the single d parameter is used in erose_form=2 by setting attrac=repuls=d, see also the documentation on the different forms of the Rose equation. This selection is the one implemented in Lee's KISSMD and in fact the original one proposed by Rose (1984).
So for a single element you would set in the parameter file:
erose_form = 2
attrac(1,1) = 0.05
repuls(1,1) = 0.05
Gets a bit repetitive in larger systems, but that's just the way it is.
(Side note: From my understanding, using anything other than 0.05 is highly specialized, as it diverges from the postulated UBER. Previous authors seem to disagree or we wouldn't have the options, but I never found an argument for why.)