[Pw_forum] Contracting cell volume for supercell in vc-relax

[Amar Singh]

Hi Friends,​I am tryin to optimize a supercell using vc-relax. In a first step, I used the space group to optimize one unit cell which gives a reasonable cell volume. Later, when I tried using same unit cell to optimize a supercell using ibrav = 14, unit cell volume keeps on shrinking and finally ends up with an error "Not enough space allocated for radial FFT: try restarting with a larger cell_factor". On pwscf forum I found that this error can be taken care by setting cell_dofree. ​I am curious to know that why this problem appears only when I am using ibrav = 14, and not when I am setting space group ? Would it make sense, if I cell_dofree = 'shape' for supercell optimization.Thanks​Amar
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