field ionization of compound (such as SiO2)

[xh-ui]

Dear all,

I want to simulate the field ionization of SiO2. Is it OK just to set the atom fraction to be 1:2 ? Is the energy gap,or say the ionisation and binding energies of such kind of compound included in EPOCH physics_packages/TABLES directory？

@Status-Mirror Thank you!

[Status-Mirror]

Hi @xh-ui,

The EPOCH ionisation routines consider isolated atoms instead of molecules. To simulate field ionisation of SiO2, you should define separate Si and O species.

To show how this is done, I have modified the field ionisation demo in our documentation. If we assume SiO2 has a density of 2650 kg/m³, and an SiO2 molecule has a mass of 60u, then SiO2 has a number density of $2.7\times 10^{28} \text{ m}^{-3}$. For each molecule, there is 1 Si and 2 O, so the densities for these species are: $2.7\times 10^{28} \text{ m}^{-3}$ and $5.3\times 10^{28} \text{ m}^{-3}$ respectively.

A simple input deck would take the following form:

begin:control
  nx = 128
  npart = 20 * nx
  t_end = 42.4e-15
  x_min = 0
  x_max = 4.0e-6
  field_ionisation = T
end:control

begin:boundaries
  bc_x_min = simple_laser
  bc_x_max = open
end:boundaries

begin:laser
  boundary = x_min
  intensity = 3.0e15 * 1.0e4
  lambda = 800.0e-9
  t_profile = 1
  t_end = 10.7e-15
end:laser

begin:species
  name = Si
  charge = 0
  atomic_no = 14
  mass = 1836.2 * 28.0
  frac = 0.5
  rho = if ((x lt 3.30e-6) and (x gt 3.05e-6), 2.7e28, 0)
  ionise = T
  electron_species = Electron
end:species

begin:species
  name = O
  charge = 0
  atomic_no = 8
  mass = 1836.2 * 16.0
  frac = 0.5
  rho = if ((x lt 3.30e-6) and (x gt 3.05e-6), 5.3e28, 0)
  ionise = T
  electron_species = Electron
end:species

begin:species
  name = Electron
  frac = 0
  identify:electron
end:species

begin:output
  dt_snapshot = t_end/100
  number_density = always + species
end:output

Hope this helps, Stuart

[Hnair13]

Hello @Status-Mirror in this given input deck don't we have to specify the electron properties in another species block?

[Status-Mirror]

Hi @Hnair13,

We do specify the electron properties, here:

begin:species
  name = Electron
  frac = 0
  identify:electron
end:species

In the input deck I provide, we start with neutral non-ionised silicon and oxygen - there are no free electrons in the system we need to load. As the target is ionised, the ionisation routines will start to populate our empty Electron species with ejected macro-electrons.

Cheers, Stuart

[TomGoffrey]

Just to add, from a not particularly rigorous search, the disassociation energy of SiO2 is lower than the ionisation energies of their constituent parts (although possibly not dramatically so), so the approach @Status-Mirror suggests is reasonable.

[xh-ui]

Thank you for your answer. I think I have understanded it.