  We propose a method to obtain adiabatic internuclear potentials via energy
variation with the intercluster-distance constraint. The adiabatic $^{16}$O +
$^{16,18}$O potentials obtained by the proposed method are applied to
investigate the effects of valence neutrons in $^{16}$O + $^{18}$O sub-barrier
fusions. Sub-barrier fusion cross sections of $^{16}$O + $^{18}$O are enhanced
more compared to those of $^{16}$O + $^{16}$O because of distortion of valence
neutrons in $^{18}$O.

Nuclear Theory;Nuclear Experiment