Keywords : DFT

Investigation of Doped Titanium Dioxide in Anatase Phase. Study ab initio using Density Functional Theory

Paulo José Pereira de Oliveira; Fabielle Castelan Marques; Arlan da Silva Gonçalves; Greice Kelly dos Santos Brito; Enzo Victorio Andrade; Marcos Pedro Dalmaso Pinto

Advanced Materials Letters, 2020, Volume 11, Issue 1, Pages 1-5
DOI: 10.5185/amlett.2020.011459

Global warming has generated great concern worldwide. One way to control this problem is to use clean renewable energy new sources. Among the energy sources, we can mention hydrogen gas, produced by water photocatalysis by mean of a semiconductor material. In this work, we report a study about band gap and absorption spectra by mean of the density functional theory of the anatase allotropic form of titanium dioxide doped with Ruthenium. The results indicated systematic decrease of the band gap and increase of the absorbance at the visible region with the increase of the amount of dopant.

Graphene and doped graphene: A comparative DFT study

Jyoti Tyagi; Lekha Sharma; Rita Kakkar

Advanced Materials Letters, 2019, Volume 10, Issue 7, Pages 484-490
DOI: 10.5185/amlett.2019.2168

Two different models, ovalene (C32H14) and circumcoronene (C54H18) and their respective doped models (C31XH14, C53XH18 where X = B, Al, N, P, Fe, Ni and Pt) have been considered for DFT calculations at the GGA-PBE/DNP level. The two models are compared on the basis of various calculated structural parameters and electronic properties. Electronic density of states (DOS) spectra are also plotted to see the changes in the electronic properties on increasing the size. No major changes are observed in the structural and electronic properties as one move from the smaller model to the higher one. It is found that doping maintains the planarity of the surface but induces comparatively large changes in the bond lengths around the doped atom, weakening the bonds. Copyright © VBRI Press.

Synthesis, characterizations, and comparative study of electro-optical properties of indole-based squaraine sensitizers as efficiency to enhancing dye-sensitized solar cells

Sultan A. Al-horaibi; S.T. Gaikwad; Anjali S. Rajbhoj

Advanced Materials Letters, 2018, Volume 9, Issue 4, Pages 275-283
DOI: 10.5185/amlett.2018.1457

Squaraine dyes (SQ) have acquired sufficiently great attention as dye-sensitized solar cell (DSSCs) materials. In the present study, we have synthesized and characterized of two novel symmetrical sensitizers dyes for dye-sensitized solar cells which contain electron withdrawing (−COOH) group with long alkyl ester chain (SQ1) and another without encoring group (SQ2). We have investigated the structural, electronic, photo-electrochemical, and charge transport properties of two SQ1& SQ2 indole-based squaraine dyes. The ground state geometry has been computed by applying density functional theory (DFT). The excitation energy and the oscillator strength were calculated by using time-dependent (DFT-TD) at DFT/B3LYP/6-31G** level of theory. We have focused and study on the frontier molecular orbitals (HOMO and LUMO), electron injection (ΔG inject ), light harvesting efficiency (LHE), open-circuit voltage (Voc), relative electron injection (ΔGr inject ), and short-circuit current density (Jsc). The effect of-COOH as (acceptor) and -OCH3 (donor) groups on SQ1 and SQ2 were investigated. The factors affecting, ΔG inject , LHE, Voc and Jsc revealed that SQ1 would be more favourable to enhance the performance of DSSCs. The theoretical calculations and absorbance results show that the electron density of LUMO of SQ1 is delocalized in the whole chromophore, leading to strong electronic coupling between SQ1 and TiO2 surface. So, the SQ1 sensitized solar cells exhibit better photovoltaic performance. 

Effect Of Phases On The Energetics Of Pristine InP Nanowires: An Ab-initio Approach 

Pankaj Srivastava; Avaneesh Kumar; Neeraj K. Jaiswal; Varun Sharma

Advanced Materials Letters, 2016, Volume 7, Issue 10, Pages 831-835
DOI: 10.5185/amlett.2016.6240

We have investigated the electronic and structural properties of pristine Zinc-blende type InP nanowires (NWs) by using ab-initio approach. We have considered the effect of phases by taking NWs of 7 Å radii in three phases viz. (100), (110), (111). It is revealed that the electronic properties of NWs are highly affected by the wire phases. NW in (100) phase is found to be semiconducting with an indirect band gap of 0.71 eV whereas it becomes semi-metallic and metallic in other two phases. Thus, the nature of nanowires is observed as a function of NW phases. Further, energetic feasibility of InP NWs strongly dependent on their growth phase.

Theoretical Survey Of Luminescence Observed In Nanostructured Silicon Rich Oxide Films Attributed To annealing Processes

Advanced Materials Letters, 2016, Volume 7, Issue 6, Pages 480-484
DOI: 10.5185/amlett.2016.6312

The motivation of this work is to apply a new model, which we had called the Global Reactions Model (GRM), for the theoretical study of the optical and electronics properties of Silicon Rich Oxides (SRO) structures regardless of the technique used to fabricate such structures. Recently we published the Global Reactions Model (GRM) to describe a set of chemical reactions that could hypothetically occur during the process of obtaining silicon rich oxide (SRO) films, notwithstanding of the technique used to grow such films. Particularly, chemical reactions that occur during the process of growing of SRO films by Low Pressure Chemical Vapor Deposition (LPCVD) and Hot Filament Chemical Vapor Deposition (HFCVD) techniques were emphasized in these models. We suggest and evaluate either some types of molecules or resulting nanostructures and we have predicted theoretically, by applying the density functional theory (DFT), the contribution that they may have to the phenomenon of luminescence. We calculated the luminescent spectra of the as grown and the annealed structures. In this work we focused in siloxanes species presumably found in SRO. 

A First-principle Study Of The Optical Properties Of Pure And Doped LaNiO3

Tarun Kumar Kundu; Debolina Misra

Advanced Materials Letters, 2016, Volume 7, Issue 5, Pages 344-348
DOI: 10.5185/amlett.2016.6105

Density Functional Theory (DFT) is employed to study the various optical properties of pseudo-cubic LaNiO3. As LaNiO3 is a strongly correlated material, conventional DFT like LDA or GGA and even GW approximation fail to describe, we have examined the optical spectra of this compound using GGA(PBE)+U approach. The advantage of incorporating Hubbard U in this approach is to take the strong electronic correlation in the system into account. The optical spectra of this compound are found to be consisted of the Drude peak and some high energy peaks. While the Drude peak reflects the dominant free carrier contributions at the low energy region, the high energy peaks originate from the inter-band transitions within the system. We have also studied the remarkable changes in the optical properties in Fe doped LaNiO3 (LaNi1-xFexO3), in order to probe related properties, corresponding to their applications in solid-oxide fuel cells. Our calculations have revealed that even 25% of Fe doping is adequate to trigger a first order metal to insulator transition in LaNiO3. The optical spectra of LaNi1-xFexO3 compounds are calculated using the hybrid functional HSE and the doping-induced metal to insulator transition in LaNiO3 is attributed to the altered crystal environment and electronic configuration of the compound. 

 A Computational Investigation Of Oxygen Reduction Reaction Mechanisms On Si- And Al-doped Graphene: A Comparative Study

Mehdi D. Esrafili; Parisa Nematollahi

Advanced Materials Letters, 2015, Volume 6, Issue 6, Pages 527-530
DOI: 10.5185/amlett.2015.5751

In this letter, the mechanisms of the oxygen reduction reaction (ORR) on Si- and Al-doped graphene have been investigated to understand the effect of doped graphene on the ORR and predict details of ORR pathways. Density functional theory (DFT) calculations were used to achieve the true mechanism pathways of ORR on the surfaces. Also, free energy diagrams for the ORR were constructed to provide the stability of possible intermediates in the electrochemical reaction pathways. At first stage, the adsorption of O2 molecule on both surfaces was studied with two possible configurations: atop (most stable) and bridge with the Eads of -60.6 and -72.4 kcal/mol, while for bridge site they were about -48.9 and -60.4 kcal/mol, respectively. Then, the most stable configuration (atop) was selected and the pathways formed after the adsorption of four atomic hydrogen to O2 molecule for both surfaces. These mechanisms were similar in both Si- and Al- doped graphene but there was a little difference in the obtained intermediates formed in each surface. In each pathway, the O2 dissociation reaction was neglected because it was unlikely to occur due to the high activation energy (> 45 kcal/mol). The results of this study show an easy and economic way to obtain Si- and Al-doped graphene as a non-metal catalyst for ORR at the cathode electrode in fuel cells.  

Quantum Chemical Studies Of Nitrogen Substitution On ZnO Nanoclusters Stability

S. Sriram; R. Chandiramouli; A. Thayumanavan

Advanced Materials Letters, 2015, Volume 6, Issue 5, Pages 446-451
DOI: 10.5185/amlett.2015.5786

Importance of p-type transparent conducting oxide (TCO) is much needed in the optoelectronics industry. Due to lack of intrinsic p-type TCO, it is necessary to design or tune the properties existing n-type TCO are very essential. This present work describes, n-type ZnO is tuned to p-type by doping of nitrogen on to the nanocluster. The structural stability of ZnxOx-1N for x=(2-5) is optimized using Gaussian 09 program package with a B3LYP/6-31G level basis set. The optimization result shows that when the cluster size increases the stability also increases. The dipole moment depends on the structure of the ZnxOx-1N cluster. These optimized structural geometries are used to calculate the binding energy, HOMO-LUMO energy gap, ionization potential and electron affinity of nanoclusters. The binding energy for ring structures is found to be more than the other two structures. Vibrational analysis is carried out for all the structures and reported. The ring structure is found to be more stable than the linear and 3D structures. The findings of the present work will provide an insight to synthesis, p-type ZnO nanoclusters.

Theoretical Study Of The Geometric, Electronic Structure And Properties Of Alternating Donor-acceptor Conjugated Oligomers: Carbazole (Cbz)-based 3,4-ethylenedioxythiophene (Edot)

Z. El Malki; M. Haddad;M. Bouachrine; M. Hamidi; J-P Lere-Porte; F. Serein-Spirau; L. Bejjit

Advanced Materials Letters, 2012, Volume 3, Issue 4, Pages 266-272
DOI: 10.5185/amlett.2011.8292

In this work the geometrical and electronic properties of (Carbazole-3.4-Ethylenedioxythiophene) (Cbz-Edot) based alternating donor-acceptor conjugated oligomers were studied by the density functional theory (DFT) at the B3LYP level with 6-31G(d) basis set. The acceptors investigated include thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT) and thiadiazolothienopyrazine (TPD). A low band gap will be expected in polymers containing donor-acceptor (D-A) repeating units. In order to predict the band gaps for guiding the synthesis of novel materials with low band gaps, we apply quantum-chemical techniques to calculate the band gaps in several oligomers. The results have been compared with those of thiophene and 3,4-ethylenedioxythiophene polymers with donor-acceptor fragment. The lowest excitation energies (Eex) and the maximal absorption wavelength (λabs) are studied using the time dependent density functional theory (TD-DFT), method. The electronic transitions of the absorption spectrum derived by TD-DFT method give useful structural and electronic information for designing novel conducting organic polymer materials. The theoretical results suggest that both the acceptor strength and the stable geometry contribute significantly to the electronic properties of alternating donor-acceptor conjugated copolymers.

A Quantum Chemical Study On Structural And Electronic Properties Of New Pi-conjugated Polymer Named Poly(4-methylthioazole-2,5-diyl)

M. Amine; M. Hamidi; S.M. Bouzzine; A. Amine; M. Bouachrine

Advanced Materials Letters, 2012, Volume 3, Issue 1, Pages 15-20
DOI: 10.5185/amlett.2011.6274

Organic conjugated polymers based on heterocylic ring exhibit semiconducting properties associated with the π molecular orbitals delocalized along the polymer chains. These materials have attracted much interest for potential applications in optoelectronic devices due to their unique electronic and photonic properties. Recently, interesting studies have been devoted to the synthesis, characterization, physical and chemical properties and variety of these materials. In this work, a quantum-chemical investigation on the structural and opto-electronic properties of new polymer named poly (4-methylythioazole-2.5- diyl)s is carried out. We present a detailed DFT study of geometrical structures and electronic properties of this organic material. Calculated results are compared with experimental data and based on such comparison we try first, to propose an oligomer model and then, to obtain a qualitative understanding the properties of polymer. We discuss the influence of chain length on structural and optoelectronic properties. The numerical predictions are compared to our experimental results. The ground state optimized structures and energies are obtained using the molecular orbital theory and the DFT (B3LYP/6-31G (d)) calculations.