A TDDFT study on TiO2 clusters

In this research, first principle calculations based on Time-Dependent Density Functional Theory (TDDFT) have been used to study the geometry structures, the binding energies and electronic properties of (TiO2)n clusters with n = 1/10. All possible structures of TiO2 clusters have been built, optimized and studied.
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A TDDFT study on TiO2 clustersHNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2018-0069Natural Sciences 2018, Volume 63, Issue 11, pp. 52-58This paper is available online at http://stdb.hnue.edu.vn A TDDFT STUDY ON TiO2 CLUSTERS Duong Quoc Van and Nguyen Minh Thuy Faculty of Physics, Hanoi National University of Education Abstract. In this research, first principle calculations based on Time-Dependent Density Functional Theory (TDDFT) have been used to study the geometry structures, the binding energies and electronic properties of (TiO2)n clusters with n = 1÷10. All possible structures of TiO2 clusters have been built, optimized and studied. The geometry optimization calculations indicate that almost stable structures with lowest total energies also have high symmetric shapes than the others. The calculated binding energies of stable models show that TiO 2 clusters tend to group together to form larger and more stable structures. Keywords: TiO2 clusters, TDDFT, stable structures, binding energy, electronic structures.1. Introduction TiO2 is one of the most widely used materials in science [1] and technology [2]. Recentstudies show that TiO2 nanostructures give high results in photocatalytic activity [3-7]. TiO2nanoparticles have been synthesized and applied in various regions, especial in photochemicalapplications [8]. Photocatalytic activities of TiO2 nanoparticles have been improved by differentmethods, the two most common are doping [9-11] and compositing with other materials [12, 13].To predict the photocatalytic activities of TiO2-based materials, different models of TiO2 clustershave been created, optimized and used in modified TiO2 models [14]. Xiaohui et al. [15] show that the magnetism of TiO and TiO2 clusters depend on theirshapes but the stable structures had not been discussed. Chiodo et al. [16] studied the four mostcommon types of TiO2 clusters: linear chain, ring, rutile-like and anatase-like structures but themost stable clusters have not been clearly shown. Zhang et al. [17] created the most commonstructures and studied the geometry structures, the coordinates and binding energies of (TiO 2)nclusters with n =1÷9. The compact structures are more energetically favorable than otherstructures like quasi-linear or circular ones while Blagojevic [18] showed the contrary results. The previous results do not show a clearly view on the most stable structures of TiO 2clusters and lead to the difficult in the application of calculations on modified TiO2 materials. Inthis research, all of possible structures of (TiO2)n clusters in the range of n = 1÷10 have been built,optimized, calculated to find the most stable structures for each value of n. These stable structurescan be used to create models of composite materials of TiO2.Received August 30, 2018. Revised October 12, 2018. Accepted October 19, 2018.Contact Duong Quoc Van, e-mail address: vandq@hnue.edu.vn52 A TDDFT study on TiO2 clusters2. Content2.1. Computational methods Initial TiO2 clusters have been manually built using visualization package from MaterialsStudio [19] - a commercial software widely used in modelling materials. TDDFT-basedcalculations were performed using DMol3 module [20, 21] in Materials Studio software.Generalized Gradient Approximation (GGA) were used for the exchange-correlation functionalwith the parametrization presented by Perdew, Burke and Ernzerhof (PBE) [22]. The electron-ioninteractions were modeled using norm-conserving pseudopotentials within The DensityFunctional Semi-core PseudoPotentials (DSPP) method; the valance configurations of the atomswere 3s23p63d24s2 for Ti and 2s22p4 for O. The convergence threshold for self-consistent iterationswas set at 10-6 eV. The energy change, maximum force and maximum displacement tolerances inthe geometry optimization processes were set at 10−5 Ha/atom, 0.002 Ha/Å and 0.005 Å,respectively.2.2. Results and discussion2.2.1. Structures of TiO2 clusters 1.1 2.1 2.2 2.3 3.1 3.2 3.3 3.4 4.1 4.2 4.3 4.4 4.5 4.6 5.1 5.2 5.3 5.4 Ti O 5.5 5.6 5.7 Figure 1. Initial structures of (TiO2)n clusters with n = 1÷5 In general, there are many possible structures of (TiO2)n corresponds to a certain value of n(especially for large n) but not all of them are able to exist. All initial structures of (TiO 2)n withn = 1÷5 are shown in Figure 1, total number of clusters is 21 (1 structure for n = 1; 3 structures for 53 Duong Quoc Van and Nguyen Minh Thuyn = 2; 4 structures for n = 3; 6 structures for n = 4 and 7 structures for n = 5). For n from 6 to 10,there are 32 possible structures (12 structures for n = 6; 7 structures for n = 7; 4 structures for n = 8; 6structures for n = 9 and 3 structures for n = 10). These structures are shown in Figure 2. 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 7.1 7.2 7.3 7.4 7.5 7.6 7.7 8.1 8.2 8.3 8.4 ...