The write process was modelled as the sequential, cumulative addition of several PSF arrays, one for each laser pulse, with a translation of the array between pulses as required to model the beam scanning process. Proximity effects between light spots were allowed for by introducing a diffusion step (convolution by a 3D Gaussian function) between each laser pulse. Several diffusion processes are possible, notably molecular diffusion such as radical or inhibitor diffusion (but heat energy brought by the laser and exothermic chemical interactions could also be involved). Our digital modelling of this diffusion is simplistic and purely phenomenological, making no a priori assumptions about the underlying physico-chemical mechanisms: we simply assume a diffusion process takes place, and calculations show that the characteristic lifetime of the diffusing species are compatible with values reported for carbon centred radical species. Polymerization was modelled by thresholding the cumulated light energy dose during the process, applying non-linear functions as required to represent multi-photon processes. A sampling grid of 200 nm was chosen as a compromise between maintaining manageable computing loads and modelling the PSF functions with sufficient fidelity. Supplementary details regarding mathematical simulation and parameters are featured as SI.