DMRG Options

me->dot

  • Values: 1 or 2.

  • Meaning: Select 2-site or 1-site algorithm, unless affected by last_site_1site.

decomp_last_site

  • Meaning: If false, decomposition for affected sites will be skipped.

  • Default: true.

  • Affected sites: - For me->dot = 1, only affect site n - 1 for forward and site 0 for backward sweep. - For me->dot = 2 and last_site_1site = true, only affect site n - 1 for forward sweep.

  • Side effect: some sites will have a canonical form different from the typical one.

  • Restriction: Only active for me->dot = 1 (or when me->dot = 2 but last_site_1site = true).

  • Accuracy: Should not affect accuracy.

  • Efficiency: decomp_last_site = false provides faster speed.

  • Indicator: When decomp_last_site = false, the affected site will print Mmps = 0.

last_site_svd

  • Meaning: If true, for affected sites: - Davidson step will be skipped - and decomposition method will be changed to SVD - and if noise_type = DensityMatrix, it will be changed to Wavefunction.

  • Default: false.

  • Affected sites: only affect site n - 1 for backward sweep.

  • Restriction: Only active for me->dot = 1 (or when me->dot = 2 but last_site_1site = true).

  • Accuracy: If true: - Skipping davidson step should not affect accuracy. - Using SVD instead of density matrix may decrease accuracy.

  • Efficiency: last_site_svd = true provides faster speed.

  • Indicator: When last_site_svd = true, the affected site will print Ndav = 0 E = 0.0.

  • Requirement: Need DMRGSCI.

last_site_1site

  • Meaning: If true, for affected sites: - In forward sweep, 2-site iteration for sites n - 2 and n - 1 will be changed to 1-site iteration for site n - 1. - In backward sweep, 2-site iteration for sites n - 2 and n - 1 will be changed to 1-site iteration for site n - 1.

  • Default: false.

  • Affected sites: only affect site n - 2 and n - 1 for forward and backward sweep.

  • Side effect: MPS bond between site n - 2 and site n - 1 will not be updated in forward sweep.

  • Restriction: Only active for me->dot = 2.

  • Accuracy: If true: - Accuracy decreased because of 1-site algorithm. - Accuracy decreased because of the side effect.

  • Efficiency: last_site_1site = true provides faster speed.

  • Indicator: When last_site_1site = true, the affected site will print Site = <n - 1> LAST.

  • Requirement: Need DMRGSCI.

Early DMRG stop

To stop a DMRG run gracefully, e.g., in case of non-convergence, create a file named BLOCK_STOP_CALCULATION with the text STOP. The DMRG run will then stop as it would be converged after the current sweep is over.