4.4. Boundary Conditions - Particle Solver

Within the parameter file it is possible to define different particle boundary conditions. The number of boundaries is defined by

Part-nBounds = 2
Part-Boundary1-SourceName   = BC_OPEN
Part-Boundary1-Condition    = open
Part-Boundary2-SourceName   = BC_WALL
Part-Boundary2-Condition    = reflective

The Part-Boundary1-SourceName= corresponds to the name given during the preprocessing step with HOPR. The available conditions (Part-Boundary1-Condition=) are described in the table below.

Condition	Description
`open`	Every particle crossing the boundary will be deleted
`symmetric`	A perfect specular reflection, without sampling of particle impacts
`reflective`	Definition of different surface models: Section Reflective Wall, Section Surface Chemistry, Section Catalytic Surfaces
`rot_periodic`	Definition of rotational periodicity: Section Rotational Periodicity
`rot_periodic_inter_plane`	Extension of rotational periodicity, allowing non-conformal interfaces and varying periodicity

4.4.1. Reflective Wall

A reflective boundary can be defined with

Part-Boundary2-SourceName   = BC_WALL
Part-Boundary2-Condition    = reflective

A perfect specular reflection is performed, if no other parameters are given. Gas-surface interactions can be modelled with the extended Maxwellian model [11], using accommodation coefficients of the form

\[\alpha = \frac{E_i-E_r}{E_i - E_w}\]

where \(i\), \(r\) and \(w\) denote the incident, reflected and wall energy, respectively. The coefficient MomentumACC is utilized to decide whether a diffuse (MomentumACC \(>R\)) or specular reflection (MomentumACC \(<R\)) occurs upon particle impact, where \(R=[0,1)\) is a random number. Separate accommodation coefficients can be defined for the translation (TransACC), rotational (RotACC), vibrational (VibACC) and electronic energy (ElecACC) accommodation at a constant wall temperature [K].

Part-Boundary2-MomentumACC  = 1.
Part-Boundary2-WallTemp     = 300.
Part-Boundary2-TransACC     = 1.
Part-Boundary2-VibACC       = 1.
Part-Boundary2-RotACC       = 1.
Part-Boundary2-ElecACC      = 1.

An additional option Part-Boundary2-SurfaceModel is available, that is used for heterogeneous reactions (reactions that have reactants in two or more phases) or secondary electron emission models. These models are described in detail in Section Surface Chemistry.

4.4.1.1. Wall movement (Linear & rotational)

Additionally, a linear wall velocity [m/s] can be given

Part-Boundary2-WallVelo = (/0,0,100/)

In the case of rotating walls the -RotVelo flag, a rotation frequency [Hz], and the rotation axis (x=1, y=2, z=3) must be set. Note that the definition of the rotational direction is defined by the sign of the frequency using the right-hand rule.

Part-Boundary2-RotVelo = T
Part-Boundary2-RotFreq = 100
Part-Boundary2-RotAxis = 3

The wall velocity will then be superimposed onto the particle velocity.

4.4.1.2. Linear temperature gradient

A linear temperature gradient across a boundary can be defined by supplying a second wall temperature and the start and end vector as well as an optional direction to which the gradient shall be limited (default: 0, x = 1, y = 2, z = 3)

Part-Boundary2-WallTemp2      = 500.
Part-Boundary2-TempGradStart  = (/0.,0.,0./)
Part-Boundary2-TempGradEnd    = (/1.,0.,1./)
Part-Boundary2-TempGradDir    = 0

In the default case of the TempGradDir = 0, the temperature will be interpolated between the start and end vector, where the start vector corresponds to the first wall temperature WallTemp, and the end vector to the second wall temperature WallTemp2. Position values (which are projected onto the temperature gradient vector) beyond the gradient vector utilize the first (Start) and second temperature (End) as the constant wall temperature, respectively. In the special case of TempGradDir = 1/2/3, the temperature gradient will only be applied along the chosen the direction. As oppposed to the default case, the positions of the surfaces are not projected onto the gradient vector before checking wether they are inside the box spanned by TempGradStart and TempGradEnd. The applied surface temperature is output in the DSMCSurfState as Wall_Temperature for verification.

4.4.1.3. Radiative equilibrium

Another option is to adapt the wall temperature based on the heat flux assuming that the wall is in radiative equilibrium. The temperature is then calculated from

\[ q_w = \varepsilon \sigma T_w^4,\]

where \(\varepsilon\) is the radiative emissivity of the wall (default = 1) and \(\sigma = \pu{5.67E-8 Wm^{-2}K^{-4}}\) is the Stefan-Boltzmann constant. The adaptive boundary is enabled by

Part-AdaptWallTemp = T
Part-Boundary1-UseAdaptedWallTemp = T
Part-Boundary1-RadiativeEmissivity = 0.8

If provided, the wall temperature will be adapted during the next output of macroscopic variables, where the heat flux calculated during the preceding sampling period is utilized to determine the side-local temperature. The temperature is included in the State file and thus available during a restart of the simulation. The surface output (in DSMCSurfState) will additionally include the temperature distribution in the Wall_Temperature variable (see Section Particle Flow and Surface Sampling). To continue the simulation without further adapting the temperature, the first flag has to be disabled (Part-AdaptWallTemp = F). It should be noted that the the adaptation should be performed multiple times to achieve a converged temperature distribution.

4.4.2. Rotational Periodicity

The rotational periodic boundary condition can be used in order to reduce the computational effort in case of an existing rotational periodicity. In contrast to symmetric boundary conditions, a macroscopic flow velocity in azimuthal direction can be simulated (e.g. circular flow around a rotating cylinder). Exactly two corresponding boundaries must be defined by setting rot_periodic as the BC condition and the rotating angle for each BC. Multiple pairs of boundary conditions with different angles can be defined.

Part-Boundary1-SourceName       = BC_Rot_Peri_plus
Part-Boundary1-Condition        = rot_periodic
Part-Boundary1-RotPeriodicAngle = 90.

Part-Boundary2-SourceName       = BC_Rot_Peri_minus
Part-Boundary2-Condition        = rot_periodic
Part-Boundary2-RotPeriodicAngle = -90.

CAUTION! The correct sign for the rotating angle must be determined. The position of particles that cross one rotational periodic boundary is tranformed according to this angle, which is defined by the right-hand rule and the rotation axis:

Part-RotPeriodicAxi = 1    ! (x = 1, y = 2, z = 3)

The usage of rotational periodic boundary conditions is limited to cases, where the rotational periodic axis is one of the three Cartesian coordinate axis (x, y, z) with its origin at (0, 0, 0).

4.4.2.1. Intermediate Plane Definition

If several segments with different rotation angles are defined, exactly two corresponding BCs must be defined for each segment. Since the plane between these segments with different rotational symmetry angles represents a non-conforming connection, additional two BCs must be defined as rot_periodic_inter_plane at this intermediate plane. Both BCs must refer to each other in the definition in order to ensure the connection.

Part-Boundary40-SourceName       = BC_INT_R1_BOT
Part-Boundary40-Condition        = rot_periodic_inter_plane
Part-Boundary40-AssociatedPlane  = 41

Part-Boundary41-SourceName       = BC_INT_S1_TOP
Part-Boundary41-Condition        = rot_periodic_inter_plane
Part-Boundary41-AssociatedPlane  = 40

Note that using the intermediate plane definition with two corresponding BCs allows the user to mesh the segments independently, creating a non-conforming interface at the intermediate plane. However, use of these non-conformal grids is so far only possible in standalone DSMC simulations.

4.4.3. Porous Wall / Pump

The porous boundary condition uses a removal probability to determine whether a particle is deleted or reflected at the boundary. The main application of the implemented condition is to model a pump, according to [12]. It is defined by giving the number of porous boundaries and the respective boundary number (BC=2 corresponds to the BC_WALL boundary defined in the previous section) on which the porous condition is.

Surf-nPorousBC=1
Surf-PorousBC1-BC=2
Surf-PorousBC1-Type=pump
Surf-PorousBC1-Pressure=5.
Surf-PorousBC1-PumpingSpeed=2e-9
Surf-PorousBC1-DeltaPumpingSpeed-Kp=0.1
Surf-PorousBC1-DeltaPumpingSpeed-Ki=0.0

Currently, two porous BC types are available, pump and sensor. For the former, the removal probability is determined through the given pressure [Pa] at the boundary. A pumping speed can be given as a first guess, however, the pumping speed \(S\) [\(m^3/s\)] will be adapted if the proportional factor (\(K_{\mathrm{p}}\), DeltaPumpingSpeed-Kp) is greater than zero

\[ S^{n+1}(t) = S^{n}(t) + K_{\mathrm{p}} \Delta p(t) + K_{\mathrm{i}} \int_0^t \Delta p(t') dt',\]

where \(\Delta p\) is the pressure difference between the given pressure and the actual pressure at the pump. An integral factor (\(K_{\mathrm{i}}\), DeltaPumpingSpeed-Ki) can be utilized to mimic a PI controller. The proportional and integral factors are relative to the given pressure. However, the integral factor has not yet been thoroughly tested. The removal probability \(\alpha\) is then calculated by

\[\alpha = \frac{S n \Delta t}{N_{\mathrm{pump}} w} \]

where \(n\) is the sampled, cell-local number density and \(N_{\mathrm{pump}}\) is the total number of impinged particle at the pump during the previous time step. \(\Delta t\) is the time step and \(w\) the weighting factor. The pumping speed \(S\) is only adapted if the resulting removal probability \(\alpha\) is between zero and unity. The removal probability is not species-specific.

To reduce the influence of statistical fluctuations, the relevant macroscopic values (pressure difference \(\Delta p\) and number density \(n\)) can be sampled for \(N\) iterations by defining (for all porous boundaries)

AdaptiveBC-SamplingIteration=10

A porous region on the specified boundary can be defined. At the moment, only the circular option is implemented. The origin of the circle/ring on the surface and the radius have to be given. In the case of a ring, a maximal and minimal radius is required (-rmax and -rmin, respectively), whereas for a circle only the input of maximal radius is sufficient.

Surf-PorousBC1-Region=circular
Surf-PorousBC1-normalDir=1
Surf-PorousBC1-origin=(/5e-6,5e-6/)
Surf-PorousBC1-rmax=2.5e-6

The absolute coordinates are defined as follows for the respective normal direction.

Normal Direction	Coordinates
x (=1)	(y,z)
y (=2)	(z,x)
z (=3)	(x,y)

Using the regions, multiple pumps can be defined on a single boundary. Additionally, the BC can be used as a sensor by defining the respective type:

Surf-PorousBC1-BC=3
Surf-PorousBC1-Type=sensor

Together with a region definition, a pump as well as a sensor can be defined on a single and/or multiple boundaries, allowing e.g. to determine the pressure difference between the pump and a remote area of interest.

4.4.4. Surface Chemistry

Modelling of reactive surfaces is enabled by setting Part-BoundaryX-Condition=reflective and an appropriate particle boundary surface model Part-BoundaryX-SurfaceModel:

Part-Boundary1-SurfaceModel = 0

The available conditions (Part-BoundaryX-SurfaceModel=) are described in the table below, ranging from simple empirical models and secondary electron/ion emission to finite-rate catalysis modelling including a surface treatment.

Model	Description
0 (default)	Standard extended Maxwellian scattering
1	Empirical modelling of sticking coefficient/probability
2	Fixed probability surface chemistry
5	Secondary electron emission as given by Ref. [13].
7	Secondary electron emission due to ion impact (SEE-I with \(Ar^{+}\) on different metals) as used in Ref. [14] and given by Ref. [15] with a default yield of 13 %.
8	Secondary electron emission due to ion impact (SEE-E with \(e^{-}\) on dielectric surfaces) as used in Ref. [16] and given by Ref. [17].
9	Secondary electron emission due to ion impact (SEE-I with \(Ar^{+}\)) with a constant yield of 1 %. Emitted electrons have an energy of 6.8 eV upon emission.
10	Secondary electron emission due to ion impact (SEE-I with \(Ar^{+}\) on copper) as used in Ref. [18] originating from [19]
11	Secondary electron emission due to electron impact (SEE-E with \(e^{-}\) on quartz (SiO\(_{2}\))) as described in Ref. [20] originating from [21]
20	Finite-rate catalysis model, Section Catalytic Surfaces

For surface sampling output, where the surface is split into, e.g., \(3\times3\) sub-surfaces, the following parameters mus be set

BezierSampleN                 = 3
DSMC-nSurfSample              = 3
Part-WriteMacroSurfaceValues  = T
Particles-DSMC-CalcSurfaceVal = T
Part-IterationForMacroVal     = 200

where BezierSampleN=DSMC-nSurfSample. In this example, sampling is performed over and every 200 iterations.

4.4.4.1. Empirical model for a sticking coefficient

To model the sticking of gas particles on cold surfaces, an empirical model is available, which is based on experimental measurements. The sticking coefficient is modelled through the product of a non-bounce probability \(B(\alpha)\) and a condensation probability \(C(\alpha,T)\)

\[ p_s (\alpha,T) = B(\alpha) C(\alpha,T) \]

The non-bounce probability introduces a linear dependency on the impact angle \(\alpha\)

\[\begin{split} B(\alpha) = \begin{cases} 1 , & |\alpha| < \alpha_{\mathrm{B}} \\ \dfrac{90^{\circ}-|\alpha|}{90^{\circ}-|\alpha_{\mathrm{B}}|} , & \alpha_{\mathrm{B}} \leq |\alpha| \leq 90^{\circ} \\ \end{cases} \end{split}\]

\(\alpha_{\mathrm{B}}\) is a model-dependent cut-off angle. The condensation probability introduces a linear dependency on the surface temperature \(T\)

\[\begin{split} C(\alpha, T) = \begin{cases} 1 , & T < T_1 \\ \dfrac{T_2(\alpha)-T}{T_2(\alpha)-T_1(\alpha)} , & T_1 \leq T \leq T_2 \\ 0 , & T > T_2 \\ \end{cases} \end{split}\]

The temperature limits \(T_1\) and \(T_2\) are model parameters and can be given for different impact angle ranges defined by the maximum impact angle \(\alpha_{\mathrm{max}}\). These model parameters are read-in through the species database and have to be provided in the /Surface-Chemistry/StickingCoefficient dataset in the following format (example values):

\(\alpha_{\mathrm{max}}\) [deg]	\(\alpha_{\mathrm{B}}\) [deg]	\(T_1\) [K]	\(T_2\) [K]
45	80	50	100
90	70	20	50

In this example, within impact angles of \(0°\leq\alpha\leq45°\), the model parameters of the first row will be used and for \(45°<\alpha\leq90°\) the second row. The number of rows is not limited. The species database is read-in by

Particles-Species-Database = SpeciesDatabase.h5

As additional output, the cell-local sticking coefficient will be added to the sampled surface output. A particle sticking to the surface will be deleted and its energy added to the heat flux sampling. This model can be combined with the linear temperature gradient and radiative equilibrium modelling as described in Section Reflective Wall.

4.4.4.2. Fixed probability surface chemistry

This simple fixed-probability surface chemistry model allows the user to define arbitrary surface reactions, by defining the impacting species, the products and a fixed event probability. The reaction is then assigned to the boundaries by specifying their number and index as defined previously.

Surface-Reaction1-Type               = P
Surface-Reaction1-Reactants          = (/1,0/)
Surface-Reaction1-Products           = (/2,1,0/)
Surface-Reaction1-EventProbability   = 0.25
Surface-Reaction1-NumOfBoundaries    = 2
Surface-Reaction1-Boundaries         = (/1,3/)

Optionally, a reaction-specific accommodation coefficient for the products can be defined, otherwise the surface-specific accommodation will be utilized for the product species:

Surface-Reaction1-ProductAccommodation = 0.

In the case that the defined event does not occur, a regular interaction using the surface-specific accommodation coefficients is performed. Examples are provided as part of the regression tests: regressioncheck/NIG_DSMC/SURF_PROB_DifferentProbs and regressioncheck/NIG_DSMC/SURF_PROB_MultiReac.

4.4.4.3. Secondary Electron Emission (SEE)

Different models are implemented for secondary electron emission that are based on either electron or ion bombardment, depending on the surface material. All models require the specification of the electron species that is emitted from the surface via

Part-SpeciesA-PartBoundB-ResultSpec = C

where electrons of species C are emitted from boundary B on the impact of species A.

4.4.4.3.1. Model 5

The model by Levko [13] can be applied for copper electrodes for electron and ion bombardment and is activated via Part-BoundaryX-SurfaceModel=5. For ions, a fixed emission yield of 0.02 is used and for electrons an energy-dependent function is employed.

4.4.4.3.2. Model 7

The model by Depla [15] can be used for various metal surfaces and features a default emission yield of 13 % and is activated via Part-BoundaryX-SurfaceModel=7 and is intended for the impact of \(Ar^{+}\) ions. For more details, see the original publication.

The emission yield and energy can be varied for this model by setting

SurfModEmissionYield  = 1.45 ! ratio of emitted electron flux vs. impacting ion flux [-]
SurfModEmissionEnergy = 6.8  ! [eV]

respectively. The emission yield represents the ratio of emitted electrons vs. impacting ions and the emission energy is given in electronvolts. If the energy is not set, the emitted electron will have the same velocity as the impacting ion.

Additionally, a uniform energy distribution function for the emitted electrons can be set via

SurfModEnergyDistribution = uniform-energy

which will scale the energy of the emitted electron to fit a uniform distribution function.

4.4.4.3.3. Model 8

The model by Morozov [17] can be applied for dielectric surfaces and is activated via Part-BoundaryX-SurfaceModel=8 and has an additional parameter for setting the reference electron temperature (see model for details) via Part-SurfaceModel-SEE-Te, which takes the electron temperature in Kelvin as input (default is 50 eV, which corresponds to 11604 K). The emission yield is determined from an energy-dependent function. The model can be switched to an automatic determination of the bulk electron temperature via

Part-SurfaceModel-SEE-Te-automatic = T ! Activate automatic bulk temperature calculation
Part-SurfaceModel-SEE-Te-Spec      = 2 ! Species ID used for automatic temperature calculation (must correspond to electrons)

where the species ID must be supplied, which corresponds to the electron species for which, during Part-AnalyzeStep, the global translational temperature is determined and subsequently used to adjust the energy dependence of the SEE model. The global (bulk) electron temperature is written to PartAnalyze.csv as XXX-BulkElectronTemp-[K].

4.4.4.3.4. Model 10

An energy-dependent model of secondary electron emission due to \(Ar^{+}\) ion impact on a copper cathode as used in Ref. [18] originating from [19] is activated via Part-BoundaryX-SurfaceModel=10. For more details, see the original publications.

4.4.4.3.5. Model 11

An energy-dependent model (linear and power fit of measured SEE yields) of secondary electron emission due to \(e^{-}\) impact on a quartz (SiO\(_{2}\)) surface as described in Ref. [20] originating from [21] is activated via Part-BoundaryX-SurfaceModel=11. For more details, see the original publications.

4.4.5. Catalytic Surfaces

Catalytic reactions can be modeled in PICLas using a finite-rate reaction model with an implicit treatment of the reactive surface. For a better resolution of the parameters, the catalytic boundaries are discretized into a certain number of subsides. A definition of the boundary temperature in the parameter input file is required in all cases. Different types of surfaces can be defined by the lattice constant of the unit cell Part-BoundaryX-LatticeVec and the number of particles in the unit cell Part-BoundaryX-NbrOfMol-UnitCell. These parameters are used in the calculation of the number of active sites.

By default, the simulation is started with a clean surface, but an initial species-specific coverage can be specified by Part-BoundaryX-SpeciesX-Coverage, which represents the relative number of active sites that are occupied by adsorbate particles. Maximum values for the coverage values can be specified by:

Part-Boundary1-Species1-MaxCoverage
Part-Boundary1-MaxTotalCoverage

Multi-layer adsorption is enabled by a maximal total coverage greater than 1.

The reaction paths are defined in the input parameter file. First, the number of gas-surface reactions to be read in must be defined:

Surface-NumOfReactions = 2

A catalytic reaction and the boundary on which it takes place is then defined by

Surface-Reaction1-SurfName           = Adsorption
Surface-Reaction1-Type               = A
Surface-Reaction1-Reactants          = (/1,0/)
Surface-Reaction1-Products           = (/2,1,0/)
Surface-Reaction1-NumOfBoundaries    = 2
Surface-Reaction1-Boundaries         = (/1,3/)

All reactants and products are defined by their respective species index. In the case of multiple reacting, the order does not influence the input. The following options are available for the catalytic reaction type:

Model	Description
A	Adsorption: Kisliuk or Langmuir model
D	Desorption: Polanyi-Wigner model
ER	Eley-Rideal reaction: Arrhenius based chemistry
LH	Langmuir-Hinshelwood reaction: Arrhenius based chemistry
LHD	Langmuir-Hisnhelwood reaction with instantaneous desorption

For the treatment of multiple reaction paths of the same species, a possible bias in the reaction rate is avoided by a randomized treatment. Bulk species can participate in the reaction. In this case, the bulk species is defined by Surface-Species and the corresponding species index. All reaction types allow for the definition of a reaction enthalpy. In addition, this value can be linearly increased (negative factor) or decreased (positive factor) by a scaling factor for the heat of reaction. Both values are given in [K].

Surface-Reaction1-ReactHeat      = 17101.4
Surface-Reaction1-HeatScaling    = 1202.9

Depending on the reaction type, different additional parameters have to be defined. More details on the specific cases are given in the following subsections. An example input file for CO and O2 on a palladium surface can be found in the regression tests regressioncheck/WEK_DSMC/ChannelFlow_SurfChem_AdsorpDesorp_CO_O2.

4.4.5.1. Adsorption

For the modelling of the adsorption of a gas particle on the surface, two models are available: the simple Langmuir model, with a linear dependence of the adsorption probability on the surface coverage, and the precursor-based Kisliuk model:

\[ S = S_0 (1 + K (1/\theta^{\alpha} - 1))^{-1}\]

Here, \(S_0\) is the binding coefficient for a clean surface, \(\alpha\) is the dissociation constant (2 for dissociative adsorption) and \(K\) is the equilibrium constant between adsorption and desorption from the precursor state. For \(K = 1\), the model simplifies to the Langmuir case. The parameters can be defined in PICLas as follows:

Surface-Reaction1-StickingCoefficient  = 0.2
Surface-Reaction1-DissOrder            = 1
Surface-Reaction1-EqConstant           = 0.6

A special case of adsorption is the dissociative adsorption (Surface-ReactionX-DissociativeAdsorption = true), where only half of the molecule binds to the surface, while the other half remains in the gas phase. The adsorbate half Surface-ReactionX-AdsorptionProduct and the gas phase product Surface-ReactionX-GasPhaseProduct are specified by their respective species indices. The adsorption probability is calculated analogously to the general case.

Lateral interactions between multiple adsorbate species, which can disfavor further adsorption can be taken into account by the command Surface-ReactionX-Inhibition and the species index of the inhibiting species.

4.4.5.2. Desorption

The desorption of an adsorbate particle into the gas phase is modelled by the Polanyi-Wigner equation.

\[k(T) = A T^b \theta^{\alpha}_{A} e^{-E_\mathrm{a}/T}\]

where \(A\) is the prefactor ([1/s, m\(^2\)/s] depending on the dissociation constant), \(\alpha\) the dissociation constant and \(E_\mathrm{a}\) the activation energy [K]. These parameters can be defined in PICLas as follows:

Surface-ReactionX-Prefactor
Surface-ReactionX-Energy

4.4.5.3. Catalytic Reaction

The Eley-Rideal and the Langmuir-Hinshelwood reaction use Arrhenius-type reaction rates along with the coverage of all surface-bound reactants \(\theta_{AB}\), to reproduce of the catalytic reaction.

\[k(T) = A T^b \theta_{AB} e^{-E_\mathrm{a}/T}\]

The Arrhenius prefactor ([m\(^3\)/s] for the Eley-Rideal reaction and [m\(^2\)/s] for the Langmuir-Hinshelwood case) and the activation energy are read in analogously to the desorption case. For the reactions, an energy accommodation coefficient Surface-ReactionX-EnergyAccommodation with values between 0 and 1 can be specified, which defines the amount of the reaction energy that is transferred to the surface.

In the general Langmuir-Hinshelwood case with the reaction type LH, the product species stays adsorbed on the surface, until a desorption takes place in a later step. For reactions in combination with very high desorption rates, the reaction type LHD is more fitting. The product species are inserted directly into the gas phase without an intermediate desorption step.

Example inputs for both catalytic reactions can be found in the regression tests: regressioncheck/NIG_Reservoir/CAT_RATES_ER and regressioncheck/NIG_Reservoir/CAT_RATES_LH.

4.4.5.4. Diffusion

With Surface-Diffusion = true an instantaneous diffusion over all catalytic boundaries is enabled. This is equivalent to an averaging of the coverage values for all surface subsides.

4.4.5.5. Parameter Read-In from the Species Database

All information about a catalytic reaction can be retrieved from the species database. Here the catalytic reaction parameters are stored in containers and accessed via the reaction name, e.g. Adsorption_CO_Pt.

4.4.6. Deposition of Charges on Dielectric Surfaces

Charged particles can be absorbed (or reflected and leave their charge behind) at dielectric surfaces when using the deposition method cell_volweight_mean. The boundary can be used by specifying

```
Part-Boundary1-Condition         = reflective
Part-Boundary1-Dielectric        = T
Part-Boundary1-NbrOfSpeciesSwaps = 3
Part-Boundary1-SpeciesSwaps1     = (/1,0/) ! e-
Part-Boundary1-SpeciesSwaps2     = (/2,2/) ! Ar
Part-Boundary1-SpeciesSwaps3     = (/3,2/) ! Ar+
```

which sets the boundary dielectric and the given species swap parameters effectively remove electrons (\(e^{-}\)) on impact, reflect \(Ar\) atoms and neutralize \(Ar^{+}\) ions by swapping these to \(Ar\) atoms. Note that currently only singly charged particles can be handled this way. When multiple charged particles would be swapped, their complete charge mus be deposited at the moment.

The boundary must also be specified as an inner boundary via

BoundaryName                     = BC_INNER
BoundaryType                     = (/100,0/)

or directly in the hopr.ini file that is used for creating the mesh.