Background Exotic non-spherical nuclear pasta shapes are expected in nuclear matter at just below saturation density because of competition between short range nuclear attraction and long range Coulomb repulsion .

Purpose We explore the impact of nuclear pasta on nucleosynthesis , during neutron star mergers , as cold dense nuclear matter is ejected and decompressed .

Methods We perform classical molecular dynamics simulations with 51 200 and 409 600 nucleons , that are run on GPUs .
We expand our simulation region to decompress systems from an initial density of 0.080 \mathrm { fm } ^ { -3 } down to 0.00125 \mathrm { fm } ^ { -3 } .
We study proton fractions of Y _ { P } = 0.05 , 0.10 , 0.20 , 0.30 , and 0.40 at T = 0.5 , 0.75 , and 1.0 MeV .
We calculate the composition of the resulting systems using a cluster algorithm .

Results We find final compositions that are in good agreement with nuclear statistical equilibrium models for temperatures of 0.75 and 1 \mathrm { MeV } .
However , for proton fractions greater than Y _ { P } = 0.2 at a temperature of T = 0.5 \mathrm { MeV } , the MD simulations produce non-equilibrium results with large rod-like nuclei .

Conclusions Our MD model is valid at higher densities than simple nuclear statistical equilibrium models and may help determine the initial temperatures and proton fractions of matter ejected in mergers .