I am trying to calculate the ground state energy of the transverse Ising-Model ( -J*Sx(i)*Sx(j)-h*Sz(i) ) on a simple 1d-chain-lattice with the DMRG and DIRLOOP applications. The results seems to be calculated with a constrained basis even without the CONSERVED_QUANTUMNUMBERS="Sz" parameter (compared to the FULLDIAG where the parameter has its effect on the results). It looks more like the half of a XY-model. So my question is if there is a special problem with the DMRG and DIRLOOP applications and the Ising-Model.
Btw, wenn changing the x- and z-axis then the LOOP application gets the same results as the FULLDIAG, but DIRLOOP aborts with an 'Did not find raising and lowering operators' error.
best regards,
Armin
Yes, the SSE code cannot do any transverse field at this time, but I thought it should give an error message instead. The result 'Did not find raising and lowering operators' is such an error message for that formulation, but there should be a similar one for the other case as well. I will check into this.
Matthias
On 25 Jun 2007, at 14:23, Armin wrote:
I am trying to calculate the ground state energy of the transverse Ising-Model ( -J*Sx(i)*Sx(j)-h*Sz(i) ) on a simple 1d-chain-lattice with the DMRG and DIRLOOP applications. The results seems to be calculated with a constrained basis even without the CONSERVED_QUANTUMNUMBERS="Sz" parameter (compared to the FULLDIAG where the parameter has its effect on the results). It looks more like the half of a XY-model. So my question is if there is a special problem with the DMRG and DIRLOOP applications and the Ising-Model.
Btw, wenn changing the x- and z-axis then the LOOP application gets the same results as the FULLDIAG, but DIRLOOP aborts with an 'Did not find raising and lowering operators' error.
best regards,
Armin
Thank you for your answers. I can break down the problem to the case with no external field:
LATTICE="chain lattice" MODEL="spin" but with only this bondterm: -J*Sx(i)*Sx(j) h=Gamma=D=0 L=6,J=1
dmrg: SWEEPS=4,MAXSTATES=128 dirloop: THERMALIZATION=2000,SWEEPS=20000, EPSILON=0.2,T=0.01
The results for the ground state energy are: Fulldiag: -1.5 Dirloop: -1.0 Dmrg: -1.28
with CONSERVED_QUANTUMNUMBERS=Sz: Fulldiag: -1.0 Dirloop: -1.0 Dmrg: -1.28
and with -J*Sz(i)*Sz(j): Fulldiag: -1.5
I think there is no superposition of bases with Sz_total!=0 in the constraint case.
thanks in advance Armin
On 12 Jul 2007, at 13:09, Armin Sauter wrote:
Thank you for your answers. I can break down the problem to the case with no external field:
LATTICE="chain lattice" MODEL="spin" but with only this bondterm: -J*Sx(i)*Sx(j) h=Gamma=D=0 L=6,J=1
dmrg: SWEEPS=4,MAXSTATES=128 dirloop: THERMALIZATION=2000,SWEEPS=20000, EPSILON=0.2,T=0.01
Dirloop should not work on that model. I'll check this. Did you not get an error message?
The results for the ground state energy are: Fulldiag: -1.5 Dirloop: -1.0 Dmrg: -1.28
with CONSERVED_QUANTUMNUMBERS=Sz: Fulldiag: -1.0 Dirloop: -1.0 Dmrg: -1.28
and with -J*Sz(i)*Sz(j): Fulldiag: -1.5
I think there is no superposition of bases with Sz_total!=0 in the constraint case.
You should never set CONSERVED_QUANTUMNUMBERS=Sz for models that do not conserve Sz, such as your model.
To reproduce the problem and fix it, could you please send us your input files (parameter, models)
Matthias
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