- Comp-phys-alps-users - lists.phys.ethz.ch

Re: [ALPS-users] Expectation value
by Matthias Troyer 14 Jan '09

14 Jan '09

Sy-reflection is a symmetry, and thus there is always the y-reflected state as well which has the same energy. For the Sy-Sy correlations you can just measure S+ - S+, S+ - S- and S- - S- correlations and calculate it from the, without the need for complex arithmetic Matthias On Jan 14, 2009, at 12:56 PM, zhian asadzadeh wrote: > Dear > I don't think so, when we increase the field this is true. and for > tow point correlations <Sy Sy>, I need to define Sy. > Thanks > Zhian > > On Thu, Jan 15, 2009 at 12:20 AM, Matthias Troyer > <troyer(a)phys.ethz.ch> wrote: > Then <Sy> should be 0 by symmetry > > > On Jan 14, 2009, at 12:48 PM, zhian asadzadeh wrote: > >> Hi >> I have an isotropy in Z direction, and the field is in X direction >> Thanks >> Zhian >> >> On Thu, Jan 15, 2009 at 12:15 AM, Matthias Troyer <troyer(a)phys.ethz.ch >> > wrote: >> Is the transverse field in the x or y direction? >> >> >> On Jan 14, 2009, at 12:43 PM, zhian asadzadeh wrote: >> >>> Hi >>> >>> My model doesn't conserve U(1) symmetry. My model is spin chain >>> in transverse magnetic field. if we want to define the Sy we must >>> use complex number i, so can we define complex number in Model.XML >>> file? >>> >>> Thanks, >>> Zhian >>> >>> On Wed, Jan 14, 2009 at 9:54 PM, Matthias Troyer <troyer(a)phys.ethz.ch >>> > wrote: >>> Does your model conserve SU(2) or U(1) symmetry? In that case the >>> expectation value is 0. Otherwise you should be able to measure it >>> >>> Matthias >>> >>> >>> On 30 Dec 2008, at 04:33, zhian asadzadeh wrote: >>> >>> Hi Dears >>> >>> Can i measure the expectation value of the y component of Spin >>> operator (Sy)?( in DMRG ) >>> >>> Thanks >>> >>> Zhian >>> >>> >> >> > >

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Re: [ALPS-users] Expectation value
by Matthias Troyer 14 Jan '09

14 Jan '09

Then <Sy> should be 0 by symmetry On Jan 14, 2009, at 12:48 PM, zhian asadzadeh wrote: > Hi > I have an isotropy in Z direction, and the field is in X direction > Thanks > Zhian > > On Thu, Jan 15, 2009 at 12:15 AM, Matthias Troyer > <troyer(a)phys.ethz.ch> wrote: > Is the transverse field in the x or y direction? > > > On Jan 14, 2009, at 12:43 PM, zhian asadzadeh wrote: > >> Hi >> >> My model doesn't conserve U(1) symmetry. My model is spin chain in >> transverse magnetic field. if we want to define the Sy we must use >> complex number i, so can we define complex number in Model.XML file? >> >> Thanks, >> Zhian >> >> On Wed, Jan 14, 2009 at 9:54 PM, Matthias Troyer >> <troyer(a)phys.ethz.ch> wrote: >> Does your model conserve SU(2) or U(1) symmetry? In that case the >> expectation value is 0. Otherwise you should be able to measure it >> >> Matthias >> >> >> On 30 Dec 2008, at 04:33, zhian asadzadeh wrote: >> >> Hi Dears >> >> Can i measure the expectation value of the y component of Spin >> operator (Sy)?( in DMRG ) >> >> Thanks >> >> Zhian >> >> > >

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Re: [ALPS-users] Expectation value
by Matthias Troyer 14 Jan '09

14 Jan '09

Is the transverse field in the x or y direction? On Jan 14, 2009, at 12:43 PM, zhian asadzadeh wrote: > Hi > > My model doesn't conserve U(1) symmetry. My model is spin chain in > transverse magnetic field. if we want to define the Sy we must use > complex number i, so can we define complex number in Model.XML file? > > Thanks, > Zhian > > On Wed, Jan 14, 2009 at 9:54 PM, Matthias Troyer > <troyer(a)phys.ethz.ch> wrote: > Does your model conserve SU(2) or U(1) symmetry? In that case the > expectation value is 0. Otherwise you should be able to measure it > > Matthias > > > On 30 Dec 2008, at 04:33, zhian asadzadeh wrote: > > Hi Dears > > Can i measure the expectation value of the y component of Spin > operator (Sy)?( in DMRG ) > > Thanks > > Zhian > >

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error in instaling alps
by Huan Tran 14 Jan '09

14 Jan '09

Dear all, I am reinstall alps-1.3.3 on my new Ubuntu. During the installation of alps-applications-1.3.3, I got the following message: spinmc_factory.C: In constructor ?AbstractSpinSim<MAT>::AbstractSpinSim(const alps::ProcessList&, const alps::Parameters&, int) [with MAT = DiagMatrix<double, 3>]?: spinmc_factory.C:194: internal compiler error: Segmentation fault Please submit a full bug report, with preprocessed source if appropriate. See <file:///usr/share/doc/gcc-4.3/README.Bugs> for instructions. make[2]: *** [spinmc_factory.o] Error 1 make[2]: Leaving directory `/usr/local/src/alps-applications-1.3.3/mc/spins' make[1]: *** [install-recursive] Error 1 make[1]: Leaving directory `/usr/local/src/alps-applications-1.3.3/mc' make: *** [install-recursive] Error 1 I guess that this comes from boost library. Although I have tried many version, from 1.33.1 to 1.37.0, it does not work. Searching on the web does help, too. Could anybody have a hint for me? Thanks Huan Tran ----------------------------------------------------------------

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"fermionic" quantum numbers
by Cezary Sliwa 09 Jan '09

09 Jan '09

Hello, From http://alps.comp-phys.org/mediawiki-1.9.3/index.php/Tutorials:ModelHOWTO "Optionally, a type attribute can be set to bosonic (the default) or fermionic. It should be set to fermionic when the quantum number is a fermionic number operator. This information will be used when determining commutation relation between operators on different sites." This is very imprecise. To be honest, I do not understand that at all. First of all, good quantum numbers take numerical values, and numbers commute. Hence, the relations for quantum numbers are always *commutation* relations. The anticommutation relations are for the creation and annihilation *operators*. Hence, whether or not it make sense to assign such a "type=" attribute to a degree of freedom (call it a QUANTUMNUMBER), the attribute applies to *operators*! Moreover, not all operators, but only those that are odd in the creation and annihilation operators. For example, the spin operator for a pair of spin-up, spin-down fermion states satisfies *commutation* relations. Now please tell me why the code refuses to generate a matrix (probably for the hopping and exchange terms, but the error message does not state which terms pose a problem). Both terms are even in the creation and annihilation operators (capital S refers to a bosonic spin): <SITEBASIS name="orbital"> <QUANTUMNUMBER name="Nup" min="0" max="1" type="fermionic"/> <QUANTUMNUMBER name="Ndown" min="0" max="1" type="fermionic"/> <OPERATOR name="a_up" matrixelement="1"> <CHANGE quantumnumber="Nup" change="-1"/> </OPERATOR> <OPERATOR name="adag_up" matrixelement="1"> <CHANGE quantumnumber="Nup" change="1"/> </OPERATOR> <OPERATOR name="a_down" matrixelement="1"> <CHANGE quantumnumber="Ndown" change="-1"/> </OPERATOR> <OPERATOR name="adag_down" matrixelement="1"> <CHANGE quantumnumber="Ndown" change="1"/> </OPERATOR> <OPERATOR name="splus" matrixelement="1/2"> <CHANGE quantumnumber="Nup" change="1"/> <CHANGE quantumnumber="Ndown" change="-1"/> </OPERATOR> <OPERATOR name="sminus" matrixelement="1/2"> <CHANGE quantumnumber="Nup" change="-1"/> <CHANGE quantumnumber="Ndown" change="1"/> </OPERATOR> <OPERATOR name="sz" matrixelement="(Nup-Ndown)/2"/> <OPERATOR name="n" matrixelement="Nup+Ndown"/> </SITEBASIS> <BONDOPERATOR name="exchange_xy" source="x" target="y"> 1/2*(splus(x)*Sminus(y)+sminus(x)*Splus(y)) </BONDOPERATOR> <BONDOPERATOR name="exchange_z" source="x" target="y"> sz(x)*Sz(y) </BONDOPERATOR> <BONDOPERATOR name="hop" source="x" target="y"> adag_up(x)*a_up(y)+adag_up(y)*a_up(x)+adag_down(x)*a_down(y)+adag_down(y)*a_down(x) </BONDOPERATOR> Regards, Cezary Sliwa

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Quantum heisenberg rectangular anti-fm lattice with random holes
by Brian Keith 08 Jan '09

08 Jan '09

I am endeavoring to create a rectangular QHAF lattice that has some of the magnetic sites "missing". Does anyone have any advice on how to go about creating a model that includes this randomness, these random, exchangeless holes in the lattice? thanks in advance, Brian

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Magnetization for transverse Ising model
by Norbert Schuch 02 Jan '09

02 Jan '09

Hi, I am trying to compute the magnetization for the transverse field Ising model in 3D. If I understand correctly, I have to use Looper and place the field along X and the coupling along Z, i.e. what I do is LATTICE="simple cubic lattice" MODEL="spin" L=8 Jz=1 Jxy=0 T=0.1 THERMALIZATION=1000 SWEEPS=10000 REPRESENTATION="SSE" {Gamma=0;} {Gamma=1;} etc. The simulation works, however the magnetization is zero -- I assume this is because this is the magnetization in Z direction. What do I have to do in order to compute the magnetization along the transverse field? Thanks a lot, Norbert

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Re: [ALPS-users] hamiltonian matrix
by Matthias Troyer 29 Dec '08

29 Dec '08

Look at the example/model directory in the ALPS libraries source trees. This is a program which prints the matrix for a model you specify. If you edit the file matrix.h you can also print all the states which gives you the matrix. Please be aware though that the ALPS exact diagonalization codes cannot do the biggest systems that you might be able to do using a matrix-free specialized code. What will you want to do after you checked your Mathematica code? Matthias On Dec 27, 2008, at 6:58 PM, khalid hassan wrote: > No I am using it for small systems. actually i made a code in > mathematica that calculates the hamiltonian matrix and basis > vectors, but it cannot be guaranteed 100% as i may have some > situations not obliged. Now my professor wants to check my code with > alps and then switch to alps. I dont know what next. for having the > matrix from the code I need to know the c++, for which i have to > spend some time as i know a little bit of c++ already. I want to > know that if I am on the right track. as I may spend 3 months on > learning c++ then i know that its not possible in alps. I am > thinking what freedom it will give me for calculating any > hamiltonian for any system. you said as it is possible now i can do > it with confidence. as my professor has given me this task, as i am > new in this field i dont know the reason. > > If you have some suggestion for me to have this without needing to > learn all c++ it will save my time as I am paying myself for my phd > program. > > Thanks to you for your answer. > > Best Regards > > Loane > > > --- On Sat, 12/27/08, Matthias Troyer <troyer(a)phys.ethz.ch> wrote: > >> From: Matthias Troyer <troyer(a)phys.ethz.ch> >> Subject: Re: [ALPS-users] hamiltonian matrix >> To: mkhloane(a)yahoo.com, comp-phys-alps-users(a)phys.ethz.ch >> Date: Saturday, December 27, 2008, 12:26 PM >> Look at the sparsediag or fulldiag code. You can print the >> basis and the matrix elements, but be warned that this can >> be a HUGE matrix. Why do you want to print it? >> >> Matthias >> >> On Dec 27, 2008, at 12:22 AM, khalid hassan wrote: >> >>> Dear all >>> >>> I am using the alps for a fermionic hubbard system. It >> gives the energies. I want the matrix elements of >> hamiltonian matrix. how can I have the hamiltonian matrix >> and basis states. >>> >>> Best Regards >>> Khalid Loane >>> >>> >>> >>> > > > > >

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hamiltonian matrix
by khalid hassan 27 Dec '08

27 Dec '08

Dear all I am using the alps for a fermionic hubbard system. It gives the energies. I want the matrix elements of hamiltonian matrix. how can I have the hamiltonian matrix and basis states. Best Regards Khalid Loane

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DMRG for Antiferromagnetic spin one half chain
by zhian asadzadeh 15 Dec '08

15 Dec '08

Hi Dears I have got following results:" for open boundary condition" SWEEP=8, MAXSTATES=400, L=200, E0= -0.44220777784 SWEEP=50, MAXSTATES=500, L=200, E0= -0.4422077778446504 SWEEP=8, MAXSTATES=150, L=600, E0= -0.442833001737 SWEEP=8, MAXSTATES= 500, L=600, E0=- 0.44283300822 SWEEP=8, MAXSTATES= 150, L=700, E0= -0.442877 We see that the result still have not got to -0.443147.maybe we increase the size ,getting to this energy but it takes a lot of time . for periodic boundary condition the energy that achieved is lower. I have a question. Are there some techniques for use of this algorithm such that, for example, for 100 or 200 sites we get to the desire energy?

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