Questions about the asperity interaction between Fe and Al

Hi,dear all:

I have constructed a atomic asperity junction between Al and Fe.
However, a repulsive force occurs before the jump to contact happened (Please see the attached figures).
This is quite different with the phenomena from some relevant literature
(Chen P, Shen Y. Nanocontact between BCC tungsten and FCC nickel using the quasicontinuum method[J]. International Journal of Solids and Structures, 2008, 45(24): 6001-6017.),
in which there is no repulsive forces before the attraction happens.
Moreover, there has been very litter research on the nanocontact between BCC Fe and FCC Al both experimentally and numerically.
I would like to ask: is this consistent with the real physical phenomena?
Kind regards
Tsung Fong

What are you using for the potential between Fe and Al atoms?