Shiva: the dust destruction model
  We present a numerical tool Shiva designed to simulate the dust destruction
in warm neutral, warm ionized, and hot ionized media under the influence of
photo-processing, sputtering, and shattering. The tool is designed primarily to
study the evolution of hydrogenated amorphous carbons (HACs), but options to
simulate polycyclic aromatic hydrocarbons (PAHs), silicate and graphite grains
are also implemented. HAC grain photo-processing includes both dehydrogenation
and carbon atom loss. Dehydrogenation leads to material transformation from
aliphatic to aromatic structure. Simultaneously, some other physical properties
(band gap energy, optical properties, etc.) of the material change as well. The
Shiva tool allows calculating the time-dependent evolution of the dust size
distribution depending on hydrogen, helium, and carbon number densities and
ionization state, gas temperature, radiation flux, relative gas-dust and
grain-grain velocities. For HAC grains the evolution of band gap energy
distribution is also computed. We describe a dust evolution model, on which the
tool relies, and present evolutionary time-scales for dust grains of different
sizes depending on external conditions. This allows a user to estimate quickly
a lifetime of a specific dust grain under relevant conditions. As an example of
the tool usage, we demonstrate how grain properties and corresponding infrared
spectra evolve in photo-dissociation regions, H II regions, and supernova
remnant shocks.
