# Calculation of Thermal Accommodation Coefficient

Dear all,

I try to calculate thermal accommodation coefficient (TAC) in a better way.

Now, I can calculate it from the dump file using my own matlab code, but it takes a lot of time (reading dump file via matlab code) since my dump file size is about 1-2 GB (including the coordinate and KE of each atom).

I think we could write a short script using “if” statement in input file to dump KE of specific atom passing a certain coordinate, let’s if z coordinate of atom 1 > 10, we can dump KE of atom 1 to the file.

Can you provide an example code (or some idea) how to start?

Thanks, Gisuk.

The dump modify command has a thresh option which

can choose a subset of atoms to dump based on a per-atom

critierion. The KE of the atom could be that critrerion

if you use compute ke/atom as the thresh param.

Steve

I looked up the definition of TAC, and it seems to be a somewhat murky concept, but it seems to be related to the average energy transferred by hot gas particles to a cold solid surface during collisions. If you ignore the potential energy of particles, then it is sufficient to track the kinetic energy of gas particles. The simplest thing to do is to dump ke/atom for all atoms at time intervals tau that is shorter than the mean free path time of the particles. There are some basic dump filter tricks to making this more efficient:

1. Do not dump non-gas particles
2. Only dump gas particles in a layer near the surface, which excludes particles that have not recently collided with the wall or will not soon collide with the wall.
3. To implement the if statement idea, you can use dump_modify with a region and a threshold on velocity direction

dump_modify reflected region reflectedlayer thresh vz > 0.0

dump_modify incident region incidentlayer thresh vz < 0.0

Aidan