A little help with a two particle Hamiltonian

[LeeT]

TL;DR

A little help with a two-particle hamiltonian

Hello, I'm working on a project. I need to understand every equation in a paper.
I need to calculate the spatial derivative of G (d/dR), a two-particle Hamiltonian. However, G is a function of P- the density matrix and P is a function of R. Is it a "special derivative"?
Here is the attached paper. <Moderator's note: deleted for copyright reasons>
thank you very much,
Lee

Moderator's note: Paper can be found at:
https://doi.org/10.1063/1.3152120

 

[A. Neumaier]

the spatial derivative of G (d/dR), a two-particle Hamiltonian. However, G is a function of P- the density matrix and P is a function of R.

The derivative with respect to R of a function G which is a function of P, which is a function of R can be computed by the chain rule. Nothing ''special'' is needed.