July 2009 - Comp-phys-alps-users

Problems with worms??
by Jakub Zakrzewski 27 Oct '10

27 Oct '10

Hello, Sometimes QMC worm code (used on Bose-Hubbard) terminates with the following error: here come first earlier succesful simulations then ... Created run 85 remote on Host ID: 84 Created run 86 remote on Host ID: 85 Created run 87 remote on Host ID: 86 Created run 88 remote on Host ID: 87 All processes have been assigned Checking if Simulation 1 is finished: not yet, next check in 120 seconds ( 0% done). q = -0 state1 = 0 state2 = 0 bond_type = 0 zero matrix element in remove_jump application called MPI_Abort(MPI_COMM_WORLD, -2) - process 67 Could somebody advice what I can do? Best regards Kuba

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Local Minima in DMRG
by Jesse Kinder 16 Jul '09

16 Jul '09

I was looking into the convergence of the ground state energy in DMRG as a function of NUMSTATES. For instance, on a 1D chain of spinless fermions with open boundary conditions at half-filling (L=36, N_TOTAL=12) and interaction strength V0=4, the ground state energies after 30 sweeps are M=2 E0 = -8.6661 M=4 E0 = -9.6249 M=8 E0 = -9.7115 M=100 E0 = -9.7133 The truncation error for the M=2 run was just 0.00167, so it is surprising (to me, at lest) that the energy is off by more than 10 percent. A discrepancy of 10 percent or more occurs for chains of different lengths and interaction potentials of different strengths. Doing 100 sweeps instead of 30 has no effect on the first 5 digits of the M=2 results. Nor does increasing NUM_WARMUP_STATES to 100. One possibility is that the calculation is getting stuck in a local minimum. Does the ALPS DMRG routine have any method for avoiding local minima? For instance, adding a small amount of noise to the calculation to allow tunneling out of local minima? Even if the results of the above calculations simply reflect the poor quality of the M=2 wave function, it would still be useful to know how to handle local minima that might occur in DMRG calculations. Jesse

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Green Fuction and Local Magnetization with looper
by João Manuel Viana Parente Lopes 07 Jul '09

07 Jul '09

Dear Alps list, Greatings from Angola... I am trying to extract the Green Function and the local magnetization running the loop code. I tried into the simplest example.. param file: LATTICE="open chain lattice" MODEL="spin" local_S=1/2 L=10 J=1 INITIAL_SITE=1 THERMALIZATION=15000 SWEEPS=150000 REPRESENTATION="SSE" MEASURE[Green Function]=true MEASURE[Correlations]=true MEASURE[Local Susceptibility]=true {T=0.05;} the simulation runs in 1m but there is no output for either Green's Funtion or Local Magnetization... Am I doing something terrible wrong or the looper code is not given these measures? Thanks in Advance João

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