  Numerical simulations are a crucial tool to understand the relationship
between debris discs and planetary companions. However, simulations throughout
the literature have been conducted with various initial conditions often with
little or no justification. In this paper, we aim to study the dependence on
the initial conditions of N-body simulations modelling the interaction between
a massive and eccentric planet on an exterior debris disc. To achieve this, we
first classify three broad approaches used in the literature and provide some
physical context for when each category should be used. We then run a series of
N-body simulations, that include radiation forces acting on small grains, with
varying initial conditions across the three categories. We test the influence
of the initial parent body belt width, eccentricity, and alignment with the
planet on the resulting debris disc structure and compare the final peak
emission location, disc width and offset of synthetic disc images produced with
a radiative transfer code. We also track the evolution of the forced
eccentricity of the dust grains induced by the planet, as well as resonance
dust trapping. We find that an initially broad parent body belt always results
in a broader debris disc than an initially narrow parent body belt. While
simulations with a parent body belt with low initial eccentricity (e ~ 0) and
high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we
find that purely secular forced initial conditions, where the initial disc
eccentricity is set to the forced value and the disc is aligned with the
planet, always result in a narrower disc. We conclude that broad debris discs
can be modelled by using either a dynamically cold or dynamically warm parent
belt, while in contrast eccentric narrow debris rings are reproduced using a
secularly forced parent body belt.
