Feature request: Descriptor gradients

[NicklasOsterbacka]

I would like to be able to access gradients of descriptors w.r.t. atomic coordinates for some prototype work I am doing with Calorine. Would it be possible to write a function for this in NEP_CPU, @brucefan1983? From what I can tell, the gradients are currently baked directly into the force expressions which makes it hard for me to see which bits would go where.

[brucefan1983]

Could you specify the exact quantity you need? Is it

$$ \frac{\partial q_{\nu}^i} {\partial \vec{r}_{ij}} $$

for all the atoms $i$ and all the neighbors $j$, and all the descriptor component $\nu$?

I am also curious what will be the usage.

[NicklasOsterbacka]

Yes, those should be the quantities I would like to access!

I have sent you an email with the details. Hope that's alright!