December 2013 - Comp-phys-alps-users

Re: [ALPS-users] Histogram Raw Data MC Simulation
by Ionel Bogdan Guster 14 Dec '13

14 Dec '13

Dear Mr. Troyer, I was thinking about the data generated by the MC simulations, the raw data, like the generated values for energy/energy density, the number of bins, the width of the bins, the value/counts in every bin, so I can make the energy histogram for each lattice size that I would like and compare it with my own C++ simulation afterwards. I am sorry for being so vague in the previous e-mail! Thank you! Regards, Bogdan

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Histogram Raw Data MC Simulation
by Ionel Bogdan Guster 13 Dec '13

13 Dec '13

Dear all, I am a newbie in using ALPS and in learning computational physics. At this moment I am trying to compare the results from my C++ Monte Carlo simulation for the Ising model with the ALPS' ones. I would need your help in trying to find the output(raw) data for the histograms in ALPS, because I would like to compare this too. Thank you for your help! Regards, Bogdan

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Kondo lattice model
by Martin Hohenadler 10 Dec '13

10 Dec '13

Dear all, Taking the Kondo lattice model as an example which is included in the models.xml file, I was wondering how the distinction between the onsite exchange and the hopping is made. In terms of the Hamiltonian, there are sites with type 1 (itinerant fermions) and type 2 (local spins). However, both the hopping and the exchange are implemented in terms of bond operators acting between sites i and j, with the type of site not specified. Is that sufficient to ensure that the exchange acts within the two-site unit cell, i.e, between the local spin and an itinerant spin at the same lattice site? Thanks, Martin

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recompiling ALPS/looper for XYZ two-spin interaction calculations
by Nathanael Fortune 04 Dec '13

04 Dec '13

Does anyone have any advice on how to recompile the ALPS/looper package to support XYZ two-spin interactions (in addition to the already supported XXZ two-spin interactions)? A former student used the ALPS/looper packages support of XXZ two-spin interactions to carry out QMC calculations of the magnetic-field-dependent phase boundary for a S = 1/2 Heisenberg system with weak easy-plane (XY) anisotropy. Unfortunately for us, experiments experiments now reveal that the experimental system has a weak but non-negligible biaxial asymmetry within the XY plane itself, necessitating the calculation of XYZ two-spin interactions that distinguish between X and Y. See background below for details, if curious. The Todo laboratory webpage for ALPS/Looper — see http://todo.issp.u-tokyo.ac.jp/en/projects/alps-looper?set_language=en/ — notes that the application can be recompiled to provide support for XYZ two-spin interactions but I haven't yet figured out how that can be done (nor how it would be re-integrated into the full ALPS package). I would appreciate any guidance this group can provide! Best Regards, Nat Fortune background: A colleague of mine used the ALPS/looper package to carry out QMC calculations of the magnetic-field-dependent phase boundary for a S = 1/2 Heisenberg system with weak easy-plane (XY) anisotropy. He did this by setting the spin-Hamiltonian parameters Jz/Jxy = 0.995. This corresponds to $\frac{\Delta}{J} = 0.005$, where the Hamiltonian is given by the following equation: \begin{equation} H = J \sum_{nn}[S_{i}^{x} S_{j}^{x}+ S_{i}^{y} S_{j}^{y} + ( 1 -\Delta ) S_{i}^{z} S_{j}^{z}] + J_{\perp}\sum_{i,i'} \boldsymbol{S}_{i} \cdot \boldsymbol{S}_{i'}-g \mu_B \boldsymbol{H}\cdot \sum_{j}\boldsymbol{S}_j \label{eq:Xiao2009Hamiltonian} \end{equation} and the first summation is over nearest neighbors, the second summation links each spin to its counterparts in adjacent layers, and the third summation includes all spins. Unfortunately for us, experiments now reveal that the experimental system we want to model is better described by a biaxial asymmetry within the XY plane, where $\Delta = 0.003$ would be replaced by $\Delta_{z} = 0.003$ and $\Delta_{y} = 0.0003$, where the Hamiltonian is given by the following equation: \begin{equation} H = J \sum_{i,j}[S_{i}^{x} S_{j}^{x}+ ( 1 -\Delta_y ) S_{i}^{y} S_{j}^{y} + ( 1 -\Delta_z ) S_{i}^{z} S_{j}^{z}] -g \mu_B \boldsymbol{H}\cdot \sum_{j}\boldsymbol{S}_j + J_{\perp}\sum_{i,i'} \boldsymbol{S}_{i} \cdot \boldsymbol{S}_{i'} \label{eq:NewHamiltonian} \end{equation} -- Professor Nathanael Fortune, Ph.D. Department of Physics 315 McConnell Hall 44 College Lane Smith College Northampton MA 01063 nfortune(a)smith.edu (413) 585-3980 (office) (413) 585-3919 (lab) http://www.smith.edu/physics/ "The great tragedy of Science — the slaying of a beautiful hypothesis by an ugly fact." T.H. Huxley

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