Defining a simple cubic unit cell
Posted: Wed Sep 09, 2015 2:40 pm
Interestingly, I'm having difficulty understanding how to write input for a simple cubic cell. When I do structural optimization for CsI I get a lattice constant of 6.0 bohr, which, taking into account the slight underestimation of LDA, is sqrt(2) times smaller than the experimental value of 8.629 (4.566 A). Is it possible that a factor of sqrt(2) is related to conversion from the conventional to the primitive cell? I thought for a simple cubic cell these were the same.
Code: Select all
# CsI, HGH PPs taken from Abinit website
ndtset 7
acell1 3*5.7
acell1 3*5.8
acell2 3*5.9
acell3 3*6.0
acell4 3*6.1
acell5 3*6.2
acell6 3*6.3
acell7 3*6.4
rprim
1 0 0
0 1 0
0 0 1
ntypat 2
znucl 55 53
natom 2
typat 1 2
xred 3*0.0 3*0.5
ngkpt 3*8
shiftk 3*0.0
nband 6
nbdbuf 2
ecut 60
tolvrs 1d-9
diemac 5.6