Assessment of density functional theory for iron(II) molecules across the spin-crossover transition
Citation:
A. Droghetti, D. Alf? and S. Sanvito, Assessment of density functional theory for iron(II) molecules across the spin-crossover transition, Journal of Chemical Physics, 137, 12, 2012, 124303-Download Item:
Abstract:
Octahedral Fe
2
+
molecules are particularly interesting as they often exhibit a spin-crossover transi-
tion. In spite of the many efforts aimed at assessing the performances of density functional theory
for such systems, an exchange-correlation functional able to account accurately for the energetic of
the various possible spin-states has not been identified yet. Here, we critically discuss the issues
related to the theoretical description of this class of molecules from first principles. In particular,
we present a comparison between different density functionals for four ions, namely, [Fe(H
2
O)
6
]
2
+
,
[Fe(NH
3
)
6
]
2
+
, [Fe(NCH)
6
]
2
+
, and [Fe(CO)
6
]
2
+
. These are characterized by different ligand-field
splittings and ground state spin multiplicities. Since no experimental data are available for the gas
phase, the density functional theory results are benchmarked against those obtained with diffusion
Monte Carlo, one of the most accurate methods available to compute ground state total energies of
quantum systems. On the one hand, we show that most of the functionals considered provide a good
description of the geometry and of the shape of the potential energy surfaces. On the other hand, the
same functionals fail badly in predicting the energy differences between the various spin states. In the
case of [Fe(H
2
O)
6
]
2
+
, [Fe(NH
3
)
6
]
2
+
, [Fe(NCH)
6
]
2
+
, this failure is related to the drastic underestima-
tion of the exchange energy. Therefore, quite accurate results can be achieved with hybrid functionals
including about 50% of Hartree-Fock exchange. In contrast, in the case of [Fe(CO)
6
]
2
+
, the failure
is likely to be caused by the multiconfigurational character of the ground state wave-function and
no suitable exchange and correlation functional has been identified.
Sponsor
Grant Number
European Union (EU)
E12443
European Union (EU)
263104
Author's Homepage:
http://people.tcd.ie/sanvitoshttp://people.tcd.ie/droghea
Description:
PUBLISHED
Author: Sanvito, Stefano; Droghetti, Andrea
Type of material:
Journal ArticleCollections
Series/Report no:
Journal of Chemical Physics137
12
Availability:
Full text availableKeywords:
Iron MoleculesSubject (TCD):
Nanoscience & MaterialsDOI:
http://dx.doi.org/10.1063/1.4752411Metadata
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