ABINIT Discussion Forums

Hello,
i wana to calculate piezoelectric constant so i studied its tutorial and now i use tfield_2 in abinit. i have an error. would you please guide me?
my Input file:
acell 3*6.20 angstrom
angdeg 60 60 60
spgroup 161
spgaxor 2
natrd 3
natom 10
xred 0.000000000 0.000000000 0.000000000
0.231000006 0.231000006 0.231000006
0.398999989 0.541000009 0.945999980
ntypat 3
typat 1 1 2 2 3 3 3 3 3 3
znucl 26 22 8
ixc 3
iscf 5
nstep 100
ecut 25
ecutsm 0.5
dilatmx 1.05
ngkpt 6 6 6
nshiftk 1
shiftk 0.5 0.5 0.5
ndtset 3
prtden1 1
kptopt1 1
toldfe1 1.0d-12
getden2 1
kptopt2 2
iscf2 -2
getwfk2 1
tolwfr2 1.0d-22
nband2 50
berryopt2 -2
rfdir2 1 1 1
getwfk3 2
getddk3 2
rfdir3 1 1 1
rfstrs3 3
rfphon3 1
rfatpol3 1 2
toldfe3 1.0d-12
nband3 50
kptopt3 2
My ERROR:
occeig : ERROR -
In a non-metallic case (occopt<3), for a RF calculation,
if the eigenvalues are degenerate, the occupation numbers must also be degenerate.
However, the following pair of states gave :
k -state, band number 28, occ= 2.000000E+00, eigenvalue= -2.579708E-01,
kq-state, band number 29, occ= 0.000000E+00, eigenvalue= -2.579708E-01.
Action : change occopt, consistently, in GS and RF calculations.
Best regards.

Hi,

It might be that LDA (ixc 3) finds your material metallic. However, values of occopt others than 1 aren't allowed with berryopt -2, meaning that your system HAS to be semiconducting if your are to carry out your calculation.

First, could you check the eigenvalues of your system resulting from the ground state calculation (your dataset 1) and see if it is indeed metallic? If it is, and it is known experimentally not to be metallic, then the easy solution would be to change your functional (the value if ixc) so that ground state calculations find your material semiconducting. You could try, for starter, to use ixc 11 (PBE functional) in such a situation.

Good luck,

Jonathan

Hello,
Thank you Jolafc,I wana to know can i do this calculations (piezoelectric calculation) with LDA+U approximation with abinit-6.0.4?
Best regards.
Mina.

Hi,
I am having the same problem for graphane phonons:

ITER STEP NUMBER 1
-P-0000 occeig : ERROR -
-P-0000 In a non-metallic case (occopt<3), for a RF calculation,
-P-0000 if the eigenvalues are degenerate, the occupation numbers must also be degenerate.
-P-0000 However, the following pair of states gave :
-P-0000 k -state, band number 5, occ= 2.000000E+00, eigenvalue= -6.001412E-02,
-P-0000 kq-state, band number 6, occ= 0.000000E+00, eigenvalue= -6.001412E-02.
-P-0000 Action : change occopt, consistently, in GS and RF calculations.
-P-0000
-P-0000 leave_new : decision taken to exit ...

grapahane is a wide gap semiconductor and I have to use occopt 1.

Thanks,
Samir