There are two significant changes in the Grimme D3 scheme. The C 6ii coefficients are now geometry dependent: for each element, the value of C 6ii considers the coordination number. Second, there is the inclusion of an 8th order dispersion term. Generally speaking, the Grimme-D3 method is more accurate than Grimme-D2. As stated above, the reason we include Grimme-D2 in our analysis is because Quantum ESPRESSO