What is the unit of free energy gradient with respect to dynamical matrix?

[gooaah]

Hi, I want to compare the gradient of free energy computed by DFT and MLP. I got the gradient with respect to dyn matrix by the function get_preconditioned_gradient. But I am not sure what the unit it is.

[mesonepigreco]

It is in Rydberg atomic units.
It depends on root representation and preconditioning.
By default (preconditioned, normal representation) it has the same units as the force constants matrix (i.e. Ry/Bohr^2).

[gooaah]

Great thanks Lorenzo!
Now I compute the gradient without preconditioning and with normal representation. In this case, is the unit Bohr^2?
In addition, if I want to compare DFT and MLP results, which type of dyn gradient makes more sense? The one with or without preconditioning?