How is rotational averaging calculated in this program?

When calculating the 2D spectroscopy results using "Exciton Dynamics Lab for Light-Harvesting Complexes (GPU-HEOM) " I notice that rotational averaging is dealt with my calculating results over 4 different runs. Is this an exact averaging or an approximation? Also is there any literature you can point me towards which explains how this works? When I have looked at this problem I have found I require 21 different runs, but I was assuming a general configuration for the polarisations of the beams.

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Tobias Kramer@ onFrom the supporting information document (tab supporting doc): "An approximation to full rotational averaging is available by selecting one of four polarisation directions of the laser beam and adding up all the resulting spectra (this corresponds to an octahedral approximation of the sphere). Due to runtime limitations the icosahedral averaging mode is not available at this time."

This corresponds to an average over molecular complexes with random orientations by rather than rotating the molecule to consider different orientations of the laser field. The solid-angle integration is effectively approximated by summing over faces of platonic polyhedra (in the nanohub version an octahedron)

See also B. Hein, C. Kreisbeck, T. Kramer, and M. Rodriguez, New J. Phys. 14, 023018 (2012) [open access], section about 2d-spectra.

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