displacement

sisl.physics.phonon.displacement(mode, hw, mass)

Calculate real-space displacements for a given mode (in units of the characteristic length)

The displacements per mode may be written as:

\[\mathbf{u}_{i\alpha} = \epsilon_{i\alpha}\sqrt{\frac{\hbar}{m_i \omega}}\]

where \(i\) is the atomic index.

Even for negative frequencies the characteristic length is calculated for use of non-equilibrium modes.

Parameters

modearray_like

vectors describing the phonon modes, 2nd dimension contains the modes. In case of degenerate modes the vectors may be rotated upon return.

hwarray_like

frequencies of the modes, for any negative frequency the returned displacement will be 0.

massarray_like

masses for the atoms (has to have length mode.shape[1] // 3

Returns

numpy.ndarray

displacements per mode with final dimension (mode.shape[0], 3), displacements are in Ang