  The expulsion of the unconverted gas at the end of the star formation process
potentially leads to the expansion of the just formed stellar cluster and
membership loss. The degree of expansion and mass loss depends largely on the
star formation efficiency and scales with the mass and size of the stellar
group as long as stellar interactions can be neglected. We investigate under
which circumstances stellar interactions between cluster members become so
important that the fraction of bound stars after gas expulsion is significantly
altered. The Nbody6 code is used to simulate the cluster dynamics after gas
expulsion for different SFEs. Concentrating on the most massive clusters
observed in the Milky Way, we test to what extend the results depend on the
model, i.e. stellar mass distribution, stellar density profile etc., and the
cluster parameters, such as cluster density and size.We find that stellar
interactions are responsible for up to 20% mass loss in the most compact
massive clusters in the Milky Way, making ejections the prime mass loss process
in such systems. Even in the loosely bound OB associations stellar interactions
are responsible for at least ~5% mass loss. The main reason why the importance
of encounters for massive clusters has been largely overlooked is the often
used approach of a single-mass representation instead of a realistic
distribution for the stellar masses. The density-dependence of the
encounter-induced mass loss is shallower than expected because of the
increasing importance of few-body interactions in dense clusters compared to
sparse clusters where 2-body encounters dominate.
