I'm optimizing surface of a material with norm-conserving PP. My ecut value is 50Ry, so because I'm using norm-conserving PP my ecutrho should be 200Ry. Meanwhile, because I calculate surface, there 10A of vacuum in [001] direction. Then I need optimization of ecutrho value. But when I tried to make a graph of total energy vs ecutrho, then I see that my energy does not converge. For values, the 200-400Ry total energy is about -1520 Ry, for 450-550Ry, is -1393Ry.
Why does such large difference appear? And which ecutrho value I should choose?
Dear
first of all, depending on the used material, i think that a value of Ecut=50 Ry is not suffiicent for Norm conserving PP, thus you need to test convergence versus ecut before ecutrho. when you get the optimised value of Ecut, you can use Ecutrho=4*Ecut and generally this work fine. you shouls also test convergence versus the K point mesh. this is very important. after get all optimised values for you bulk material, you can go to test convergence on the surface slab model.
best regards
same to Mr Mohamed Ali Lahmer, a ranther bigger Ecut is recommed when you are using NCPP popentials. So... why do not use PAW potentials?,,,,,,
Mohamed Ali Lahmer, thank you for the answer. I will try to use bigger value of ecut (60-70 Ry).
- Badges
- Science topic
- Similar topics
- Biological Science
- Physiology
- Physiological Processes
- Stress