to/at a=10.77A (plotting E vs a give me a nice parabola curve). I then rerun the structure at min E (i.e. a=10.77) using vc-relax. I obtained the following:
CELL_PARAMETERS (alat) 1.000000000 0.000000000 0.000000000 0.000000000 1.000000000 0.000000000 0.000000000 0.000000000 1.000000000 alat = 20.3289 au (or 10.75760138 A), E=-508.1650690 Ry Comparing to the results by scf calculations, I see the result from vc-relax and scf calculations are not consistent at all. I thought they should. However, the total stress computed for the scf calculation at min energy is still large (P = -3.36 kbar), while the stress calculated by the vc relax is small P = -0.04 kbar. I also noted that the cell size at which the system has a min stress (i.e. almost zero stress) given by scf calculations does not coincide with the cell size at which the the system has a minimum energy (min of the parabola). I thought that at the optimized cell size, both stress and energy have to be minimum. I don't understand why there is such a difference. Am I wrong in the way I was doing? Thank you very much, Trinh Vo JPL/Caltech
