Hi all, I have a few questions about calculating the macroscopic polarization in siesta:

1. I see that the units are given in Debye, which is a dipole moment. So is siesta really outputting the macroscopic polarization * unit cell volume? 2. From the manual, it seems like the formula used to calculate the polarization is only defined up to a quantum. Does anybody know if the output polarization are given modulo the quanta (like in abinit), or if it is not possible to tell which polarization branch they are on? I am doing a set of calculations for a particular system which does not have a well-defined reference state, so I can't use the Born charges to measure the change in polarization across my calculations. The best I can do is measure the change of the macroscopic polarization across my calculations, so I am wondering if it is guaranteed that they will be on the same branch. 3. Does anybody have advice for choosing a good polarization grid? I know I should converge my results with respect to this, but not sure what the best way to do this would be. Should I just converge the diagonal terms and then the off-diagonal terms? Any advice would be appreciated. Thanks, Daniel Bennett

-- SIESTA is supported by the Spanish Research Agency (AEI) and by the European H2020 MaX Centre of Excellence (http://www.max-centre.eu/)