Comp-phys-alps-users

comp-phys-alps-users@lists.phys.ethz.ch

February 2007

4 participants
2 discussions

Re: [ALPS-users] ALPS questions: triangular lattice basis vectors, spatially anisotropic model
by Simon Trebst 16 Feb '07

16 Feb '07

Dear Fa, thanks for your email. (1) Indeed the second vector in the triangular lattice description is incorrect and should be replaced by <VECTOR>a/2 a*sqrt(3)/2</VECTOR> We have changed this in the code repository (it will become available with the next release). So please update this line in your current files for the time being. (2) Yes, you can already implement spatially anisotropic models with different interaction terms on different types of bonds. The <BONDTERM> has a type-variable which allows this. Here is an example from the model library how-to webpage (http://alps.comp-phys.org: 16080/wiki/index.php/Tutorials:ModelHOWTO) for a Bose Hubbard model: <HAMILTONIAN name="hardcore boson"> <PARAMETER name="mu" default="0"/> <PARAMETER name="t" default="1"/> <PARAMETER name="t'" default="1"/> <BASIS ref="hardcore boson"/> <SITETERM type="0"> -mu*n </SITETERM> <BONDTERM type="0" source="i" target="j"> -t*(bdag(i)*b(j)+bdag(j)*b(i))) </BONDTERM> <BONDTERM type="1" source="i" target="j"> -t'*(bdag(i)*b(j)+bdag(j)*b(i))) </BONDTERM> </HAMILTONIAN> If you implement a new (triangular) lattice with two different type of bonds, e.g. "0" and "1", and implement your Hamiltonian similar to the one above, will you be able to study the model you are interested in? Please let me know, and we can further assist you Simon PS: I have copied this email to the ALPS user mailing list. > Dear Dr. Trebst > > I'm a graduate student in physics department at berkeley. > Currently i'm trying to learn to use the ALPS library and > application and have met some problems. > > I'm not sure whether you are the right person to contact. > If not, please ignore the following and take my apology. > > (1). In the lattices.xml library, the triangular lattice is > <LATTICE name="triangular lattice" dimension="2"> > <PARAMETER name="a" default="1"/> > <BASIS> > <VECTOR>a 0</VECTOR> > <VECTOR>a*sqrt(3)/2 a/2</VECTOR> > </BASIS> > <RECIPROCALBASIS> > <VECTOR>0 4*pi/a/sqrt(3)</VECTOR> > <VECTOR>2*pi/a -2*pi/a/sqrt(3)</VECTOR> > </RECIPROCALBASIS> > </LATTICE> > > The 2nd basis vector (a*sqrt(3)/2, a/2) doesn't look correct to > me. Or > maybe I misunderstood how it is represented. > > (2). In the tutorial I can't find out how to make spatially > anisotropic model. For example, anisotropic triangular Heisenberg > antiferromagnet. > It seems that the <BONDTERM> doesn't care the type of bond, or > the type of source/target sites. > Does this kind of feature have been incorporated into the > applications, > or do I have to write my own code to implement this? > > Thank you for your help. > > Best regards. > > ~Fa

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Modifying input in the DMRG program
by Christopher Brust 16 Feb '07

16 Feb '07

Hi. I'm a student doing research on Heisenberg spin chains, and I'm attempting to get ground state energies for longer chains than my group has done before. I've been running the DMRG program included with ALPS (not the 'simple' one) with a parameter file that looks something like: MODEL = "spin" LATTICE = "chain lattice" LATTICE_LIBRARY = "../lattices.xml" MODEL_LIBRARY = "../models.xml" CONSERVED_QUANTUMNUMBERS = "Sz" local_S = 1/2 J = 1 V = 0 SWEEPS = 30 MAXSTATES = 60 OUTPUT_LEVEL = 1 {L = 30} I've been able to successfully run the program, though I'm not entirely sure that all the parameters I've specified are the right ones (and that it's not just reverting to the defaults). I've been unable to find any documentation on how this particular implementation of the program works, so can anyone tell me if I'm off to the right start? In addition, I'd like to be able to run this program with site-dependent interaction coefficients (such as J = 3*k) or so, but after much tinkering, I've been unable to find the variable 'k' that represents position on the lattice. My question is is this even possible? If so, how? Should I instead be trying to modify the source code for the program and recompile it? Thanks for your time.

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