Question about the gradient of positions

[smiles724]

Hi, great work, and thanks for sharing the code. I have a small question regarding the gradient of inputs["R"].
As far as I know, inputs["R"] represents the positions of atoms. Why do you make its requires_grad True?

        if not self.direct_forces:
            inputs["R"].requires_grad = True

[gasteigerjo]

If we don't predict forces directly (self.direct_forces=False), we calculate them via F = -dE/dx. This thus requires exactly the positions' gradients.