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

[Amar Singh]

Hi Friends,​I am trying 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". I tried to increase the cell factor to 4, but it does not seem to work. Would be thankful for any suggestion on it. Also, curious to know that why this problem appears only when I am using ibrav = 14, and not when I am setting space group ? Thanks​Amar
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