I found the only parameter related to pressure is Pstress tag in VASP. But the pressure of Pstress tag is Hydrostatic pressure, while I only want to put stress along z-axis. Could you please help me with this problem? Any advice will be highly appreciated! Thanks!
If the stress tensor is calculated by setting ISIF appropriately, then you can read the stress from the OUTCAR. There is no way to apply an axial stress from tags, however you can do a geometry optimization to 0 stress, then manually stress the cell in the Z direction by modifying the cell. You will need to do this for multiple volumes then fit a relationship between volume to stress and determine the volume needed for your desired stress.