The density-matrix overlap

Is it a way to request PSI4 to calculate the density-matrix overlap?

Please see equation (9) in

Thank you!

Not directly. The SNS-MP2 plugin code can be found here:

All quantities should be found inside.

It looks like the equation reduces to Tr(Ga*S*Gb*S) where S is the overlap matrix and Ga and Gb are the AO density matrices, so the metric should be really simple to calculate.