tightbinder.observables.restricted_density_matrix#

restricted_density_matrix(system, partition, nmoments=100, npoints=200, nmoments_dos=300, r=10)[source]#

Routine to compute the one-particle density matrix, restricted to one spatial partition of the system. First it estimates the Fermi energy from the DOS computed with the KPM, and then uses it to compute the reduced density matrix.

Parameters:

  • system (System) – System whose reduced density matrix we want to compute.

  • partition (list) – List of indices of atoms where the reduced density matrix is computed.

  • nmoments (int) – Number of moments in the KPM expansion. Defaults to 100.

  • npoints (int) – Number of used to sample the density of states. Defaults to 200.

  • nmoments_dos (int) – Number of moments in the KPM expansion of the DoS. Defaults to 300.

  • r (int) – Number of samples in the stochastic evaluation of the trace. Defaults to 10.

Return type:

ndarray

Returns:

Reduced density matrix.