2) The error with masstranport.jpg appeared because the iterative solution of the computation diverged. Unfortunately,
stability of the VR-NE computation is very sensitive to the mesh in the gas blocks in which the mass transport problem
is solved. In particular, one should mention the following:

2a) Only matched mesh on the internal interfaces of the gas domain is supported. If we run the computation starting from
your file "AXITRON_ini.vrp", the computation is stopped with the message
"Error: Mismatched grid on boundary "Boundary40" detected:
12 faces in block "Block6" and 8 faces in block "Block7"
Internal interfaces of the mass transport domain should have matched grids."

In "AXITRON_ini.vrp", flag "Automatic Mesh Generation" is checked. This option allows fast and easy generation of
reasonably fine triangular grid without manual specification of number of grid points along each boundary, but it is
important that it generates the grid independently in all blocks. As a result, it always generates mismatched grids. In
complex reactor geometries where the mass transport domain consists of several gas blocks, the interfaces between these
blocks must have matched grid, so the "Automatic Mesh Generation" option should not be used. The grid in gas blocks
should always be assigned by manual fragmentation of each boundary.
If mismatched grid is found on some of the internal boundaries of the gas domain, the computations stops with an error
message.

2b) Stability of the computation convergence is sensitive the grid structure. In particular, stability of the
computation that uses a rectangular grid is considerably higher than that using triangular grid. So it is strongly
recommended to split the gas domain into gas blocks that can be meshed by rectangular, or at least nearly-rectangular,
slightly skewed quadrilateral cells. In the example computation of Aixtron reactor, rectangular grid is used in nearly
all gas blocks.

2c) In Settings->Output Variables dialog window, the user can activate output of the residuals of all variables. This
option can be used if the computation diverges. The user can identify the zones where the grid should be improved by
checking the reactor zones where highest residuals are calculated.

2d) Usually, refinement of the grid, i.e. specification of smaller grid cells, raises the computation accuracy. However,
sometimes assigning too small cells may lead to the divergence of the computation that converges successfully on a grid
with larger cells. So, if the cell size is considerably changed, modification of the Relaxation and Inertial Factor
parameters may be required to reach the convergence.

2e) The grid in the examples supplied with VR-Nitride Edition has been optimized to obtain stable computation
convergence. It can be used as an example by the users when grid in other reactors is generated.

3) Computation convergence also depends on the initial distribution and selection of the carrier species. In your
example, gas material "Mixture_AlGaN_Mixture" contained N2 with mass fraction of 1, whereas H2, NH3 and TMGa were
supplied at the inlet. The values specified in the Gas material mixture are used as the initial gas mixture composition
at the first iteration. If the computation converges successfully, the final results do not depend on the initial gas
mixture composition. However, the initial gas mixture may affect the convergence rate and even lead to divergence. It is
recommended to set value of 1 to the mass fraction of the actual carrier gas (in your example, this is H2), or to
distribute the species fractions proportionally to the total flow rates supplied at the inlets.