Thermal diffusion coefficient (thermal diffusivity) does has the same
dimensions as mass diffusion coefficient, but they are not the same thing.
For your bilayer material, mass diffusion coefficient should be zero
because it is a solid. If you got a nonzero value, then something is wrong.
You can post detailed results if you have further questions on this.
孙琳 <sunlin18@xxxxxxxxxx> 于 2020年7月5日周日 12:39写道：
Recently, I've done some EMD simulations for twisted bilayer graphene
(tBLG) with GPUMD-2.4-correction. When calculating the PDOS with velocity
autocorrelation function VAC, I learned that the diffusion constant could
also be induced by the integral of the running VAC.
I have just learned MD for two months, so I'm not very clear with the
physical meaning of the diffusion constant. Is this diffusion constant
identical to the thermal diffusion coefficient? Intuitively, the calculated
diffusion constant is related to the atom's motion rather than phonon's
motion. However, not only the unit but also the value of the calculated
diffusion constant is almost the same as those of tBLG's thermal diffusion
coefficient. Thus, can I regard the calculated diffusion constant as the
thermal diffusion coefficient?
Thank you very much, and I'm looking forward for your kindly response.