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I have a question regarding the ISIF tag. I am confused with the way that the table for the ISIF tag reads. For example, ISIF = 3 will relax the cell volume, the shape and the ions. For ISIF = 2 the ions are relaxed, but the cell volume and shape remain unchanged. If the ions are relaxed, won't the cell volume and shape inherently relax to a different shape/volume if the equilibrium shape and volume are different from that specified? Similarly, ISIF = 6, how can the cell shape and volume change if the ions are not allowed to relax. And finally, ISIF = 7, if the cell shape and the ions are not allowed to relax, how and why would the cell volume change?

the cell volume needs not necessarily change it the ions relax (or it even has to be kept fixed for good reason)
also, the cell volume can change without moving the ions if the volume itself is not at its equilibrium (wrong input lattice constants, V-depencence on the chosen XC functional,...)