Crystal Orbital Overlap Population Analysis Research Articles

Substitution effect on electronic and optical properties of Tetraphenyldipyranylidene; A theoretical study

Density functional theory was used to study the structural, electronic, and optical properties of Tetraphenyldipyranylidene (DPPh) solid structure and its derivatives including electron-acceptor atoms and electron-donor groups. The nature of chemical bonding was investigated by crystal orbital overlap population analysis. The simulation results show that DPPh having electron-acceptor atoms (F, Cl, and Br) represent more favorable electronic and optical properties than that of electron-donor groups (CH3, C(CH3)3, OCH3, and OCH2CH3). Also, Br and Cl atoms improve both hole and electron transport of DPPh, which can be considered as a new series of promising ambipolar semiconductors. Finally, DPPh-Br and DPPh-Cl semiconductors are suggested as the preferred candidates for use in electronic devices in comparison with others derivatives.

Prediction of Transition-State Scaling Relationships and Universal Transition-State Vibrational and Entropic Correlations for Dehydrogenations

Linear scaling relationships (LSRs) and Brønsted–Evans–Polanyi (BEP) or transition-state scaling (TSS) relations aid with the prediction of electronic energies. However, temperature effects and pre-exponentials are often taken as constants across metal surfaces or a homologous series. Vibrational scaling relationships (VSRs) offer a way to determine such parameters. Transition-state VSRs (TSVSRs) between local minima and transition states of AHX (A = C, N, O) surface diffusions correlate with BEP relations and broaden to thermochemical property scaling. Using density functional theory, we extend TSVSRs to AHX dehydrogenation reactions on transition-metal surfaces, relating vibrational modes of local minima to transition states. We first predict the slopes of the TSS relations by incorporating bond angles using the Slater–Koster structure factors and hybridization through crystal orbital overlap population analysis and energy overlap integrals between adsorbates and metal surfaces. Additionally, we uncover universal thermochemical property scaling, enabling the estimation of entropies and temperature corrections to enthalpies across a homologous series. We demonstrate both significant vibrational corrections in reactions with low intrinsic electronic barriers and considerable variation in the pre-exponential of a simple dehydrogenation reaction across metals and AHX adsorbates.

Ab initio study of ionic nature of 0.75AgI:0.25AgCl

Ab initio calculations based on density functional theory are performed for zinc-blende structured new host 0.75AgI:0.25AgCl. Eight configurations are simulated for different positions of Cl atoms, and they are divided into three sets of configurations. Similar calculations are also performed for zinc blende β-AgI. Bond lengths are changed and p-d hybridization is observed in all configurations. Ionic nature of atomic bonds is analyzed by the ionicity factor. The charge density analysis also exhibits the ionic and least covalent nature of bonds of AgI and AgCl atoms. The structural parameters are calculated to observe the bulk modulus. Crystal orbital overlap population analysis explains the inter-atomic bond strength which explains the bond breaking energy and activation energy of all configurations.

First principle studies on electronic structure and charge density of potato starch

The electronic and chemical bonding properties of biomaterial potato starch within the density functional theory are presented in this paper, with the aim to be used in electrochemical devices and biomedical applications. In the density of states and projected density of states analysis, the energy difference between the highest occupied molecular orbital and lowest unoccupied molecular orbital is reduced by 2.9 eV, which exhibits the semi-conducting behaviour of modified potato starch in the presence of NaI salt. Calculated charge density predicts the bonding properties and crystal orbital overlap population analysis exhibits the increase of amorphous nature and ionic conductivity due to sodium ion concentration. In this theoretical study, different behaviours of modified potato starch are clearly seen in the presence of NaI salt.

First-principles study on phase transition and ferroelectricity in lithium niobate and tantalate

The phase transitions and ferroelectricity of LiNbO3 and LiTaO3 have been investigated theoretically from first principles. The phonon analyses and the molecular dynamics simulations revealed that the ferroelectric phase transition is not conventional displacive type but order-disorder type with strong correlation between cation displacements. According to the evaluated potential energy surfaces around the paraelectric structures, the large difference in ferroelectricity between the two oxides results from the little difference in short-range interionic interaction between Nb-O and Ta-O. As the results of the crystal orbital overlap population analyses, the different short-range interaction originates from the difference in covalency between Nb4d-O2p and Ta5d-O2p orbitals, particularly dxz-px/dyz-py orbitals (π orbitals), from the electronic point of view.

Vacancy-induced toughening in hard single-crystal V0.5Mo0.5Nx/MgO(0 0 1) thin films

Using a combination of experiments and density functional theory (DFT), we demonstrate the first example of vacancy-induced toughening, in this case for epitaxial pseudobinary NaCl-structure substoichiometric V0.5Mo0.5Nx alloys, with N concentrations 0.55⩽x⩽1.03, grown by reactive magnetron sputter deposition. The nanoindentation hardness H(x) increases with increasing vacancy concentration from 17GPa with x=1.03 to 26GPa with x=0.55, while the elastic modulus E(x) remains essentially constant at 370GPa. Scanning electron micrographs of indented regions show ductile plastic flow giving rise to material pile-up, rather than cracks as commonly observed for hard, but brittle, transition-metal nitrides. The increase in alloy hardness with an elastic modulus that remains constant with decreasing x, combined with the observed material pile-up around nanoindents, DFT-calculated decrease in shear to bulk moduli ratios, and increased Cauchy pressures (C12–C44), reveals a trend toward vacancy-induced toughening. Moreover, DFT crystal orbital overlap population analyses are consistent with the above results.

Adsorption of ammonia on vanadium–antimony mixed oxides

We analyzed the adsorption of ammonia (NH3) on the VSbO4(110) catalyst surface using density functional theory (DFT) calculations. We followed the evolution of the chemical bonds between different atoms of the resulting NH3/VSbO4 system and the changes in the electronic structure of the catalyst. NH3 preferential adsorption geometries were analyzed through the crystal orbital overlap population (COOP) concept and the density of states (DOS) curves. The VSbO4(110) surface exhibits Lewis and Brønsted acid sites on which the ammonia molecule can interact. On the Lewis acid site, NH3 adsorption resulted in the interaction between the N and a surface V-isolated cation. On Brønsted acid site, N interacted with a surface H coming from the chemical dissociation of water. The COOP analysis indicate that NH3 interaction on the VSbO4(110) surface is weak. In addition, the DOS curves show more developed electronic interactions for NH3 adsorption on Lewis acid site than over Brønsted acid site.

YbOs4Sb12 Filled Skutterudite: Its Electronic Properties

A theoretical calculation on YbOs4Sb12 filled skutterudite is reported. The calculated energy bands yield indication of a semimetallic behavior, while the projected density of states provide support for the existence of hybridization formed by Yb f-, Os d-, and Sb p-states. From the analysis of the energy bands that crosses the E f, it is possible to infer a high effective mass; this value is added to the existence of a strong hybridization yielded indication of the heavy Fermion behavior for this compound which agrees with the experimental information available. The absence of a minigap provides an indication that this compound is not likely to serve as a good thermoelectric material, unless doped in a certain direction as to enhance the probability to open the necessary minigap between the valence and conduction bands. Crystal orbital overlap population analysis yielded indication for the absence of a ferromagnetic instability.

Theoretical study of the electronic properties ofPrM2B2C(M=Co,Ni,Pt)

Full substitution of Ni by the transition metals Co and Pt in $\mathrm{Pr}{M}_{2}{\mathrm{B}}_{2}\mathrm{C}$ $(M=\mathrm{Ni},\mathrm{Co},\mathrm{Pt})$ is analyzed using tight binding within the extended Huckel method. Electronic structure calculation, total and projected density of states (PDOS), Mulliken population, and crystal orbital overlap population analysis were examined in order to elucidate the absent or presence of superconductivity. Band-structure calculation shows small differences in $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ compounds. The total and PDOS crossing the Fermi energy $({E}_{F})$ is located in a valley and is dominated by $\ensuremath{-}d$ states, which are principally responsible for the metallic character in both compounds. For $\mathrm{Pr}∕\mathrm{Pt}$ compound, the band structure as well as the total and PDOS are fully different, since two sets of bands, the $\ensuremath{-}f$ and $\ensuremath{-}d$ bands, are highly localized at the ${E}_{F}$, contributing both bands to the electronic conduction. Besides, weak hybridization with important contribution of the C $\ensuremath{-}p$ state is observed in $\mathrm{Pr}∕\mathrm{Pt}$ with respect to the $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ compound, where in these last compounds, the C $\ensuremath{-}p$ contribution is null. Furthermore, Mulliken population analysis and average net charge indicated unfilled $\ensuremath{-}d$ orbital with charge transference inside the ${M}_{2}{\mathrm{B}}_{2}$ layer for $\mathrm{Pr}∕\mathrm{Ni}(\mathrm{Co})$. The situation is totally different for $\mathrm{Pr}∕\mathrm{Pt}$ superconductor compounds, since an almost filled $\ensuremath{-}d$ orbital and homogeneous charge distribution were observed. These theoretical evidences suggest that the absence of the superconductivity in $\mathrm{Pr}∕\mathrm{Ni}$ and $\mathrm{Pr}∕\mathrm{Co}$ are connected by the remarkable instabilities between $\ensuremath{-}d$, $\ensuremath{-}p$, and $\ensuremath{-}f$ states, with respect to that observed in the superconductor $\mathrm{Pr}{\mathrm{Pt}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ compounds.

Electronic properties of Co and Ni silicides: a theoretical approach using extended Huckel method

AbstractCalculations of electronic structure, total and projected density of states (DOS), crystal orbital overlap population (COOP), and average net charge, and also Mulliken population analysis, were performed to study electronic properties of Co and Ni silicides. Analysis of the energy bands depicts metallic behavior for both silicides.The projected DOS yields an indication that hybridization occurs for Co and Ni silicides. The hybridized band in CoSi2 is composed of Co d and p orbitals and Si p and s orbitals, while in NiSi2 the hybridized band is formed by Ni d and p orbitals with Si p orbitals. The fact that the Fermi energy crosses a small part of the DOS, as is the case of CoSi2, yields an indication of the different electronic properties of CoSi2 when compared to NiSi2. The hybridization is stronger in CoSi2 than in NiSi2. Mulliken population analysis provides an indication that a smaller charge distribution exists in NiSi2 when compared to CoSi2. This difference in charge distribution accounts for the different electronic behavior, in agreement with the DOS analysis. Moreover, COOP analysis provides an indication of the existence of covalent bonding between M and Si (M = Ni, Co), this being stronger in Co than in Ni silicides. Furthermore, the average net charge in both compounds yields an indication that there is a charge transfer from M towards Si. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal Orbital Overlap Population Analysis of the Capacity Fading of Metal‐Substituted Spinel Lithium Manganate LiMn2 O 4

The capacity fading with charge‐discharge cycles, which is a problem in the practical use of spinel lithium manganate for the positive electrode material of a lithium ion rechargeable battery, is analyzed using extended Hückel band calculations. The strength of the manganese‐oxygen bond is characterized by crystal orbital overlap population (COOP) analyses. The manganese atom in lithium manganate is substituted with first‐row transition metal atoms, and the COOP is calculated and analyzed. The COOP of substituted lithium manganate is compared with the experimental data for the capacity performance in charge‐discharge cycles. Both showed very good agreement. We understand by examining the Mn‐O COOP that the suppression of capacity fading with manganese substitution in lithium manganate by Fe, Co, and Ni has relevance to an increase in the strength of the Mn‒O bond. COOP is a good index for the capacity fading with charge‐discharge cycles for the substituted lithium manganate. It is applicable to the search and examination for the best composition in the lithium manganate material system whose properties are influenced by the Mn‒O bond. © 2000 The Electrochemical Society. All rights reserved.

A new theoretical approach for the electrical properties of TiX2 (X=S, Se, Te) phases with density functional calculations

The electronic structures of layered transition metal dichalcogenides TiX2 (X=S, Se, Te) have been studied with the Amsterdam Density Functional package for periodic systems (ADF-BAND). The accuracy of this algorithm to calculate the charge transfer between the chalcogens and the metal has been tested at different levels of approximation (local-density approximation, generalized gradient corrections of Becke–Perdew and Perdew–Wang, and quasirelativistic calculations). The total and partial density of states of the three compounds, as well as the crystal orbital overlap population analysis, have been used to rationalize the electronic structure of the systems. The present results show a significant p/d-block band overlap for TiTe2, leading to a Te(5p)→Ti(3d) electron transfer and a metallic behavior. Conversely, owing to the redox competition between the metal and the chalcogens, TiS2 and TiSe2 are predicted to be a semiconductor and a semimetal respectively. These physical properties are discussed in terms of electron density displacement from the chalcogen to the titanium when going from TiS2 to TiTe2. The relativistic effects appear to have no significant influence on the global physical properties of these layered compounds, although they slightly reduce the Te(5p)→Ti(3d) electron transfer.