I tried to calculate the energy barrier for different paths of Mg diffusion on the T Graphene nanosheet using DMol3. Here I added a picture in which I tried to diffuse a Mg atom from the tetragon site to the octagon site. But after 17 iterations it fails and the error message is "Unable to bracket maximum from both endpoints, please check endpoints".

why did this problem arise? and how to solve it?

# Another problem I found is when I merge two nanosheets in the reaction preview, the atom in the nanosheet has disappeared, I found no atom on it! why????