Interstellar dust grains [1] comprise only 1% of the mass in the molecular clouds of galaxies and yet catalyze the formation of many gas phase molecules, in particular H2 [2], which allows for the cooling and collapse of these clouds and the formation of stars and planets. High-energy radiation and particles from hot stars, supernovae, or active black holes can alter the physical properties of dust grains and thereby affect their role in these processes. There is no experimental study on grain-grain collisions, for grain smaller than tens of microns, except for clusters with less than 100 atoms. Studies at the mm/cm scale can be roughly understood by continuum models, but these models might break down at the nanometer scale. There are many atomistic molecular dynamics (MD) simulations on the destruction of 3D droplets due to large temperature input [3], 2D solids [4, 5], or collision of disks [6], but there are very few simulations on grain-grain collisions, never going beyond tens of atoms [7, 8]. Here we demonstrate how MD simulations of grain-grain collisions for grain with more than 100 atoms can be used to understand what happens for nanometer-sized grains, colliding at relatively low velocities
