Open-shell exchange matrix

We believe this behavior to be indicative of a calculation with open-shell character. The swapping of the HOMO positions between pairs of subsystems is actually equivalent to the exchange of electrons between these subsystems. On average, the situation probably amounts to the creation of unpaired electrons in two or more subsystems. The pseudo closed-shell density matrix formula in equation (14) is not equipped to deal with unpaired electrons, so convergence is difficult to achieve, and any results are nonphysical. 

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