I'm currently running a simulation of a single silicon impurity in gallium arsenide. I know the level introduced to the band structure from the impurity should be quite close to the conduction band edge, however I'm running into problems when it comes to including the spin polarization of the system. The silicon atom replaces a gallium, and so the system has an odd number of electrons. This causes a splitting of the electron states because of the in-balance in the number of spin up and spin down occupied states. The splitting for most of the states is on the order of a few meV, however for the impurity band gap state the splitting is around 400meV
state,energy(eV)
112 0
112 0.00383
113 0.0725
113 0.53257
114 0.73192
114 0.78767
State 112 is the top of the valence bands, 114 is the bottom of the conduction bands and state 113 is the silicon band gap state.
When I run the simulation with an extra electron (using charge=-1) the non-degeneracy is removed and I get
state,energy(eV)
112 0
112 0
113 0.5749
113 0.5749
114 0.74217
114 0.74217
Can anyone shed any light on what may be the cause of this strange low energy state (0.0725 eV)/large splitting for the spin polarized case? Or even provide any information on how abinit calculates the energies of half occupies sates (I assume it randomly picks a spin direction, but I only assumed this because I didn't think there'd be such a large difference between spin up and spin down).
Thanks in advance,
Freddie
This is the code I use to generate the ground state density:
Code: Select all
ndtset 1
chksymbreak 0
chkprim 0
nsppol 2
kptopt1 1
nshiftk1 2
shiftk1 0.5 0.0 0.0
0.0 0.5 0.0
ngkpt1 2 2 1
prtden1 1
prtpot1 1
prtvha1 1
prtvhxc1 1
prtvxc1 1
toldfe1 3.67d-6 #Hartrees (0.1meV)
#Definition of the unit cell
acell *5.53 angstrom
rprim sqrt(2) 0.0 0.0
0.0 2.0 0.0
0.0 0.0 sqrt(169/8)
#Definition of the atom types
ntypat 3
znucl 31 33 14
#Definition of the atoms
natom 56
typat 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1
2 2 2 2 2 2 2 2 2 2
2 2 2 2 2 2 2 2 2 2
2 2 2 2 2 2 2 2
xangst
0.000000000 -0.385526610 0.454466800
0.000000000 0.012010490 3.933294720
0.000000000 0.011987300 7.797602650
0.000000000 -0.385459350 11.276466050
3.910300500 -0.385526610 0.454466800
3.910300500 0.012010490 3.933294720
3.910300500 0.011987300 7.797602650
3.910300500 -0.385459350 11.276466050
0.000000000 5.144473390 0.454466800
0.000000000 5.542010490 3.933294720
0.000000000 5.541987300 7.797602650
0.000000000 5.144540650 11.276466050
3.910300500 5.144473390 0.454466800
3.910300500 5.542010490 3.933294720
3.910300500 5.541987300 7.797602650
3.910300500 5.368131014 11.568308548
1.955150000 2.805311474 1.955150000
1.955150000 2.765000000 5.865451000
1.955150000 2.808548880 9.853081290
5.865450500 2.805311474 1.955150000
5.865450500 2.765000000 5.865451000
5.865450500 2.808548880 9.853081290
1.955150000 8.335311474 1.955150000
1.955150000 8.295000000 5.865451000
1.955150000 8.338548880 9.853081290
5.865450500 8.335311474 1.955150000
5.865450500 8.295000000 5.865451000
5.865450500 8.338548880 9.853081290
0.000000000 1.421231090 1.979824640
0.000000000 1.382500000 5.865451000
0.000000000 1.421226650 9.751056610
3.910300500 1.421231090 1.979824640
3.910300500 1.382500000 5.865451000
3.910300500 1.421226650 9.751056610
0.000000000 6.951231090 1.979824640
0.000000000 6.912500000 5.865451000
0.000000000 6.951226650 9.751056610
3.910300500 6.951231090 1.979824640
3.910300500 6.912500000 5.865451000
3.910300500 6.951226650 9.751056610
1.955150000 3.989964780 -0.222282780
1.955150000 4.142950030 3.884579150
1.955150000 4.142948400 7.846299400
1.955150000 3.989956370 11.953178360
5.865450500 3.989964780 -0.222282780
5.865450500 4.142950030 3.884579150
5.865450500 4.142948400 7.846299400
5.865450500 3.989956370 11.953178360
1.955150000 9.519964780 -0.222282780
1.955150000 9.672950030 3.884579150
1.955150000 9.672948400 7.846299400
1.955150000 9.519956370 11.953178360
5.865450500 9.519964780 -0.222282780
5.865450500 9.672950030 3.884579150
5.865450500 9.672948400 7.846299400
5.865450500 9.519956370 11.953178360
#Definition of the planewave basis set
ecut 10.0
#Definition of the SCF procedure
nstep 100
diemac 10.0
diemix 0.33
And this is the code to calculate the eigenvalues at gamma:
Code: Select all
ndtset 1
chksymbreak 0
chkprim 0
nsppol 2
iscf -2
kptopt 0
irdden 1
nband 224
nbdbuf 102
nkpt 1
kpt 0.0 0.0 0.0 # G
enunit 1
tolwfr 1.0d-12
#Definition of the unit cell
acell *5.53 angstrom
rprim sqrt(2) 0.0 0.0
0.0 2.0 0.0
0.0 0.0 sqrt(169/8)
#Definition of the atom types
ntypat 3
znucl 31 33 14
#Definition of the atoms
natom 56
typat 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 3 1 1 1 1
1 1 1 1 1 1 1 1
2 2 2 2 2 2 2 2 2 2
2 2 2 2 2 2 2 2 2 2
2 2 2 2 2 2 2 2
xangst
0.0000000000E+00 -3.8552661000E-01 4.5446680000E-01
0.0000000000E+00 1.2010490000E-02 3.9332947200E+00
0.0000000000E+00 1.1987300000E-02 7.7976026500E+00
0.0000000000E+00 -3.8545935000E-01 1.1276466050E+01
3.9103005000E+00 -3.8552661000E-01 4.5446680000E-01
3.9103005000E+00 1.2010490000E-02 3.9332947200E+00
3.9103005000E+00 1.1987300000E-02 7.7976026500E+00
3.9103005000E+00 -3.8545935000E-01 1.1276466050E+01
0.0000000000E+00 5.1444733900E+00 4.5446680000E-01
0.0000000000E+00 5.5420104900E+00 3.9332947200E+00
0.0000000000E+00 5.5419873000E+00 7.7976026500E+00
0.0000000000E+00 5.1445406500E+00 1.1276466050E+01
3.9103005000E+00 5.1444733900E+00 4.5446680000E-01
3.9103005000E+00 5.5420104900E+00 3.9332947200E+00
3.9103005000E+00 5.5419873000E+00 7.7976026500E+00
3.9103005000E+00 5.3681310140E+00 1.1568308548E+01
1.9551500000E+00 2.8053114740E+00 1.9551500000E+00
1.9551500000E+00 2.7650000000E+00 5.8654510000E+00
1.9551500000E+00 2.8085488800E+00 9.8530812900E+00
5.8654505000E+00 2.8053114740E+00 1.9551500000E+00
5.8654505000E+00 2.7650000000E+00 5.8654510000E+00
5.8654505000E+00 2.8085488800E+00 9.8530812900E+00
1.9551500000E+00 8.3353114740E+00 1.9551500000E+00
1.9551500000E+00 8.2950000000E+00 5.8654510000E+00
1.9551500000E+00 8.3385488800E+00 9.8530812900E+00
5.8654505000E+00 8.3353114740E+00 1.9551500000E+00
5.8654505000E+00 8.2950000000E+00 5.8654510000E+00
5.8654505000E+00 8.3385488800E+00 9.8530812900E+00
0.0000000000E+00 1.4212310900E+00 1.9798246400E+00
0.0000000000E+00 1.3825000000E+00 5.8654510000E+00
0.0000000000E+00 1.4212266500E+00 9.7510566100E+00
3.9103005000E+00 1.4212310900E+00 1.9798246400E+00
3.9103005000E+00 1.3825000000E+00 5.8654510000E+00
3.9103005000E+00 1.4212266500E+00 9.7510566100E+00
0.0000000000E+00 6.9512310900E+00 1.9798246400E+00
0.0000000000E+00 6.9125000000E+00 5.8654510000E+00
0.0000000000E+00 6.9512266500E+00 9.7510566100E+00
3.9103005000E+00 6.9512310900E+00 1.9798246400E+00
3.9103005000E+00 6.9125000000E+00 5.8654510000E+00
3.9103005000E+00 6.9512266500E+00 9.7510566100E+00
1.9551500000E+00 3.9899647800E+00 -2.2228278000E-01
1.9551500000E+00 4.1429500300E+00 3.8845791500E+00
1.9551500000E+00 4.1429484000E+00 7.8462994000E+00
1.9551500000E+00 3.9899563700E+00 1.1953178360E+01
5.8654505000E+00 3.9899647800E+00 -2.2228278000E-01
5.8654505000E+00 4.1429500300E+00 3.8845791500E+00
5.8654505000E+00 4.1429484000E+00 7.8462994000E+00
5.8654505000E+00 3.9899563700E+00 1.1953178360E+01
1.9551500000E+00 9.5199647800E+00 -2.2228278000E-01
1.9551500000E+00 9.6729500300E+00 3.8845791500E+00
1.9551500000E+00 9.6729484000E+00 7.8462994000E+00
1.9551500000E+00 9.5199563700E+00 1.1953178360E+01
5.8654505000E+00 9.5199647800E+00 -2.2228278000E-01
5.8654505000E+00 9.6729500300E+00 3.8845791500E+00
5.8654505000E+00 9.6729484000E+00 7.8462994000E+00
5.8654505000E+00 9.5199563700E+00 1.1953178360E+01
#Definition of the planewave basis set
ecut 10.0
#Definition of the SCF procedure
nstep 100
diemac 10.0
diemix 0.33