June 2014 - Comp-phys-alps-users

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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