I am trying to model the Seebeck coefficient and the electrical conductivity and lattice thermal conductivity for a thermoelectric material from the BTE using the RTA. I have two questions. 1. I am going to calculate each band separately and add. The electrical conductivity per band can be added together to find the total conductivity. However, the I saw in one paper that the total Seebeck coefficient is weighted by the electrical conductivity weighted average of the of the Seebeck coefficient per unit band. Why is this? 2. I am working with a material that has many grain boundaries. After I calculate the bulk crystalline properties, is there any way that I can include the effect of the grain boundaries on the lattice thermal conductivity? I know the average grain size and I would like a way to model this.