  To explain the observed population of supermassive black holes at z~7, very
massive seed black holes or, alternatively, super-Eddington scenarios are
needed to reach final masses of the order of 10^9 solar masses. A popular
explanation for massive seeds has been the direct collapse model, which
predicts the formation of a single massive object due to the direct collapse of
a massive gas cloud. Simulations over the last years have however shown that
such a scenario is very difficult to achieve. A realistic model of black hole
formation should therefore take fragmentation into account, and consider the
interaction between stellar-dynamical and gas-dynamical processes. We present
here numerical simulations pursued with the AMUSE code, employing an
approximate treatment of the gas. Based on these simulations, we show that very
massive black holes of 10^4-10^5 solar masses may form depending on the gas
supply and the accretion onto the protostars.
