Starting from ϕ n , n = 1, and solving iteratively Eq. D1a for every element H α kl Ω β kl -H β kl Ω α kl (from k = 2, l = 1 and ascending) until deducing the expression of the coefficients C 1 (j), then using the same approach for n > 1, we obtain a formula that can be generalized, hence an expression for any coefficient