Thank you for your reply Sir. I really appreciate it.
Yes i have tried it by swap the coordinate system axes and then click Y <-> Z. It turned out as attached. But Sir, i still dont understand because the direction of x, y, and z-axes that I circle as in the picture attached doesn't change.
Also Sir, can you explain me what does it mean from my questions 1 and 2 above. Do I need to set it in the optimize geometry or it has something to do with Coordinate tools > quick optimizer ? while for vacuum, do i need to set it in lattice parameter ?