PM3 semi-empirical calculations have been used to model the primary di
amond nucleation in the graphite-like initial carbon layer usually pro
duced on substrates other than diamond. The effect of quenched-in dens
ity increase was simulated by compressing the graphitic environment (r
epresented by a small graphite cluster with cyclic boundary conditions
) of a carbon atom with an additional methyl group in its vicinity. Th
e critical (linear) compression for the ''sp(2)-->sp(3) phase transfor
mation'' of the fourfold coordinated carbon was estimated to be 3%.