I found a link on this board to a Youtube video describing how to overcome convergence problems for high-spin systems using Q-Chem. I thank whoever made this video since it has helped me solve some difficult problems. However, there is an aspect to the explanation I do not understand and request clarification on. The video in question is this one: https://www.youtube.com/watch?v=ntJN3O_-tJc&feature=channel

At 5:15, the video provides an example of how to obtain a solution for the high-spin tridehydrobenzene triradical using a three-step calculation. Around 6:50, an explanation is given for using the "occupied" keyword to rearrange the orbitals. It is stated that orbital 17 is one of the radical orbitals from "a previous calculation", and it will be rearranged to ensure that it remains virtual for the final step. My question is, where does this knowledge that orbital 17 is one of the singly occupied orbitals come from? If this rearrangement is required to ensure convergence with the correct occupancies, does one need a priori knowledge of the orbital occupancies? If so, where does it come from in the absence of a correctly converged calculation?

And one last very basic question, where in the Q-Chem output is the orbital occupancy found? The orbital energies are readily determined from the output, but I do not see a field where the occupancy is provided.

Any help that can be provided is greatly appreciated.
« Last edit by kylijoki on Sat May 21, 2016 9:41 pm. »