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1244 discussions

Accuracy of sparsediag
by epquinn＠pks.mpg.de 12 Jun '14

12 Jun '14

Greetings, I am wondering if it is possible to increase the accuracy of sparsediag, for example for the result it gives for the lowest eigenvalue. There does not appear to be a suitable input parameter. My understanding is that increasing accuracy comes at a computational cost, and I need to tweak the balance further to the side of accuracy. With best regards, Eoin

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alternative fermion Hubbard
by Fernando Iemini 12 Jun '14

12 Jun '14

dearl all, I've using the ''alternative fermion Hubbard'' model, with open boundary conditions, and analyzing its single-particle correlations, <cdag_up:c_up>. I'm not being able however to compute these observables for larger lattices, e.g., L=~160. I'm getting a "segmentation fault" message, does anybody know why is happening this error, maybe due to memory? If so, what would be good parameters in order to avoid it? Here is the script i'm using: LATTICE="open chain lattice" MODEL="alternative fermion Hubbard" CONSERVED_QUANTUMNUMBERS="N,Sz,Nup,Ndown" N_total=160 Sz_total=0 Nup_total=80 Ndown_total=80 mu=0 t=1 NUMBER_EIGENVALUES=1 L=160 MAXSTATES=100 MEASURE_CORRELATIONS[cdag_up c_up]="cdag_up:c_up" {U = 9.000000e-01,V=5.500000e-01,TRUNCATION_ERROR=1e-7} regards, Fernando.

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Unconventional hopping
by vitbka konef 05 Jun '14

05 Jun '14

Hi all, Thanks for the help. I did it, in some way! With best regards.

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Re: [ALPS-users] Comp-phys-alps-users Digest, Vol 98, Issue 6
by bondnina 01 Jun '14

01 Jun '14

Dear Michele. Thank you for your very detailed answer. I have one more question. I am afraid that the approaches you have listed in your male have only static nature. Maybe I am wrong but I didn't get how to apply t parameter depending on time. That maybe useful to simulate chain dynamics for example. Best, Nina ---------- Forwarded message ---------- From: <comp-phys-alps-users-request(a)lists.phys.ethz.ch> Date: 29 May 2014 12:00 Subject: Comp-phys-alps-users Digest, Vol 98, Issue 6 To: comp-phys-alps-users(a)lists.phys.ethz.ch Send Comp-phys-alps-users mailing list submissions to comp-phys-alps-users(a)lists.phys.ethz.ch To subscribe or unsubscribe via the World Wide Web, visit https://lists.phys.ethz.ch/listinfo/comp-phys-alps-users or, via email, send a message with subject or body 'help' to comp-phys-alps-users-request(a)lists.phys.ethz.ch You can reach the person managing the list at comp-phys-alps-users-owner(a)lists.phys.ethz.ch When replying, please edit your Subject line so it is more specific than "Re: Contents of Comp-phys-alps-users digest..." Today's Topics: 1. Exploiting degeneracy in Hybridization impurity solver (backes(a)th.physik.uni-frankfurt.de) 2. Re: Exploiting degeneracy in Hybridization impurity solver (august(a)fzu.cz) 3. Re: Variational hopping parameter (Michele Dolfi) ---------------------------------------------------------------------- Message: 1 Date: Wed, 28 May 2014 12:40:54 +0200 From: backes(a)th.physik.uni-frankfurt.de To: comp-phys-alps-users(a)lists.phys.ethz.ch Subject: [ALPS-users] Exploiting degeneracy in Hybridization impurity solver Message-ID: < c3a4761d76660198b749e13b652541aa.squirrel(a)th.physik.uni-frankfurt.de> Content-Type: text/plain;charset=utf-8 Dear Alps developers, is it possible to add an option for specifying and exploiting the degeneracy of some orbitals in the Hybridization expansion solver? E.g. for a paramagnetic calculation, where only half of the orbitals need to be measured (the input Hybridization function and interaction parameters are identical for these orbitals). best regards, Steffen Backes ------------------------------ Message: 2 Date: Wed, 28 May 2014 14:57:49 +0200 From: august(a)fzu.cz To: comp-phys-alps-users(a)lists.phys.ethz.ch Subject: Re: [ALPS-users] Exploiting degeneracy in Hybridization impurity solver Message-ID: <63da888d9fd14d678d4270331e2a4696.squirrel(a)gate.fzu.cz> Content-Type: text/plain;charset=utf-8 Hi Steffen, Do you want just symmetrize the results for equivalent orbitals at the end of your calculation or really measure only on of the equivalent G. functions and ignore the rest? If I understand correctly, you dont gain anything by not measuring say down-spin orbitals in a paramagnetic system since the spin equivalence is broken during the simulation. Full measurement is therefore slower but leads to a better statistics. Best regards, Pavel > Dear Alps developers, > > is it possible to add an option for specifying and exploiting the > degeneracy of some orbitals in the Hybridization expansion solver? E.g. > for a paramagnetic calculation, where only half of the orbitals need to be > measured (the input Hybridization function and interaction parameters are > identical for these orbitals). > > best regards, > Steffen Backes > > ------------------------------ Message: 3 Date: Wed, 28 May 2014 09:16:46 -0400 From: Michele Dolfi <dolfim(a)phys.ethz.ch> To: comp-phys-alps-users(a)lists.phys.ethz.ch Subject: Re: [ALPS-users] Variational hopping parameter Message-ID: <C16EA761-87AF-4E04-B966-4F861E887659(a)phys.ethz.ch> Content-Type: text/plain; charset="windows-1252" Dear Nina, In the latest release of ALPS 2.2.0b3 we introduced a new set of codes based on MPS. These codes use the ALPS model and lattice library, therefore there is not no problem running this kind of simulations. To do so: 1. you need to create a custom lattice with a different type for each bond. https://alps.comp-phys.org/mediawiki/index.php/Tutorials:LatticeHOWTO 2. the model ?fermion Hubbard? is already able to handle different hopping amplitudes, just specify all values with the parameters t0=?, t1=?, ? where the number correspond to the bond type you specified in the lattice 3. finally you can setup a simulation using the new mps_evolve code. the easiest is to look at the mps-05 and mps-06 tutorials to have an idea on how to run the code. Best regards, Michele -- ETH Zurich Michele Dolfi Institute for Theoretical Physics HIT G 32.4 Wolfgang-Pauli-Str. 27 8093 Zurich Switzerland dolfim(a)phys.ethz.ch www.itp.phys.ethz.ch +41 44 633 78 56 phone +41 44 633 11 15 fax On 27 May 2014, at 18:30, Michael Wall <mwall.physics(a)gmail.com> wrote: > Dear Nina, > > The TEBD code in ALPS is not set up for site-dependent Hubbard parameters. Some of the other ALPS developers may be able to answer better whether such functionality will be added in near-term ALPS MPS codes. If not, Open Source MPS can perform the sorts of calculations you want to do, and eventually will become part of ALPS. > > -Michael > > > > > On Fri, May 23, 2014 at 2:02 AM, bondnina <bondnina(a)gmail.com> wrote: > Hi dear Alps users. > I wonder is there any possibility to setup different hopping parameters for each site in the Hubbard chain and evaluate such a system using TEBD technic. > Thank you for help. > > -- > Yours sincerely, Nina Bondarenko > 1024R/EAC56154 9F6C DDF8 6873 5D19 FF9A 600E 46A4 42BE EAC5 6154 >

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Variational hopping parameter
by bondnina 28 May '14

28 May '14

Hi dear Alps users. I wonder is there any possibility to setup different hopping parameters for each site in the Hubbard chain and evaluate such a system using TEBD technic. Thank you for help. -- Yours sincerely, Nina Bondarenko 1024R/EAC56154 9F6C DDF8 6873 5D19 FF9A 600E 46A4 42BE EAC5 6154

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Exploiting degeneracy in Hybridization impurity solver
by backes＠th.physik.uni-frankfurt.de 28 May '14

28 May '14

Dear Alps developers, is it possible to add an option for specifying and exploiting the degeneracy of some orbitals in the Hybridization expansion solver? E.g. for a paramagnetic calculation, where only half of the orbitals need to be measured (the input Hybridization function and interaction parameters are identical for these orbitals). best regards, Steffen Backes

2 1

Numerical precision in large Lanczos problems
by Alex Petrescu 12 May '14

12 May '14

Hello ALPS fellows, I encountered constraint-breaking numerical errors in two-point correlation functions evaluated by ALPS on long eigenvectors [sparsediag in ALPS 2.1]. Correlation functions evaluated are <n(i) n(j)> - <n(i)><n(j)> and <bdag(i) b(j)> in a Bose-Hubbard model. I looked at a *large problem*, 18 site lattice (4.9 x 10^6 states with U(1) and translation sym) and a *small problem*, 12 site lattice (~12300 states with the same symmetries). Large problem results are inconsistent* for some non-negligible parameter subset* with those for the small problem. The inconsistency is worse typically where most eigenvector entries are expected to vanish. <n(i)^2> - <n(i)>^2 can become large negative and the set <n(i)> may not obey the constraint on total boson number; the Green's function <bdag(i) b(j)> can occasionally vanish identically. This does not happen everywhere, but on a large parameter subset. Small problem correlation functions are as expected from alternative calculations. Questions: 1) Would this issue be caused by numerical precision problems when the vector gets large? If so, what are the possible flags to pass to sparsediag? 2) A quick look at sparsediag source shows that value_type is either complex<double> or double. This seems to be changeable to <long double>. Are there any other places you might think of that would allow me to build a long double or (complex<long double>) Hamiltonian? Thank you and regards, Alexandru Petrescu

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dynamical correlation functions
by Stefano Di Sabatino 11 May '14

11 May '14

Dear ALPS users, is it possible to obtain from sparsediag or fulldiag, dynamical correlation functions? In particular I'm interested in green functions to compute spectral functions in terms of the frequency. Thanks, Stefano

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Problem building ALPS from source
by Niraj Ghimire 08 May '14

08 May '14

Dear alps users, I have been trying to build alps from source on Fedora 20. I could get the dependent libraries and tools from the instructions page but I have been having issues trying to build alps using a source package. I unpacked the source package and tried to use cmake from the basic instruction given on "Build ALPS" section but I kept getting errors. Since I am a beginner for linux OS, I would really appreciate if there is sufficient information (step-by-step instructions) on "Build ALPS" section. Thank you, Niraj

2 1

Unconventional hopping
by vitbka konef 23 Apr '14

23 Apr '14

Dear ALPS users, I have question related with the Worm method. Does anybody know how add this hoppings : t1*(S_{i+}T_{j-}+S_{i-}T_{j+}) and t2*(T_{i+}T_{j-}+T_{i-}T_{j+}) , where T_{i+-}=S_{iz}S_{i+-}+S_{i+-}S_{iz}?

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