PRECONDITIONER

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This specifies the type of preconditioner to use in the selected diagonalization method. The valid options are: DAVIDSON which approximates the Hamiltonian matrix by the diagonal elements; H0BLOCK_INV which uses an exact Hamiltonian of H0_BLOCKSIZE and explicitly inverts it; GEN_DAVIDSON which does a spectral decomposition of H0BLOCK; ITER_INV using an iterative approach to obtain the correction vector of H0BLOCK. The H0BLOCK_INV, GEN_DAVIDSON, and ITER_INV approaches are all formally equivalent but the ITER_INV is less computationally expensive. Default is DAVIDSON.

• Type: string
• Possible Values: LANCZOS, DAVIDSON, GEN_DAVIDSON, H0BLOCK, H0BLOCK_INV, ITER_INV, H0BLOCK_COUPLING, EVANGELISTI
• Default: DAVIDSON