My Community

If PSTRESS is used, the external pressure is applied uniformly to the cell, isn't it? How to add axial pressure or stress then?
thanks

via setting PSTRESS only hydrostatic pressure can be applied, you are right. There is no automatic way to do axial pressure, you have to do a series of calculations with different cell volumes (and shapes) do model that

can I do an axial volume change, say, between -1.0% to 1.0% at a step of 0.01% along z axis? But when I relax the system at each stage, the volume should be fixed and only ions are allowed to move right?

For this calculations you should have a look at:
http://cms.mpi.univie.ac.at/vasp/vasp/node103.html
and see how to fix select the proper ISIF.

When they systems is being relaxed at different values of the lattice constant along the z axis, (namely different volume) shall I allow shape chage at ? Or no shape change? I am going to calculate z axial strain energy, if I change the shape, will it still be a z axial strain? Thanks

When they systems is being relaxed at different values of the lattice constant along the z axis, (namely different volume) shall I allow shape chage at ? Or no shape change? I am going to calculate z axial strain energy, if I change the shape, will it still be a z axial strain? Thanks

This depends on the experiments you compare with:
1) the ions have to be relaxed.
2) V, shape:
As soon as either V or the shape are free to relax, they relax to the minimum force (energy) configuration of the respective (hydrostatic) pressure (V fixed) or adapt the equilibrium V (shape fixed) . If you allow for a shape change, all lattice parameters are adjusted (you cannot fix c and allow for a shape change automatically)