# KrylovSelfEnergy¶

class KrylovSelfEnergy(save_self_energies=None, lambda_min=None, sparse_threshold=None, storage_strategy=None)

Self-energy calculator based on the Krylov method. The Krylov scheme uses an iterative approach for getting a subset of all the electrode modes.

Parameters: storage_strategy (SaveInMemory | StoreOnDisk | NoStorage) – The way self energies are stored between iterations. Default: SaveInMemory() lambda_min (float > 0) – The smallest logarithmic decrement of a mode to take into account. Default: 0.1 sparse_threshold (float > 0) – Self energies (in Hartree) smaller than this value treated as 0 when storing as sparse matrix. Default: 1e-12 save_self_energies – Deprecated since version 2017.0: Use storage_strategy instead.
lambdaMin()
Returns: The smallest logarithmic decrement of a mode float
saveSelfEnergies()

Deprecated since version 2017.0.

sparseThreshold()
Returns: Values treated as 0. float
storageStrategy()
Returns: The way self energies are stored between iterations. SaveInMemory | StoreOnDisk | NoStorage

## Usage Examples¶

Define that the self energy on the real contour is calculated with the Krylov method. Only modes with a decay slower than 0.05 are included.

device_algorithm_parameters = DeviceAlgorithmParameters(
self_energy_calculator_real=KrylovSelfEnergy(lambda_min=0.05),
)


Examples on how to use the storage_strategy parameter can be found in the Usage Examples of RecursionSelfEnergy.

## Notes¶

KrylovSelfEnergy uses the iterative Krylov subspace method by H. H. Sørensen et. al. [qSrensenHP+08], [qSrensenHP+09] for calculating the self energy matrix. The lambda_min parameter determines the size of the Krylov subspace. In the limit lambda_min goes to zero, the full space will be included.

## References¶

 [qSrensenHP+08] H. H. B. Sørensen, P. C. Hansen, D. E. Petersen, S. Skelboe, and K. Stokbro. Krylov subspace method for evaluating the self-energy matrices in electron transport calculations. Phys. Rev. B, 77:155301, Apr 2008. doi:10.1103/PhysRevB.77.155301.
 [qSrensenHP+09] H. H. B. Sørensen, P. C. Hansen, D. E. Petersen, S. Skelboe, and K. Stokbro. Efficient wave-function matching approach for quantum transport calculations. Phys. Rev. B, 79:205322, May 2009. doi:10.1103/PhysRevB.79.205322.