Qtbm
Parameters for the quantum transmitting boundary method (QTBM).
Note
Only used in simulations where
formalism is set to "wf".
max_batch_size#
The maximum number of energies that are batched together when computing open boundary conditions (OBCs) in the QTBM solver.
This can be used to reduce the memory footprint of the QTBM solver, at the cost of increased computation time.
low_rank_obc#
Whether to use reduced rank for the boundary self-energies.
If set to True, boundary self-energies are moved to the right-hand-side of the linear system, which greatly reduces fill-in during factorization.
The system matrix becomes Hermitian or even real symmetric in gamma-only
simulations. Therefore, the low_rank_obc parameter can only be used in
combination with direct solvers that can exploit the symmetry, i.e.,
direct_solver="cudss" on GPU,
direct_solver="pardiso" on CPU, and
direct_solver="thomas" on both CPU and GPU.
Warning
Potentially the system matrix can become very ill-conditioned if an energy is too close to a Van Hove singularity. Without low rank, the OBCs regularize the system matrix.