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7.21 warning: 'symmetry operation # N not allowed'

This is not an error. If a symmetry operation contains a fractional translation that is incompatible with the FFT grid, it is discarded in order to prevent problems with symmetrization. Typical fractional translations are 1/2 or 1/3 of a lattice vector. If the FFT grid dimension along that direction is not divisible respectively by 2 or by 3, the symmetry operation will not transform the FFT grid into itself.



Paolo Giannozzi 2010-04-08