I am trying to use the DFT software such as Quantum espresso or VASP to study the grain boundary effect on the thermal and electrical transport properties of alloy. However, I am not sure what size of the system should be suitable to yield accurate result if I include the grain boundary. Is there anyone has similar experience on that? Thanks very much!
Dear Dr. Wagner:
I need the relaxation time Tau calculated from the ab-initio method. Then I will use the BoltzTrap to calculate the thermal and electrical conductivity. Thanks.
Best,
Jiaqi
It is clear that the system must be very large in order to reduce the size effects of the system periodicity. Your system is an alloy and you have to identify the most stable configuration for a supercell with the size of considered grains. Moreover, you have to take into account the possible segregation phenomena at the grain boundaries. You have to find the best compromise between the system size, calculation accuracy and the computing resources, which depends on the nature of the investigated material and the size and orientation of the two grains. Maybe, you can consider tight-binding methods or reacting empirical force fields, at least to find the proper structure of the grain boundary.
Ah, interesting -- you mean https://www.researchgate.net/publication/222835431, right? As far as I can see from this paper, this method works for a homogeneous material. Therefore I don't see (and I really mean it like that -- maybe I just overlook something) how you could include a grain boundary in such a calculation.
Therefore, some words about the physics: To describe the effect of a grain boundary on thermal transport I would look for the interaction of phonons with their "surroundings" (in a broad general sense). From refereeing their manuscripts I know such aspects are discussed, e.g., by Lindsay et al. (https://www.researchgate.net/publication/258015539) and Fugallo et al. (https://www.researchgate.net/publication/233815827). How would your intended study of grain boundary effects on the atomic level compare with the atomic level effects treated in these papers: Which effects would have to be treated on equal footing, which could be handled differently (e.g. non-atomically on a mesoscopic or macroscopic scale)?
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