Comp-phys-alps-users

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1244 discussions

Winding numbers
by "Michał Maik" 13 Apr '10

13 Apr '10

Hi, I am having a problem calculating the "Winding Number vs Energy" graph for certain models. When I do it for the "4-site mixed" I am not able to get it to work but if I use a "square lattice" with L=2 it seems to work fine. I am wondering how I have to define a model in order to calculate the winding numbers. Regards Michal Maik

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Call for Papers: International Workshop on "Statistical Physics of Quantum Systems" (Tokyo, August 2-4 2010)
by Synge Todo 04 Mar '10

04 Mar '10

International Workshop on "Statistical Physics of Quantum Systems" First Announcement and Call for Papers We cordially invite you to attend and/or present a paper at the International Workshop on Statistical Physics of Quantum Systems held during 2-4 August 2010 at Institute of Industrial Science, University of Tokyo. http://www.iis.u-tokyo.ac.jp/access_e/access_e.html (In the convention hall of the An block of the campus.) http://www.iis.u-tokyo.ac.jp/access_e/campusmap_e.html This is a satellite meeting of the international conference STATPHYS 24 http://www.statphys.org.au/ In this workshop, we will discuss on the recent developments of studies on various novel properties of strongly interacting quantum systems, non-equilibrium quantum dynamics under time-depending fields, and quantum response as well as other related topics. Specific topics include, but not restricted to a.. Phase transitions in quantum systems b.. Novel quantum properties in the ground state c.. Quantum dynamics d.. Quantum transport phenomena e.. Quantum information processing We ask you to register and/or submit a paper at the following web site: http://looper.t.u-tokyo.ac.jp/spqs2010/ The registration will be open by 8 March, 2010. The deadline of registration and/or submission is 30 April, 2010. We will choose poster presentations as well as a small number of oral presentations from the submitted papers and tell the authors the decision by 1 June, 2010. The registration fee is 20,000 yen (JPY20,000) for regular participants and 10,000 yen (JPY10,000) for students. It includes the attendance as well as the abstract book/CD. Please pay the fee in cash at the on-site registration desk when you arrive at the workshop. (Sorry, we do not accept credit cards.) We will have a party on the night of 3 August. The fee for the party is 5,000 yen for regular participants and 2,000 yen for students. We will collect the fee at the workshop site. Confirmed invited speakers include M. Batchelor (Australian National University, http://wwwmaths.anu.edu.au/~murrayb/Murray_Batchelor2.html) O. Cepas (Grenoble, CNRS, http://perso.neel.cnrs.fr/olivier.cepas/) G. Ordonez (Butler University, http://www.butler.edu/physics/faculty-staff) T. Petrosky (University of Texas, http://order.ph.utexas.edu/people/Petrosky.htm) H.A. De Raedt (University of Groningen, http://www.rug.nl/staff/h.a.de.raedt/index) M. Troyer (ETH, http://www.itp.phys.ethz.ch/people/troyer) G. Vidal (University of Queensland, http://www.physics.uq.edu.au/people/vidal/) T. Xiang (Chinese Academy of Sciences, http://power.itp.ac.cn/~txiang/) Local Organizers: S. Miyashita, N. Hatano, M. Imada, N. Kawakami, N. Kawashima, A. Kuniba, H. Nishimori, M. Oshikawa, T. Sakai, and S. Todo

1 0

sigma_y interaction
by Fernando Cucchietti 28 Feb '10

28 Feb '10

Hello, I probably know the answer to this already, but just wanted to check: I would like to use the Montecarlo code to simulate a system with a Hamiltonian that has the Sy operator, that is Sy=-I/2(Splus-Sminus). The worm and sse codes return a runtime error "can not convert complex number into real one". If I don't include de I constant (or (0.,1.) ) in the model.xml file the code starts, but then complains that it cannot simulate this term (which without the complex unit is non-Hermitian). I cannot rotate my basis because I also have the Sx operator, so I am stuck with Sy. Is there a way to do this? It looks like a no-no... Thanks Fernando -- ============================== Fernando Cucchietti Research Fellow ICFO-Institut de Ciencies Fotoniques Mediterranean Technology Park Av. Canal Olimpic s/n 08860 Castelldefels (Barcelona), Spain ============================== 1+1=3, for large values of 1 ------------------------------

2 1

Exact Diagonalization for Bose-Hubbard
by Vipin Varma 19 Feb '10

19 Feb '10

Hi I am trying the Lanczos method for solving the Bose-Hubbard model on a square lattice, to get the t/U dependence of the ground state energy per site. I tried a simple 2x1 cluster with open and periodic boundary conditions and I get a linear dependence for the energy on t/U; analytically (which I am reasonably sure is correct), I get a parabolic dependence for the energy on t/U, if I consider 2 bosons over 2 sites. Here is my parameter file: /////////////////////////// LATTICE_LIBRARY="../lattices.xml"; LATTICE="square lattice"; MODEL_LIBRARY="../models.xml"; MODEL="boson Hubbard"; U = 1; Nmax = 2; L=2; W =1; {t=0.1;} {t=0.01;} {t=0.02;} {t=0.03;} {t=0.04;} {t=0.05;} {t=0.06;} {t=0.07;} {t=0.08;} {t=0.09;} /////////////////// I have tried Nmax = 2,4,6, but all give me a linear dependence; also strangely, the energy range does not change much when I vary the value of U by orders of magnitude. I guess I am missing something simple. Any ideas will be appreciated. Vipin

2 5

Python distributions
by Matthias Troyer 05 Feb '10

05 Feb '10

Dear ALPS developers and users, Since ALPS 2.0, to be released later this year in a beta version, will rely heavily on Python for data analysis I want to start a survey about the Python distributions you are using. We might be able to prepare compiled binary installation packages for the most common combinations of OS/compiler/Python distribution. Please reply to the list with the Python distribution you are using if you feel strongly about that distribution you are using now and don't want to change it when using ALPS 2.0 in the future. Matthias PS: you will always be able to compile ALPS from source against any distribution, but many people prefer the new binary installations that can be installed in less than a minute.

6 15

unit of temperature in the extended bose-hubbard model
by Fu-Jiun Jiang ITP 25 Jan '10

25 Jan '10

hello In the extended bose-hubbard model, what's the unit for the temperature T? Is it true that when one lets V = 1 (V is the nearest-neighbor repulsive interaction), then T = 0.01 really stands for T = 0.01/V? Thanks. Sincerely, Fu-Jiun

1 0

full diagonalization with antiperiodic BCs
by jessica.alfonsi＠unipd.it 20 Jan '10

20 Jan '10

Hi everyone, I have posted some days ago about full diagonalization with antiperiodic boundary conditions for a Hubbard chain but I havent't received no answer yet. Maybe I was not much clear with my question. The point with my question is that I'd like to specify antiperiodic boundary conditions for some specific sites (i.e. a bond term t#*fermion_hop(1,N), where sites 1 and N are the chain ends) in the input model xml file. This means that the terms related to boundary conditions have to be specified separately from the usual bond terms with fermionic hopping. Is it possible to do that in the xml model file ? How can I do that in a C++ code compiled against ALPS libraries ? This would be very important for specifying lattices and models with the highest flexibility, since later I'd like to write a matrix free ED code for my 2D custom lattice... Could you give me some insight please ? Best regards Jessica Alfonsi -- Dr.ssa Jessica Alfonsi Dipartimento di Scienze Chimiche Università di Padova via Marzolo 1 35100 Padova (Italy) +39 0498275726 e-mail jessica.alfonsi(a)unipd.it

2 1

Spliting total energy
by Akinlolu Akande 19 Jan '10

19 Jan '10

Hi all, Is it possible to split the total energy calculated by alps into their individual components? For example, in the case of the Hubbard model I will want to know how to split the kinetic energy and the potential energy terms in ALPS code.u know the total hamiltonian H=H_hopping(Kinetic term)+H_U(potential term), when one does the exact diagonization or DMRG,it gives the total energy but I want to calculate the individual energy. Can anyone help? Thanks. Akin

2 1

exact diagonalization with antiperiodic BCs
by jessica.alfonsi＠unipd.it 18 Jan '10

18 Jan '10

Dear ALPS team, I have successfully performed a full diagonalization for a Hubbard chain with periodic boundary conditions using the included models in xml files. Now, I'd like to perform the same task with antiperiodic boundary conditions (a fermionic hopping with opposite sign) at chain ends, or more generally with exponetial complex phase, possibly by using again the xml input schema. Can you give me some hint ? Is it also possible to specify the hamiltonian or any other operator in a more extended form, with the site indices explicitly defined in the expression, as one would do with Mathematica, such as for instance -t#*fermion_hop(1,2) + t#*fermion_hop(3,4) + ... and so on ? Thank you for your support Best regards Jessica Alfonsi

1 0

Classical MC for
by Andrew James 15 Jan '10

15 Jan '10

Hi, I'd like to use the classical Monte Carlo code to study the properties of the 'Heisenberg-XY' model, where the symmetry is a product of O(3) and O(2), i.e. the degrees of freedom at each site can be represented by (n, \theta) where n is a vector and \theta is an independent angle. Is it feasible to do this by editing the current mc/spin files alone? From inspection it seems that, at the very least, I would need to change parts of spinmc_factory.C and create something similar to the file on.h, but allowing for O(a) * O(b) symmetry. Thanks for any advice you can give, Andrew

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Comp-phys-alps-users