  We present a new simulation setup using the MURaM radiative
Magnetohydrodynamic (MHD) code that allows to study the formation of
collisional polarity inversion lines (cPILs) in the photosphere and the coronal
response including flares. In this scheme we start with a bipolar sunspot
configuration and set the spots on collision course by imposing the appropriate
velocity field at the footpoints in the subphotospheric boundary. We produce
different setups with the same initial spot separation by varying physical
parameters such as the collision speed and minimum collision distance. While
all setups lead to the formation of an EUV and X-ray sigmoid structure, only
the cases with a close passing of the spots cause flares and mass eruptions.
The energy release is in the $1-2 \times 10^{31}$ erg range, putting the
simulated flares into the upper C-class to lower M-class range of GOES X-ray
1-8 A flux. While the setup with the more distant passing of the spots does not
lead to a flare, the corona is nonetheless substantially heated, suggesting
non-eruptive energy release mechanisms. We focus our discussion on two
particular setups that differ in spot coherence and resulting cPIL length
persistence. We find different timings in the transition from a sheared
magnetic arcade (SMA) to magnetic flux rope (MFR); the setup with a large
length but shorter duration cPIL produces a MFR during the eruption, while the
MFR is pre-existing in the setup with a large length and longer duration cPIL.
While both result in flares of comparable strength and the eruption of a CME,
the setup with pre-existing MFR (and embedded filament) leads to an MFR
eruption with a larger mass content.
