Density functional theory study of bulk platinum monoxide
Jamal Uddin, Juan E. Peralta, and Gustavo E. Scuseria
Department of Chemistry, Rice University, Houston, Texas 77005-1892, USA
Received 19 June 2004; revised manuscript received 2 November 2004; published 18 April 2005
The ground state electronic structure of platinum monoxide PtO has been calculated using density func-
tional theory DFT with periodic boundary conditions and Gaussian type orbitals. Several DFT exchange-
correlation functionals, including a hybrid functional based on a screened Coulomb potential for exact ex-
change have been used. Our study reveals that functionals based on the generalized gradient approximation
GGA or meta-GGA do not give qualitatively different results from those of the local spin density approxi-
mation, predicting PtO to be metallic, whereas the hybrid functional predicts a semiconductor with a band gap
of 0.86 eV. A reduced band gap of 0.56 eV is found in the oxygen deficient PtO
0.9
system.
DOI: 10.1103/PhysRevB.71.155112 PACS numbers: 71.20.-b, 71.15.Mb, 71.15.Ap
I. INTRODUCTION
PtO belongs to the technologically important group of
noble-metal monoxides that includes species like NiO and
PdO. Extensive theoretical and experimental studies have
been performed on the electronic structures of NiO and
PdO.
1–11
On the other hand, PtO has attracted far less atten-
tion primarily due to its limited applications. In recent years,
however, PtO has become the focus of interest because of its
potential use as an important technological material such
as gate electrodes in the fabrication of the next generation
of large scale integrators and dynamic random access memo-
ries DRAMs. Thin films of Pt oxides are promising candi-
dates for electrode materials in ferroelectric memory
capacitors.
12,13
A study reported that PtO can improve the
endurance properties of the ferroelectric capacitor.
14,15
The
fatigue properties of Pt oxides are better than those of any
other oxide electrodes.
16
High selectivity as well as enhanced
deposition and dielectric properties are achieved for tantalum
pentaoxide Ta
2
O
5
, used for ultradensity DRAM materials,
when the Pt electrode is replaced by PtO.
17
The latter elec-
trode provides with a rugged structure that significantly in-
creases the capacitance density of Ta
2
O
5
. PtO also plays an
important role in the oxidation-reduction processes at the
fuel cell electrodes. Studies have shown that PtO is involved
in the catalyzed dioxygen reduction to produce hydrogen
peroxide.
18
PtO has also been used in the synthesis of self-
assembled monolayers.
19
The structure and electrical properties of PtO have been a
matter of interest and controversy at the same time. The crys-
tallographic structure of PtO was predicted by Moore and
Pauling
20
in 1941, whereas Westwood and Bennewitz,
21
fol-
lowed by Hecq and Hecq,
22
reconfirmed its existence in the
thin film form.
23
Refined structural data has been published
by McBride et al. later on.
24
The crystal structure of PtO is
similar to that of PdO, with two formula units per tetragonal
unit cell in a D
4h
9
space group where the metal ions acquire
coplanar rectangular dsp
2
coordination and the anions
achieve a near tetrahedral environment.
Experimental data on the optical and electrical properties
of PtO is scarce.
24,25
Contradictory results are found in the
literature claiming PtO to be a metallic conductor and a
semiconductor. Based on scanning tunneling microscopy
STM and infrared reflectivity spectra techniques, McBride
et al.
24
concluded that PtO is a nonmagnetic p-type semicon-
ductor with conductivity = 2.25
-1
cm
-1
and free carrier
concentration n = 4.11 10
18
cm
-3
. More recently, Abe et al.
reported
25
PtO to be a metallic conductor with a resistivity of
1–2 m cm.
Only a few theoretical studies on the electronic properties
of PtO can be found in the literature. A small band gap of
0.7 eV was found for PtO by Hass and Carlsson
26
using the
augmented-spherical-waves ASW method and the local
density approximation LDA. Ahuja et al.
27
predicted PtO to
have a band gap of 0.6 eV employing the linear-muffin-tin-
orbital method in the atomic-sphere approximation LMTO-
ASA and the Barth-Hedin local exchange-correlation func-
tional. On the other hand, calculations based on all-electron
full-potential-linearized augmented plane wave FLAPW
and full-potential linear-muffin-tin-orbital FLMTO meth-
ods predicted PtO to be a metal.
28
These calculations were
carried out using LDA with the Hedin-Lundqvist exchange-
correlation functional. In light of these contradictory results,
it is relevant to carry out further investigations of PtO using
theoretical methods.
It is known that LSDA underestimates band gaps in semi-
conductors and insulators.
29,30
Such underestimation in some
cases can completely close the gap, and semiconductors are
predicted to be metals, as for instance in UO
2
.
31
Therefore,
more reliable methods are required for studying the elec-
tronic properties of bulk PtO.
Hybrid density functionals,
32
which contain a portion of
exact exchange loosely referred to as Hartree-Fock ex-
change are popular in quantum chemistry since they provide
higher accuracy than LSDA or generalized gradient approxi-
mation GGA functionals.
33
In solid state calculations, however, the use of hybrid
functionals is not a common practice because of the high
computational cost that exact exchange involves. A recent
alternative to conventional hybrid functionals is a screened
exchange hybrid functional developed by Heyd, Scuseria,
and Ernzerhof HSE.
34,35
This functional uses a screened
Coulomb potential for the exact exchange interaction, dras-
tically reducing its computational cost, and providing results
of similar quality than traditional hybrid functionals. In par-
PHYSICAL REVIEW B 71, 155112 2005
1098-0121/2005/7115/1551127/$23.00 ©2005 The American Physical Society 155112-1