Michael, Thank you for the response. I agree that I am far from the minimum. However, when I do get to the minimum, I end up with a c/a ratio that is far off, and an energy difference of 0.6 eV, about twice what you find. (I have, I believe, accounted for the proper number of atoms, etc.)
I have done the calculation with the PAW potential and the PZ-vbc potential and obtained the same results. Obviously I am doing something wrong but I simply cannot see it. I'll try the Si.pbe-n-van.UPF and see if I can reproduce your 0.29 eV energy difference. Did you c/a work out to be around 0.547? Daryl Daryl C. Chrzan Professor, Materials Science and Engineering University of California Berkeley, CA 94720 and Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 ph./fax: 510 643 1624
