[Re:11] Regarding afm fcc-Fe convergance and higher total energy values compared to bcc fm-Fe

Posted on : December 06, 2018 (Thu) 12:52:24

by Hitoshi GOMI

Hello Qais,

I guess your rmt value is not an optimized one, but just a touching one.
This is just a simple mathematics.

The distance between Fe1 (0 0 0) and Fe3 (0.5 0.5 0) is calculated to be d13 = sqrt(a^2 + a^2) / 2 / a = sqrt(2) / 2.
Simiraly, the distance between Fe1 and Fe2 (0.5 0 0.5c) is calculated to be d12 = sqrt(a^2 + (a * c/a)^2) / 2 / a = sqrt(1 + (c/a)^2) / 2.

If c/a = 1, d12 = d13. Therefore, the touching rmt = d12 / 2 = d13 / 2.
If c/a > 1, d12 > d13. Therefore, the touching rmt = d13 / 2.
If c/a < 1, d12 < d13. Therefore, the touching rmt = d12 / 2.

Hitoshi GOMI