The existance of an initial conditions subsection in the output section of the configuration file enables the IC output. In addition, all particles that cross the hypersurface of predefined proper time are removed from the evolution. This proper time is taken from the Proper_Time field in the Initial_Conditions subsection when configuring the output. If this information is not provided, the default proper time corresponds to the passing time of the two nuclei, where all primary interactions are expected to have occured:

\[ \tau_0 = (r_\mathrm{p} \ + \ r_\mathrm{t}) \ \left(\left(\frac{\sqrt{s_\mathrm{NN}}} {2 \ m_\mathrm{N}}\right)^2 - 1\right)^{-1/2} \]

Therein, \( r_\mathrm{p} \) and \( r_\mathrm{t} \) denote the radii of the projectile and target nucleus, respectively, \( \sqrt{s_\mathrm{NN}}\) is the collision energy per nucleon and \( m_\mathrm{N} \) the nucleon mass. Note though that, if the passing time is smaller than 0.5 fm, the default porper time of the hypersurface is taken to be \(\tau = 0.5 \) as a minimum bound to ensure the proper time is large enough to also extract reasonable initial conditions at RHIC/LHC energies. If desired, this lowest possible value can also be specifie in the configuration file in the Lower_Bound field.
Once initial conditions are enabled, the output file named SMASH_IC (followed by the appropriate suffix) is generated when SMASH is executed.
The output is available in Oscar1999, Oscar2013, binary and ROOT format, as well as in an aditional ASCII format (see ASCII IC Output). The latter is meant to directly serve as an input for the vHLLE hydrodynamics code (I. Karpenko, P. Huovinen, M. Bleicher: Comput. Phys. Commun. 185, 3016 (2014)).

Oscar output

In case of the Oscar1999 and Oscar2013 format, the structure is identical to the Oscar Particles Format (see OSCAR Particles Format).
In contrast to the usual particles output however, the initial conditions output provides a list of all particles removed from the evolution at the time when crossing the hypersurface. This implies that neither the initial particle list nor the particle list at each time step is printed.
The general Oscar structure as described in OSCAR Particles Format is preserved.

Binary output

The binary initial conditions output also provides a list of all particles removed from the evolution at the time when crossing the hypersurface. For each removed particle a 'p' block is created stores the particle data. The general binary output structure as described in Binary Format is preserved.

ROOT output

The initial conditions output in shape of a list of all particles removed from the SMASH evolution when crossing the hypersurface is also available in ROOT format. Neither the initial nor the final particle lists are printed, but the general structure for particle TTrees, as described in ROOT Format, is preserved.