Principles Density Functional Theory Study Research Articles

Insights into the dopant engineering in copper-doped SrTiO3 nanocubes

In recent years, semiconductors have captivated the scientific community due to their potential to harness the abundant and sustainable energy from the sun to effectively treat water pollutants. Herein, we present combined theoretical and experimental insights into the enhanced activity of photocatalytic degradation of cationic and anionic dye viz methylene blue (100% in 90 min) and rose bengal (99.6% in 30 min) in presence of copper doped SrTiO3 catalyst. First principles density functional theory study reveals the introduction of additional states due to copper doping resulting in the decrease in the band gap making it visible light active. Experimental analysis reveals a change in the morphology from broccoli type assorted spherical particles to cubic shaped structures resulting in three times increase in the surface area as a consequence of doping copper. The adopted one pot solvothermal approach not only resulted in materials with high cyclic stability but also resulted in a versatile material, which can be applied for degradation of other dyes.

The effect of Pt and IrO2 interlayers on enhancing the adhesion of Ti/SnO2 interface: A first principles density functional theory study

With potential applications from gas sensors to anode electrodes, Ti/SnO2 interfacial systems play a crucial role in the detection of harmful gases and the destruction of refractory organic pollutants via electrochemical advanced oxidation processes. However, there is an issue with the stability of the Ti/SnO2 interface, in which having an interlayer of another metal or ceramic may work to improve it. First principles density functional theory calculations were performed to study how the addition of Pt and/or IrO2 interlayers affect the stability and adhesion of Ti/SnO2. The calculations showed that Ti/SnO2 interfaces are destabilized by the movement of oxygens from the surface of SnO2 into the Ti phase, causing the adhesion between the newly oxidized Ti phase to be weak with the surface Sn atoms. In contrast, both Pt and IrO2 were found to form stable interfaces with both Ti and SnO2. Further investigation found that Ti/Pt/SnO2 and Ti/IrO2/SnO2 formed stable systems that promoted adhesion between all phases. However, having both Pt and IrO2 combined as interlayers did not form a stable system. Overall, the results show that both Pt and IrO2 may serve as potential interlayer for Ti/SnO2 that promotes adhesion, but combined together they do not.

Charge polarization induced site preferences phenomena of ethylene hydrogenation via electronic metal support interactions

The catalytic activity of supported catalyst is closely related to the electronic metal-support interactions (EMSI). In this paper, first principles density functional theory study was conducted to understand the EMSI between Pd clusters (Pd4, Pd7, Pd10) and CeO2 substrate. When Pd was loaded on CeO2 surface, the electrons of Pd would transfer to the CeO2 substrate via Pd-O bonding interactions. Moreover, the charge redistribution on the Pd cluster leads to significant polarization of electron density. Consequently, the Pd atoms located at the metal-support interface (IF site) are positively charged, while the Pd atoms at the topmost (T site) are negatively charged. The H2 dissociation and ethylene hydrogenation at these sites were calculated with both low and high hydrogen coverage. It was found that the two types of sites should collaborate synergically to promote the hydrogenation of ethylene. In particular, the IF sites exhibit relatively high activity for H2 dissociation, while the T sites show superior catalytic efficiency for ethylene hydrogenation. Therefore, the EMSI induced charge polarization can tune the electronic structure and charge state of supported metal catalysts, which further determines the performance of different region on the catalyst.

Improvement of Ti/TiN interfacial shear strength by doping – A first principles density functional theory study

The dependence of interfacial shear resistance on the substitutional doping of Al, V and Cr at the Ti/TiN interface was studied using first principles Density Functional Theory. Only Al dopants had negative enthalpies of mixing in Ti and at the Ti/TiN interface. Generalized stacking fault energies (GSFE) were calculated and their barriers were used as an estimate of shear resistance. The addition of Al increased the GSFE barriers of pure Ti when they were in adjacent atomic layers. It was found that when Al atoms were in contact, they had a destabilizing effect that led to the increased barriers in certain configurations. Near the Ti/TiN interface, the presence of one or two Al dopants increased the GSFE barrier by drawing some of the electron charge from the ceramic N atoms into the Ti phase. There was a general correlation between higher GSFE barriers and Al concentration at the Ti/TiN interface, which were attributed to both of the described effects: destabilizing Al-Al interactions and Al drawing electron density from the ceramic into the Ti phase.

The hydration of periclase: Atomistic insights from quantum-chemical look

A first principles density functional theory study has been carried out to investigate the hydration kinetics of periclase (MgO) through the interaction between water and periclase (0 0 1) and (1 1 1) surfaces. A single water molecule associatively adsorbs on both surfaces. Dissociative adsorption of water molecule only occurs by the co-adsorption of water on the (0 0 1) surface. Excepting this co-adsorption on the MgO(0 0 1) surface, the adsorption of two or monolayer water molecules on both surfaces are associative in nature. The interaction of water monolayer with the MgO(1 1 1) surface leads to the formation of Mg(OH)2. The calculated energy barrier for the formation of Mg(OH)2 from MgO is 93.6 kJ/mol, which is higher than the experimental values (66–84 kJ/mol). The absence of defect in the model surface sets the upper limit to the energy barrier for the hydration reaction. The effect of surface defects is demonstrated through the adsorption of a single water molecule. A single water molecule adsorbs both associatively and dissociatively on the (1 1 1) defect surface. The energy barrier for the conversion of associative to dissociative adsorption is 36.7 kJ/mol. The important new insights from this study are: (1) only MgO(1 1 1) surface is involved in the hydration of periclase and (2) surface defects play very significant role in the experimental measurement of energy barrier for hydration reaction.

Hyperfine interaction of H-divacancy in diamond

We present a first principles density functional theory study of microscopic properties of hydrogen defect centres in diamond. Several configurations, involving interstitial hydrogen impurities, have been considered either forming with other defects, such as hydrogen defects and vacancies. The atomic structures, and hyperfine parameters of hydrogen result compared with the experimental data on electrically active centres in synthetic diamond. Based on Local density functional theory our calculations are in excellent agreement with one interpretation of electron paramagnetic resonance of hydrogen in diamond.

First principles density functional theory study of Pb doped α-MnO2 catalytic materials

The impact of Pb in the tunnels of manganese oxide octahedral molecular sieves on chemical state of Mn species and lattice oxygen were investigated utilizing density functional theory calculations. The results show that the Pb dopant in the tunnels of OMS-2 could reduce the average valence states of Mn. The lower energy required for bulk oxygen defects formation in Pb-OMS-2 validates the activation of lattice oxygen by inclusion of tunnel dopant. The inclusion of Pb promotes the catalytic oxidation activity of OMS-2 by reducing the energy required for the surface lattice oxygen migration during the Mars – van Krevelen oxidation process.

Exploring d0 magnetism in doped SnO2–a first principles DFT study

In search of d0 magnetism, the magnetic behavior of SnO2 with cation substitution from group1A (Li, Na, K) and group 2A (Be, Mg, Ca) elements has been systematically studied using Density Functional Theory (DFT). While an impurity from group 1A elements switches on ferromagnetism at a lower concentration itself, sufficient hole density is required for a group 2A impurity to create a spontaneous spin polarized ground state, a finding that has not been reported in earlier investigations. Our DFT results predict for the first time that impurities from group 2A (Mg, Ca) in SnO2 can promote room temperature ferromagnetism. Further, the emergence of ferromagnetism due to doping from group 1A elements, which injects three holes per defect, has been mapped successfully onto a modified Hubbard model from the literature. Doping of a single Na atom in the supercell (concentration 6.25 at%) makes the system ferromagnetic, with a magnetic moment close to 3.0μB per defect, and a Curie temperature of 815K, obtained in the mean field approximation. This agrees closely with a model prediction of 750K. Finally, the triggering of ferromagnetism by an impurity atom from group 2A, which adds two holes per defect in the system, implies that the prescription of three holes per defect given in the literature is not a necessary criterion for hole induced ferromagnetism. Rather, the analysis of the density of states and ferromagnetic coupling indicate that the system needs a critical hole concentration to activate ferromagnetism, by pushing the Fermi level inside the valence band in order to satisfy the Stoner criterion.

Adsorption of nucleobases on 2D transition-metal dichalcogenides and graphene sheet: a first principles density functional theory study

Adsorption of nucleobases A, T, G, C and U on transition-metal dichalcogenides such as MoS2 and WS2 is studied using PBE, DFT-D2 and vdW-DF methods.

The location of atomic hydrogen in NiTi alloy: A first principles study

A first principles density functional theory study to investigate the H defect in NiTi alloy is presented. We have determined the interstitial H atom position in bulk B2 phase NiTi alloy. H positions on both the Ti and Ni terminated NiTi surfaces are calculated. Surface adsorptions of H atom on Ni/Ti terminated surfaces are calculated for a low surface coverage of 1.96×1014cm−2. We have also calculated the penetration barrier energy for an H atom from the surface site to the bulk lattice site.

The relationship between formate adsorption energy and electronic properties: A first principles density functional theory study

First principles density functional theory calculations have been performed for the chemisorption of formate adsorption on some metal surfaces. For the most stable adsorption site of short- bridge, the calculated formate adsorption energy follows the order of Au(110) < Ag(110) < Cu(110) < Pd(110) < Pt(110) < Ni(110) < Rh(110) < Fe(100) < Mo(100), and a clear linear correlation exists between the adsorption energy and the corresponding heat of formation of metal oxides. Moreover, it has been found that the formate adsorption energy for the transition metals can be correlated well with its d-band center (ɛd), and the IB Group metals can be described by the coupling matrix element square (Vad2).

Intermediates in the hydrogenation of benzene to cyclohexene on Pt(1 1 1) and Pd(1 1 1): A comparison from DFT calculations

Catalytic hydrogenation of aromatic compounds is an important process in petroleum industry. Understanding it through experimental or theoretical research can help to improve its efficiency. This work presents a first principles density functional theory study of the intermediates for the first four hydrogenations steps of the smallest aromatic compound, benzene, into C 6H 10 species, on two popular catalytic metals, palladium and platinum, described by periodic models. Different structures have been studied for the intermediate C 6H 6+ n species, with a various degree of conservation of the conjugation. Some intermediates would present in gas phase a closed-shell conjugated structure, while other would correspond to multiple radicals with a massive destruction of the benzene π system. The Pd and Pt(1 1 1) surfaces strongly differ in terms of most stable structure for the intermediates. On Pd the most conjugated intermediates, i.e. the most stable in gas phase, is clearly preferred. In contrast, on Pt, multiple radical species, highly unstable in gas phase, are strongly stabilized by coupling with the surface. This thermodynamic study indicates a different trend for the hydrogenation mechanism: a clear successive 1–2–3… hydrogenation of neighboring carbon atoms on Pd keeping the largest conjugated fragment, and a nonconsecutive attack, with a maximum breaking of benzene conjugation on Pt.

Characterization of methoxy adsorption on some transition metals: A first principles density functional theory study

Based on the gradient-density functional theory, calculation results of methoxy adsorption on Au(111), Ag(111), Cu(111), Pt(111), Pd(111), Ni(111), Rh(111), and Fe(100) surfaces are presented, and a consistent picture for some key physical properties determining the reactivity of metals appears. These eight metals belong to two groups: either with filled d electrons (group IB) or with unfilled but more than half filled d electrons (group VIII). The calculated adsorption energies are quite in agreement with the experimental data as well as the previous theoretical calculation results. Importantly, using the analysis of B. Hammer and J. K. Norskov, Nature (London) 376, 232 (1995) and in Chemisorption and Reactivity on Supported Clusters and Thin Films, edited by R. M. Lambert and G. Pacchioni (Kluwer Academic, Dordrecht, 1997), pp. 285-351, the binding energies have selectively been linearly correlated to the d-band center and to the size of the metal d-band orbital overlapping with the adsorbate (coupling matrix element) for these two groups of metals. And by analyzing the nature of the adsorption bonding, the possible reason of this difference is suggested.