mm/s, a PBE = −0.310(25) a.u.
3 mm/s. The similar values were also obtained by
Wdowik [17] (−0.291 a.u.
3 mm/s) and Kurian [22] (–0.31 a.u.
3 mm/s). However, the
isomer shift calibration constant values varied from −0.11 to −0.62 a.u.
3 mm/s [17].
In a similar way, the quadrupole split based on ab initio calculations can be
estimated. The experimental quadrupole splitting parameter (QS) can be expressed
as [2]:
QS ¼
eQ
2
V zz 1 þ
1
3
g
2
1=2
ð9:8Þ
Table 9.1 Isomer shift values and the calculated q 0 values for different exchange-correlation
potentials for the calibration compounds
Compound
IS exp (mm/s)
q 0
LDA (a.u.
−3
)
q 0
LDA (a.u.
−3
)
q 0
PBEsol (a.u.
−3
)
TiFe
–0.145
15,223.03976
15,310.50415
15,276.26512
C-Fe
–0.100
15,222.73036
15,310.20858
15,275.97564
a-Fe
0.000
15,222.33304
15,309.80079
15,275.56425
Fe 2 O 3
0.370
15,220.52611
15,308.07181
15,273.83556
FeF 3
0.489
15,220.08541
15,307.60416
15,273.34467
FeCl 3
0.530
15,220.18412
15,307.68599
15,273.44398
FeO
0.810
15,218.85291
15,306.29004
15,272.09560
FeI 2
1.044
15,218.88889
15,306.39925
15,272.11893
FeTiO 3
1.070
15,219.01978
15,306.43586
15,272.23207
FeCl 2
1.092
15,218.76946
15,306.25103
15,272.00249
FeBr 2
1.120
15,218.80125
15,306.30642
15,272.03606
FeF 2
1.467
15,218.21831
15,305.73292
15,271.46350
Fig. 9.3 Experimental
isomer shift plotted versus the
difference in electron density
for various compounds
282
P. Stoch and A. Stoch