  Mountains on rapidly rotating neutron stars efficiently radiate gravitational
waves. The maximum possible size of these mountains depends on the breaking
strain of neutron star crust. With multi-million ion molecular dynamics
simulations of Coulomb solids representing the crust, we show that the breaking
strain of pure single crystals is very large and that impurities, defects, and
grain boundaries only modestly reduce the breaking strain to around 0.1. Due to
the collective behavior of the ions during failure found in our simulations,
the neutron star crust is likely very strong and can support mountains large
enough so that their gravitational wave radiation could limit the spin periods
of some stars and might be detectable in large scale interferometers.
Furthermore, our microscopic modeling of neutron star crust material can help
analyze mechanisms relevant in magnetar giant and micro flares.
