Dear Matthias,
by \Sigma_{i,j}, I mean \sum_{i,j},
for the exact result, we know the model is integrable, so by fermionization and finally diagonalizing the Hamiltonian we will end up to an Hamiltonian with sum over independent modes, H=\sum_{k} E(k) (2 a_{k}^{dagger} a_{k}-1)
for the T=0 ground state energy, I have compared with DMRG results which are exactly same, so I am sure up to this point the form of E(k) and my summation over k space is correct.
so finally for E(T) simply we have: E(T)=\sum_{k} E(k)(2*n(k,T)-1) in which n(k,T)=1/(exp(E(k)/T)+1) ::with Boltzmann constant=1
Regards, Zhian.
On Sun, Jul 24, 2011 at 12:00 PM, < comp-phys-alps-users-request@lists.phys.ethz.ch> wrote:
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Today's Topics:
- Quantum Monte Carlo for Ising in transverse field (zhian asadzadeh)
- Re: Quantum Monte Carlo for Ising in transverse field (Matthias Troyer)
Message: 1 Date: Sat, 23 Jul 2011 16:29:39 +0200 From: zhian asadzadeh zhian.asadzadeh@gmail.com Subject: [ALPS-users] Quantum Monte Carlo for Ising in transverse field To: comp-phys-alps-users@lists.phys.ethz.ch Message-ID: <CAEw6G6sPavSO0RMreyy701xo+LN4M4LGrBzOLJkonEKs9S=Wkw@mail.gmail.com
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Dear Matthias,
my intention is doing finite T QMC for 2D ising in transverse field with the following Hamiltonian: H=-J \Sigma_{i,j} S_{i}^{z} S_{j}^{z}-h \Sigma_{i} S_{i}^{x} but for checking the accuracy of the numeric I did some checks for 1D case which we can have an exact results, probably I am expecting too much accuracy, for example:
L=100, T=0.32859 Exact:: E(T)=-105.29789708270407, Mx(T)=0.27030367598168420 looper:: E(T)=-105.61795 (0.00554), M(T)=0.4093185 (0.000138) ( I think it is in z direction) with SWEEPS:6000000, THERMALIZATION=2000000
I have checked also for other sizes and very large SWEEPS.I don't expect to get exact result but I need much more accuracy in the calculated energy.
and also other question: that magnetization which looper calculates isin the z direction? can I also measure M_{x} just with declaring it in parm file?
Thanks a lot, Zhian.On Sat, Jul 23, 2011 at 12:00 PM, < comp-phys-alps-users-request@lists.phys.ethz.ch> wrote:
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Today's Topics:
- restarting Lanczos iteration (jessica.alfonsi@unipd.it)
- Quantum Monte Carlo for Ising in transvers field (zhian asadzadeh)
- Re: Quantum Monte Carlo for Ising in transvers field (Matthias Troyer)
- Re: restarting Lanczos iteration (Matthias Troyer)
Message: 1 Date: Fri, 22 Jul 2011 12:22:47 +0200 From: jessica.alfonsi@unipd.it Subject: [ALPS-users] restarting Lanczos iteration To: comp-phys-alps-users@lists.phys.ethz.ch Message-ID: 5b0ae17b0813c63a97720e0fbc6cc1c6.squirrel@webmail.unipd.it Content-Type: text/plain;charset=utf-8
Hi all, I'd like to modify the Lanczos *.cpp examples in IETL example folder to
be
able to restart the iteration from any interruption point during the Lanczos iteration. I suppose first one has to dump some information, for instance the cofficients of T-matrix and the starting vector, however the more difficult part would be the resuming of the iteration. Can somebody give me some hints on how accomplishing this task? Thanks in advance...
Best regards,
Jessica Alfonsi
Message: 2 Date: Fri, 22 Jul 2011 13:03:23 +0200 From: zhian asadzadeh zhian.asadzadeh@gmail.com Subject: [ALPS-users] Quantum Monte Carlo for Ising in transvers field To: comp-phys-alps-users@lists.phys.ethz.ch Message-ID: <
CAEw6G6vLtP2G8kviZ97cxgZy9Dv1x_MqyUzFWs9ejnM8WvwnmA@mail.gmail.com
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Dear All,
I am trying to do QMC at finite temperature for calculating the magnetization of *Ising model in transverse field*, but I realized just looper code is working for this model, ( the others codes doesn't work
with
off diagonal matrix elements) but the result are not so good. I am interested to modify dirloop_sse for this model, is it possible? I appreciate your help, Thanks, zhian.
On Jul 24, 2011, at 4:48 AM, zhian asadzadeh wrote:
Dear Matthias,
by \Sigma_{i,j}, I mean \sum_{i,j},
for the exact result, we know the model is integrable, so by fermionization and finally diagonalizing the Hamiltonian we will end up to an Hamiltonian with sum over independent modes, H=\sum_{k} E(k) (2 a_{k}^{dagger} a_{k}-1)
for the T=0 ground state energy, I have compared with DMRG results which are exactly same, so I am sure up to this point the form of E(k) and my summation over k space is correct.
so finally for E(T) simply we have: E(T)=\sum_{k} E(k)(2*n(k,T)-1) in which n(k,T)=1/(exp(E(k)/T)+1) ::with Boltzmann constant=1
Are you sure that you use the same units for temperature, etc. As the looper code is exact I wonder where the problem is. Can you please repeat this for a small system, e.g. 8 spins, where we can use fulldiag to compare. Also, which boundary conditions did you choose? DId you do the DMRG with periodic boundary conditions?
Matthias
Hello everyone,
I wanted to calculate the value $<S_j^z S_{j+r}^z> for a classical Heisenberg-like model as a function of $r$.
I thought typing
MEASURE_CORRELATIONS[Sz]=Sz
in the parameter-file, the usual conversion (paramert2xml filename) and running by spinmc --write filename.xml would be sufficient to get the job done, but somehow the output-file does only contain the default measurements.
Any help would be highly appreciated
All the best,
Alex
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