I am testing the convergence of a few isolated systems and I find problems in converging systems containing very electronegative elements. I am varying ecut and acell only, pseudo is PBE and kpt is always 1.
Most of the molecules converge fine, but it becomes more difficult the more I move right in the periodic table.
BF4 and PF6 are the worst molecules, never converging.
BF3 and BCl3 show some non-converging case, but taking an high ecut (>20) and an high acell (>30) is enough.
N2 also presents some problems.
So, what is wrong with PBE+halogen atoms?
Here's an example of non converging system (BF4):
Code: Select all
#Definition of the unit cell
acell 3*30
#Definition of the atom types
ntypat 2
znucl 5 9
#Definition of the atoms
natom 5
typat 1 2 2 2 2
xcart
0.0001148660 0.0000001274 0.0000948037
0.0000254663 0.0000002928 1.4168343567
1.3357270137 0.0000003076 -0.4722566817
-0.6679098939 -1.1565412448 -0.4723165605
-0.6679091494 1.1565405706 -0.4723160520
#Definition of the planewave basis set
ecut 30
#Definition of the k-point grid
kptopt 0 # Enter the k points manually
nkpt 1 # Only one k point is needed for isolated system,
kpt 0.0 0.0 0.0 # taken by default to be 0.0 0.0 0.0
#Definition of the SCF procedure
nstep 300 # Maximal number of SCF cycles
toldfe 1.0d-6
diemac 2.0