ethz.ch > Message-ID: <49A71559.80403(a)kitp.ucsb.edu> > Content-Type: text/plain; charset=ISO-8859-1; > format=flowed > > Hi Khalid, > > Are you using exact diagonalization, or DMRG? > > At the present, it hasn't been implemented in the DMRG > code. > > Saludos, > <ADRIAN> > > khalid hassan wrote: > > >Can alps can calculate the current correlation function > for the fermionic hubbard model model for say two site. I > have been using alps to calculate cahrge coorelation > function > > > >the charge correlation function is > > > >< n_i n_j > = < c_i^+ c_i c_i^+ c_i > > > > > >where as the current correlation function is > > > >< j_i j_j > = < c_i^+ c_j c_k^+ c_l > > > > > >see the changing indexes. > > > >If it is possible then send me the program statement > > > >Best regards > > > >Khalid Loane > > > >

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current correlation function for fermionic hubbard model using alps
by khalid hassan 27 Feb '09

27 Feb '09

I am using alps for the calculation of charge correlation function for the fermionic hubbard model. Now I want to calculate the current correlation function. the expression for the charge correlation function is < n_i : n_j > = < c_i^+ c_i : c_j^+ c_j > the expression for the current correlation function is < j_i : j_j > = < c_i^+ c_j : c_k^+ c_l > Notice the changing indices in the current expression. If it is possible then please give the program statements doing this Best Regards Khalid Loane

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Simple graphs and complex hopping parameter(t)
by Akinlolu Akande 09 Feb '09

09 Feb '09

Hi all, Is it not possible to define a simple graph with complex hopping parameter in the Hamiltonian when using fulldiagonization? For example, a 4-site chain is defined using a simple graph as <LATTICES> <GRAPH name="Chain" vertices=" 4"> <VERTEX id=" 1" type="0"></VERTEX> <VERTEX id=" 2" type="0"></VERTEX> <VERTEX id=" 3" type="0"></VERTEX> <VERTEX id=" 4" type="0"></VERTEX> <EDGE type="0" source=" 1" target=" 2"/> <EDGE type="0" source=" 2" target=" 3"/> <EDGE type="0" source=" 3" target=" 4"/> </GRAPH> </LATTICES> which I could also use the lattices.xml in the lattice libraries.I discovered that when the lattice in the libraries is used, it works well for complex hopping but using a simple graphs I got the following errors 'can not convert complex number into real one'.Any reason for this error?The reason I want to use a simple graph is because I want to use a different lattice structure for my calculations. Thanks Akin

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definition of energy density/heat capacity
by Fritz Koermann 08 Feb '09

08 Feb '09

Hi alps community, does the "Energy Density" output in the classical spinmc correspond to the (Total Energy)/spins and the analogue "Energy Density in the quantum case, e.g. using loop, to (Total Energy)/volume? Since for simple cubic systems both energy densities are equal but for a simple bcc lattice they differ by a factor of 2 so I wonder if they are differently defined? If so, does the same apply consistently to the calculated heat capacities (are they calculated using the fluctuations of the corresponding energy densities)? Best, Fritz --- Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße 1 D-40237 Düsseldorf Handelsregister B 2533 Amtsgericht Düsseldorf Geschäftsführung Prof. Dr. Jörg Neugebauer Prof. Dr. Dierk Raabe Prof. Dr. Martin Stratmann Dipl.-Kfm. Herbert Wilk Ust.-Id.-Nr.: DE 11 93 58 514 Steuernummer: 105 5891 1000 -------------------------------------------------

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Measurements
by Jakub Zakrzewski 04 Feb '09

04 Feb '09

Hello All, coould someone more experienced than me could explain briefly what type of measurements (averages of observables) may be extracted from current version. I am most interested in boson model now but question is more general. The section on parameters/measurements is unfortunately missing in wiki... Example: MEASURE_LOCAL[Local density]=n allows to get occupation of sites <n_i> for Bose-Hubbard. (Thanks, Akin, for this example). Probably other averages can be extracted but how? I tired a second moment by typing simply MEASURE_LOCAL[Local density^2]=n2 that for sparse/full diagonalization gives (e.g. sparse) Cannot evaluate expression n2(i) similarly for MEASURE_LOCAL[Compressibility]=kappa [actually in one of the files kappa(i) seems to be evaluated as it should from n2(i) and n(i) ] Worm algorithm in QMC yields: Will not measure "Compressibility" since it is off-diagonal or not a site operator Will not measure "Local density^2" since it is off-diagonal or not a site operator (which are apparently incorrect comments anyway) anybody kind enough to help? Best wishes kuba

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kinetic and potential energy
by Akinlolu Akande 03 Feb '09

03 Feb '09

Hello all, I am just curious to know whether it is possible to write out individually the kinetic energy term and potential energy term of the ground state energy using full diagonization/sparse diagonization/etc.If yes, how is it done? Best Regards. Akin

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