Ionisation feedback in star formation simulations: The role of diffuse
  fields
  We compare the three-dimensional gas temperature distributions obtained by a
dedicated radiative transfer and photoionisation code, MOCASSIN, against those
obtained by the recently-developed Smooth Particle Hydrodynamics (SPH) plus
ionisation code iVINE for snapshots of an hydrodynamical simulation of a
turbulent interstellar medium (ISM) irradiated by a nearby O star. Our tests
demonstrate that the global ionisation properties of the region are correctly
reproduced by iVINE, hence validating further application of this code to the
study of feedback in star forming regions. However we highlight potentially
important discrepancies in the detailed temperature distribution. In particular
we show that in the case of highly inhomogenous density distributions the
commonly employed on-the-spot (OTS) approximation yields unrealistically sharp
shadow regions which can affect the dynamical evolution of the system. We
implement a simple strategy to include the effects of the diffuse field in
future calculations, which makes use of physically motivated temperature
calibrations of the diffuse-field dominated regions and can be readily applied
to similar codes. We find that while the global qualitative behaviour of the
system is captured by simulations with the OTS approximation, the inclusion of
the diffuse field in iVINE (called DiVINE) results in a stronger confinement of
the cold gas, leading to denser and less coherent structures. This in turn
leads to earlier triggering of star formation. We confirm that turbulence is
being driven in simulations that include the diffuse field, but the efficiency
is slightly lower than in simulations that use the OTS approximation.
