We report the results of a series of
density functional theory (DFT) calculations aime
d at pre
dictingthe
57Fe M&
ouml;ssbauer electric fiel
d gra
dient (EFG) tensors (qua
drupole splittings an
d asymmetry parameters)an
d their orientations in
S = 0,
1/
2, 1,
3/
2, 2, an
d 5/
2 metalloproteins an
d/or mo
del systems. Excellent resultswere foun
d by using a Wachter's all electron basis set for iron, 6-311G* for other heavy atoms, an
d 6-31G*for hy
drogen atoms, BPW91 an
d B3LYP exchange-correlation functionals, an
d spin-unrestricte
d metho
dsfor the paramagnetic systems. For the theory versus experiment correlation, we foun
d R2 = 0.975, slope= 0.99, intercept = -0.08 mm sec
-1, rms
d = 0.30 mm sec
-1 (
N = 23 points) covering a
EQ range of 5.63mm s
-1 when using the BPW91 functional an
d R2 = 0.978, slope = 1.12, intercept = -0.26 mm sec
-1,rms
d = 0.31 mm sec
-1 when using the B3LYP functional.
EQ values in the following systems weresuccessfully pre
dicte
d: (1) ferric low-spin (
S =
1/
2) systems, inclu
ding one iron porphyrin with the usual(
dxy)
2(
dxzdyz)
3 electronic configuration an
d two iron porphyrins with the more unusual (
dxzdyz)
4(
dxy)
1 electronicconfiguration; (2) ferrous NO-heme mo
del compoun
ds (
S =
1/
2); (3) ferrous interme
diate spin (
S = 1)tetraphenylporphinato iron(II); (4) a ferric interme
diate spin (
S =
3/
2) iron porphyrin; (5) ferrous high-spin(
S = 2)
deoxymyoglobin an
d deoxyhemoglobin; an
d (6) ferric high spin (
S =
5/
2) metmyoglobin plus twofive-coor
dinate an
d one six-coor
dinate iron porphyrins. In a
ddition, seven
diamagnetic (
S = 0,
d6 an
d d8)systems stu
die
d previously were reinvestigate
d using the same functionals an
d basis set scheme as use
dfor the paramagnetic systems. All compute
d asymmetry parameters were foun
d to be in goo
d agreementwith the available experimental
data as were the electric fiel
d gra
dient tensor orientations. In a
ddition, weinvestigate
d the electronic structures of several systems, inclu
ding the (
dxy)
2(
dxz,
dyz)
3 an
d (
dxz,
dyz)
4(
dxy)
1[Fe(III)/porphyrinate]
+ cations as well as the NO a
dduct of Fe(II)(octaethylporphinate), where interestinginformation on the spin
density
distributions can be rea
dily obtaine
d from the compute
d wave functions.