Dear QE users and Developers, I'm working with NMR calculations in Gipaw. Recently I did some shielding calculations and I have some questions regarding the magnetic susceptibility. The article from developers Mauri et al (*PRL 77, 26, 1996*) explain that the shielding of a bulk of a periodic system is also periodic (i.e. has the same periodicity of *G*, the reciprocal lattice vectors), and it is proportional to the magnetic susceptibility matrix. In the paper Mauri did a short discussion about the macroscopic susceptibility, which is calculated at *G=0*. Follow my questions:
i) Assuming that the macroscopic susceptibility is calculating at gamma point (*G=0*) and depends of the sample's shape, Does make sense to do a NMR calculation with automatic kpoints (monkhorst pack grid) that does not include the gamma point? It is mandatory to including the gamma point when the shape correction is .true.? ii) Does the susceptibility depends of the supercell size? I found very different susceptibilities for the same material (AB graphite) changing the supercell size. iii) Why the susceptibility matrix is not diagonal when the shape correction is .true.? Assuming the Mauri paper I think it doens't make sense. Help me to understand... I appreciate any help, Thanks in advance, Alan. -- Alan J. Romanel Ambrozio Bacharel em Física Mestre em Eng. de Materiais Doutorando em Física - PPGFis
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