Ab initio study of neutral ( TiO2 ) n clusters and their interactions with water and transition metal atoms
Author
Çakır, D.
Gülseren, O.
Date
2012-07-04Source Title
Journal of Physics: Condensed Matter
Print ISSN
0953-8984
Publisher
IOP Publishing
Volume
24
Issue
30
Pages
305301-1 - 305301-13
Language
English
Type
ArticleItem Usage Stats
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Abstract
We have systematically investigated the growth behavior and stability of small stoichiometric (TiO2)n
(n = 1–10) clusters as well as their structural, electronic and magnetic properties by using the
first-principles plane wave pseudopotential method within density functional theory. In order to find out
the ground state geometries, a large number of initial cluster structures for each n has been searched via
total energy calculations. Generally, the ground state structures for the case of n = 1–9 clusters have at
least one monovalent O atom, which only binds to a single Ti atom. However, the most stable structure of
the n = 10 cluster does not have any monovalent O atom. On the other hand, Ti atoms are at least
fourfold coordinated for the ground state structures for n ≥ 4 clusters. Our calculations have revealed
that clusters prefer to form three-dimensional structures. Furthermore, all these stoichiometric clusters
have nonmagnetic ground state. The formation energy and the highest occupied molecular orbital
(HOMO)–lowest unoccupied molecular orbital (LUMO) gap for the most stable structure of (TiO2)n
clusters for each n have also been calculated. The formation energy and hence the stability increases as
the cluster size grows. In addition, the interactions between the ground state structure of the (TiO2)n
cluster and a single water molecule have been studied. The binding energy (Eb) of the H2O molecule
exhibits an oscillatory behavior with the size of the clusters. A single water molecule preferably binds to
the cluster Ti atom through its oxygen atom, resulting an average binding energy of 1.1 eV. We have also
reported the interaction of the selected clusters (n = 3, 4, 10) with multiple water molecules. We have
found that additional water molecules lead to a decrease in the binding energy of these molecules to the
(TiO2)n clusters. Finally, the adsorption of transition metal (TM) atoms (V, Co and Pt) on the n = 10
cluster has been investigated for possible functionalization. All these elements interact strongly with this
cluster, and a permanent magnetic moment is induced upon adsorption of Co and V atoms. We have
observed gap localized TM states leading to significant HOMO–LUMO gap narrowing, which is
essential to achieve visible light response for the efficient use of TiO2 based materials. In this way,
electronic and optical as well as magnetic properties of TiO2 materials can be modulated by using the
appropriate adsorbate atoms