  Charged particles are constantly accelerated to non-thermal energies by the
reconnecting magnetic field in the solar atmosphere. Our understanding of the
interactions between the particles and their environment can benefit from
three-dimensional atmospheric simulations accounting for non-thermal particle
beams. In a previous publication, we presented the first results from such a
simulation. However, the original treatment of beam propagation ignores
potentially important phenomena. Here, we present a more general beam
propagation model incorporating magnetic gradient forces, the return current,
acceleration by the ambient electric field, and temperature-dependent collision
rates. Neglecting collisional velocity randomisation makes the model
sufficiently lightweight to simulate millions of beams. We investigate how each
new physical effect changes beam energy transport in a three-dimensional
atmosphere. We applied the method of characteristics to the steady-state
continuity equation for electron flux to derive ordinary differential equations
for the mean evolution of energy, pitch angle, and flux with distance. For each
beam, we solved these numerically for a range of initial energies to obtain the
evolving flux spectrum, from which we computed the energy deposited into the
ambient plasma. Magnetic gradient forces significantly influence the deposition
of beam energy. The strong magnetic field convergence leads to a small coronal
deposition peak followed by a heavy dip caused by the onset of magnetic
mirroring. Mirrored electrons carry away 5 to 10% of the injected beam energy
on average. The transition region peak produced by the remaining energetic
electrons occurs slightly deeper than in a uniform magnetic field. An initial
diverging magnetic field enhances the subsequent impact of mirroring. The other
new physical effects are less significant for the studied atmospheric
conditions.
