May 2016 - Comp-phys-alps-users - lists.phys.ethz.ch

a question of external potential in MPS
by 北尘心 28 May '16

28 May '16

Previously, I used DMRG to calculate the model containing the external potential, but now I would like to try to use MPS to calculate it.When i use MPS, I meet a question of potential. My potential setting like this <SITETERM site="i"> <PARAMETER name="mu#" default="mu"/> <PARAMETER name="U#" default="U"/> <PARAMETER name="Vout" default="0"/> -mu#*n(i)+U#*n_up(i)*n_down(i)+Vout*((x-(L-1)/2.0)^2)*n(i) </SITETERM> I use the model ,lattice and command like I used in DMRG, but the computer prompt like : Exception thrown: Cannot evaluate x By using DMRG, it can be calculated correctly, but MPS will prompt the error, i wonder what should I do to correct it? It is highly grateful for your any suggestion. Yours sincerely, Xingbo Wei Zhejiang Normal University Jinhua,230014, China

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infinite lattice size and initial states definitions.
by 梁霄 28 May '16

28 May '16

ALPS users and developers, I have two questions about the definitions of lattice sizes and the initial states for mps_optim. 1, how to create a infinite size of lattice? And how to define filling of the lattice for DMRG or MPS? 2, if the lattice size is finite and is very large, how to quickly set the quantumnumbers of the initial state for all sites? Thanks. Xiao Liang

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strange chemical potential of extended boson hubbard model
by 梁霄 27 May '16

27 May '16

ALPS users and developers, I am trying to calculate the phase diagram of extended boson hubbard using dmrg. The lattice is the finite one-dimension lattice with open boundaries. The chemical potentials are: u-=E(N)-E(N-1), u+=E(N+1)-E(N). E(N) is the ground energy for a total particle number N. However I found that there is something unusual when calculating the chemical potential: E(N+1)-E(N). When V is not zero, the u+ calculated by DMRG, sparsediag and mps_optim is less than the expected value. For example when L=100, N=50, t=0 and V=0.4, the correct value of u+ is 0.8, however using dmrg(mps and sparsediag) the value is 0.4 . I can obtain the correct value using u+=E(N+2)-E(N+1) when choosing L=41 and N=21 instead. However within L=101 and N=101, even choose u+=E(N+2)-E(N+1) the result is still 0.4. It seems that when V does not equal to zero the calculated chemical potential is related to specific total particle numbers. Xiao Liang

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Help with install
by Thornton, Curtislee 26 May '16

26 May '16

Hello my name is Curtis, (My setup: Windows 10 pro 64bit, Python(x,y) which is python 2.7 32bit) I am trying to install ALPS and I am running into the problem with the PATH being too long. I read everything on the website and searched google and youtube for anything I can find but still nothing helps. I tried version 2.1 and 2.2 (32 and 64 bit versions) binary installer. I tried installing it to PATH from the beginning but get the error, I then tried installing it and adding to the PATH (through the windows setting) later (I tried adding every folder to the PATH seperatly as well) and still does not 'see' it when I try to "import pyalps" and tells me there is no module with that name. I also tried setting the path inside the program 'Spyder' (IDE) which I run python with. I also tried to copy and paste the files from the ALPS install into the C:\python27 folders that hold the same file types (Dlls, Lib, libs, and include). When I copy them over I then tried to "import pyalps" again and it finds the module but then throws an error saying that some other module was not found. Any help with this will be great. Thanks for your time.

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Measuring a sum (or sum squared) of site operators
by Larry Engelhardt 14 May '16

14 May '16

Is there a way to directly measure sums of site operators and squares of sums of site operators? (I am using the directed loop SSE code, but I think this question also applied to other algorithms.) I could accomplish this indirectly by measuring the local site operators and also measuring correlations between the site operators and then adding them together (to manually expand the square), but if there is a way to do this directly, that would seem to be a more elegant/pretty solution. The motivation for this questions is that I need to compute the “Magnetization" and “Magnetization Squared” — which already exists as pre-created measurements — but my system has site dependent g values, so instead of measuring the sum of Sz_i (the square of the sum), I need to measure the sum of g_i***Sz_i (and the square of the sum), where the sum extends over all sites, i. Is this possible? If so, can you provide an example? Thanks! Larry

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Constraints from two types of sitebasis
by 梁霄 08 May '16

08 May '16

Dear all, Recently I am using ALPS simulating JCH model. To construct the basis for atom-light interaction, two types of basis are defined on each site. My question is how to set a constraint of the summation from two types of basis? For example, <BASIS> <SITEBASIS type="0" ref="M"/> <SITEBASIS type="1" ref="N"/> <CONSTRAINT quanumnumber="A+B" value="C"/> </BASIS> A and B are from sitebasis M and N. Does the method above work? Thanks.

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Define a J-C model
by 梁霄 06 May '16

06 May '16

Dear all, In alps models all the basis are defined on site positions. When there are interactions between atoms and photons, an atom on each site can absorb or emit photons, how to define such basis for photons? Thanks.

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ALPS
by Albert Young 05 May '16

05 May '16

Dear Sir/Madam: I am using ALPS now, but I have a question, can I add a new lattice to lattice.xml ? I did it, however, I was denied the right to do some change? What should I do ? best wishes ! Albert Young

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Questions about t and t#
by 梁霄 01 May '16

01 May '16

Hello, In model.xml file, the Boson Hubbard model has the tunneling parameter "t", however in the bondterm "-t#*( bdag(i)b(j)+bdag(j)b(i) )" the parameter is defined as "t#" and its default value is zero. When the tunneling parameter is defined by "t" in python or command line, will it be any difference if I change the default value of "t#" into "t" in model.xml file? Thanks. Xiao Liang

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