velocity¶
-
sisl.physics.electron.
velocity
(state, dHk, energy=None, dSk=None, degenerate=None)[source]¶ Calculate the velocity of a set of states
These are calculated using the analytic expression (\(\alpha\) corresponding to the Cartesian directions):
\[\mathbf{v}_{i\alpha} = \frac1\hbar \langle \psi_i | \frac{\partial}{\partial\mathbf k}_\alpha \mathbf H(\mathbf k) | \psi_i \rangle\]In case of non-orthogonal basis the equations substitutes \(\mathbf H(\mathbf k)\) by \(\mathbf H(\mathbf k) - \epsilon_i\mathbf S(\mathbf k)\).
The velocities calculated are without the Berry curvature contributions.
- Parameters
state (array_like) – vectors describing the electronic states, 2nd dimension contains the states. In case of degenerate states the vectors may be rotated upon return.
dHk (list of array_like) – Hamiltonian derivative with respect to \(\mathbf k\). This needs to be a tuple or list of the Hamiltonian derivative along the 3 Cartesian directions.
energy (array_like, optional) – energies of the states. Required for non-orthogonal basis together with dSk. In case of degenerate states the eigenvalues of the states will be averaged in the degenerate sub-space.
dSk (list of array_like, optional) – \(\delta \mathbf S_k\) matrix required for non-orthogonal basis. This and energy must both be provided in a non-orthogonal basis (otherwise the results will be wrong). Same derivative as dHk
degenerate (list of array_like, optional) – a list containing the indices of degenerate states. In that case a prior diagonalization is required to decouple them. This is done 3 times along each of the Cartesian directions.
- Returns
velocities per state with final dimension
(state.shape[0], 3)
, the velocity unit is Ang/ps. Units may change in future releases.- Return type