Phase Properties of Different HfO2 Polymorphs: A DFT-Based Study

Background: Hafnium Dioxide (HfO2) represents a hopeful material for gate dielectric thin films in the field of semiconductor integrated circuits. For HfO2, several crystal structures are possible, with different properties which can be difficult to describe in detail from an experimental point of view. In this study, a detailed computational approach has been shown to present a complete analysis of four HfO2 polymorphs, outlining the intrinsic properties of each phase on the basis of atomistic displacements. Methods: Density functional theory (DFT) based methods have been used to accurately describe the chemical physical properties of the polymorphs. Corrective Hubbard (U) semi-empirical terms have been added to exchange correlation energy in order to better reproduce the excited-state properties of HfO2 polymorphs. Results: the monoclinic phase resulted in the lowest cohesive energy, while the orthorhombic showed peculiar properties due to its intrinsic ferroelectric behavior. DFT + U methods showed the different responses of the four polymorphs to an applied field, and the orthorhombic phase was the least likely to undergo point defects as oxygen vacancies. Conclusions: The obtained results give a deeper insight into the differences in excited states phenomena in relation to each specific HfO2 polymorph.

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The morphology of an intercalated Au layer with its effect on the Dirac point of graphene

Scientific Reports ◽

10.1038/s41598-020-57982-z ◽

2020 ◽

Vol 10 (1) ◽

Cited By ~ 4

Author(s):

Amirhossein Bayani ◽

Karin Larsson

Keyword(s):

Density Functional ◽

Room Temperature ◽

Dirac Point ◽

Wide Bandgap ◽

Point Of View ◽

Experimental Point ◽

Functional Theory ◽

Band Structure Calculations ◽

Graphene Interface ◽

Structure Calculations

AbstractThis is a theoretical investigation where Density Functional Theory (DFT) has been used in studying the phenomenon of Au intercalation within the 4H-SiC/graphene interface. The electronic structure of some carefully chosen morphologies of the Au layer has then been of special interest to study. One of these specific Au morphologies is of a more hypothetical nature, whilst the others are, from an experimental point of view, realistic ones. The latter ones were also found to be energetically stable. Band structure calculations showed that intercalated Au layers with morphologies different from a planar Au layer will induce a band gap at the Dirac point of graphene (with up to 174 meV for the morphologies studied in the present work). It should here be mentioned that this bandgap size is four times larger than the energy of thermal motion at room temperature (26 meV). These findings reveal that a wide bandgap at the Dirac point of graphene comes from an inhomogeneous staggered potential on the Au layer, which non-uniformly breaks the sublattice symmetry. The presence of spin-orbit (SO) interactions have also been included in the present study, with the purpose to find out if SO will create a bandgap and/or band splitting of graphene.

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High-Tc superconductors from the experimental point of view

Uspekhi Fizicheskih Nauk ◽

10.3367/ufnr.0156.198809d.0117 ◽

1988 ◽

Vol 156 (9) ◽

pp. 117-135 ◽

Cited By ~ 65

Author(s):

L.P. Gor'kov ◽

N.B. Kopnin

Keyword(s):

Point Of View ◽

Experimental Point

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Dosimetry and optimization in digital radiography based on the contrast-detail resolution

Brazilian Journal of Radiation Sciences ◽

10.15392/bjrs.v6i3.467 ◽

2018 ◽

Vol 6 (3) ◽

Author(s):

Wilson Otto Gomes Batista ◽

Alexandre Gomes De Carvalho

Keyword(s):

Image Quality ◽

Inverse Image ◽

Point Of View ◽

Complete Analysis ◽

Portable Devices ◽

Evaluation Tool ◽

Air Kerma ◽

Direct Radiography ◽

Definition Of ◽

Entrance Surface Air Kerma

Contrast-detail (C-D) curves are useful in evaluating the radiographic image quality in a global way. The objective of the present study was to obtain the C-D curves and the inverse image quality figure. Both of these parameters were used as an evaluation tool for abdominal and chest imaging protocols. The C-D curves were obtained with the phantom CDRAD 2.0 in computerized radiography and the direct radiography systems (including portable devices). The protocols were 90 and 102 kV in the range of 2 to 20 mAs for the chest and 80 kV in the range of 10 to 80 mAs for the abdomen. The incident air kerma values were evaluated with a solid state sensor. The analysis of these C-D curves help to identify which technique would allow a lower value of the entrance surface air kerma, Ke, while maintaining the image quality from the point of view of C-D detectability. The results showed that the inverse image quality figure, IQFinv, varied little throughout the range of mAs, while the value of Ke varied linearly directly with the mAs values. Also, the complete analysis of the curves indicated that there was an increase in the definition of the details with increasing mAs. It can be concluded that, in the transition phase for the use of the new receptors, it is necessary to evaluate and adjust the practised protocols to ensure, at a minimum, the same levels of the image quality, taking into account the aspects of the radiation protection of the patient.

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Exchange-Correlation Energy Densities and Response Potentials: Connection Between Two Definitions and Analytical Model for the Strong-Coupling Limit of a Stretched Bond

10.26434/chemrxiv.10283678.v1 ◽

2019 ◽

Author(s):

S. Giarrusso ◽

Paola Gori-Giorgi

Keyword(s):

Density Functional Theory ◽

Strong Coupling ◽

Density Functional ◽

Correlation Energy ◽

Order Term ◽

Strong Coupling Limit ◽

Local Form ◽

Coupling Constant ◽

Functional Theory ◽

Exchange Correlation

We analyze in depth two widely used definitions (from the theory of conditional probablity amplitudes and from the adiabatic connection formalism) of the exchange-correlation energy density and of the response potential of Kohn-Sham density functional theory. We introduce a local form of the coupling-constant-dependent Hohenberg-Kohn functional, showing that the difference between the two definitions is due to a corresponding local first-order term in the coupling constant, which disappears globally (when integrated over all space), but not locally. We also design an analytic representation for the response potential in the strong-coupling limit of density functional theory for a model single stretched bond.<br>

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Electronic Structure Benchmark Calculations of Inorganic and Biochemical Carboxylation Reactions

10.26434/chemrxiv.6983264 ◽

2018 ◽

Author(s):

Oscar A. Douglas-Gallardo ◽

David A. Sáez ◽

Stefan Vogt-Geisse ◽

Esteban Vöhringer-Martinez

Keyword(s):

Electronic Structure ◽

Chemical Reactions ◽

Density Functional ◽

Correlation Energy ◽

Electronic Energy ◽

Basis Sets ◽

Electronic Correlation ◽

Correct Description ◽

Carbon Dioxide Co2 ◽

High Level

<div><div><div><p>Carboxylation reactions represent a very special class of chemical reactions that is characterized by the presence of a carbon dioxide (CO2) molecule as reactive species within its global chemical equation. These reactions work as fundamental gear to accomplish the CO2 fixation and thus to build up more complex molecules through different technological and biochemical processes. In this context, a correct description of the CO2 electronic structure turns out to be crucial to study the chemical and electronic properties associated with this kind of reactions. Here, a sys- tematic study of CO2 electronic structure and its contribution to different carboxylation reaction electronic energies has been carried out by means of several high-level ab-initio post-Hartree Fock (post-HF) and Density Functional Theory (DFT) calculations for a set of biochemistry and inorganic systems. We have found that for a correct description of the CO2 electronic correlation energy it is necessary to include post-CCSD(T) contributions (beyond the gold standard). These high-order excitations are required to properly describe the interactions of the four π-electrons as- sociated with the two degenerated π-molecular orbitals of the CO2 molecule. Likewise, our results show that in some reactions it is possible to obtain accurate reaction electronic energy values with computationally less demanding methods when the error in the electronic correlation energy com- pensates between reactants and products. Furthermore, the provided post-HF reference values allowed to validate different DFT exchange-correlation functionals combined with different basis sets for chemical reactions that are relevant in biochemical CO2 fixing enzymes.</p></div></div></div>

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Application of Scattering Parameters to DPL Time-Lag Parameter Estimation at Nanoscale in Modern Integration Circuit Structures

Energies ◽

10.3390/en14154425 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4425

Author(s):

Mariusz Zubert ◽

Zbigniew Kulesza ◽

Mariusz Jankowski ◽

Andrzej Napieralski

Keyword(s):

Integrated Circuits ◽

Time Lag ◽

Estimation Procedure ◽

Micro Electro Mechanical System ◽

Hafnium Dioxide ◽

Parameters Estimation ◽

Phase Lag ◽

Scattering Parameters ◽

Materials Used ◽

Temperature Time

This paper presents the methodology of material parameters’ estimation for the dual-phase-lag (DPL) model at the nanoscale in modern integration circuit (IC) structures. The analyses and measurements performed were used in the unique dedicated micro-electro-mechanical system (MEMS) test structure. The electric and thermal domain of this structure was analysed. Finally, the silicon dioxide (SiO2) temperature time-lag estimation procedure is presented based on the scattering parameters measured by a vector network analyser for the considered MEMS structure together with the 2-omega method. The proposed methodology has the ability to estimate the time-lag parameter with high accuracy and is also suitable for the temperature time-lag estimation for other manufacturing process technologies of ICs and other insulation materials used for integrated circuits such as silicon nitride (Si3N4), titanium nitride (TiN), and hafnium dioxide (HfO2).

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Assessment of Amyloid Forming Tendency of Peptide Sequences from Amyloid Beta and Tau Proteins Using Force-Field, Semi-Empirical, and Density Functional Theory Calculations

International Journal of Molecular Sciences ◽

10.3390/ijms22063244 ◽

2021 ◽

Vol 22 (6) ◽

pp. 3244

Author(s):

Charuvaka Muvva ◽

Natarajan Arul Murugan ◽

Venkatesan Subramanian

Keyword(s):

Force Field ◽

Density Functional ◽

Amyloid Β ◽

Density Functional Theory Calculations ◽

Tau Proteins ◽

Functional Theory ◽

Energy Profiles ◽

Α Helix ◽

Semi Empirical ◽

Β Sheet

A wide variety of neurodegenerative diseases are characterized by the accumulation of protein aggregates in intraneuronal or extraneuronal brain regions. In Alzheimer’s disease (AD), the extracellular aggregates originate from amyloid-β proteins, while the intracellular aggregates are formed from microtubule-binding tau proteins. The amyloid forming peptide sequences in the amyloid-β peptides and tau proteins are responsible for aggregate formation. Experimental studies have until the date reported many of such amyloid forming peptide sequences in different proteins, however, there is still limited molecular level understanding about their tendency to form aggregates. In this study, we employed umbrella sampling simulations and subsequent electronic structure theory calculations in order to estimate the energy profiles for interconversion of the helix to β-sheet like secondary structures of sequences from amyloid-β protein (KLVFFA) and tau protein (QVEVKSEKLD and VQIVYKPVD). The study also included a poly-alanine sequence as a reference system. The calculated force-field based free energy profiles predicted a flat minimum for monomers of sequences from amyloid and tau proteins corresponding to an α-helix like secondary structure. For the parallel and anti-parallel dimer of KLVFFA, double well potentials were obtained with the minima corresponding to α-helix and β-sheet like secondary structures. A similar double well-like potential has been found for dimeric forms for the sequences from tau fibril. Complementary semi-empirical and density functional theory calculations displayed similar trends, validating the force-field based free energy profiles obtained for these systems.

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A quantitative evaluation of computational methods to accelerate the study of alloxazine-derived electroactive compounds for energy storage

Scientific Reports ◽

10.1038/s41598-021-83605-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Qi Zhang ◽

Abhishek Khetan ◽

Süleyman Er

Keyword(s):

Energy Storage ◽

Density Functional ◽

Tight Binding ◽

Computational Cost ◽

Redox Potentials ◽

Storage Compounds ◽

Computational Screening ◽

Chemical Descriptor ◽

Lowest Unoccupied Molecular Orbital ◽

Semi Empirical

AbstractAlloxazines are a promising class of organic electroactive compounds for application in aqueous redox flow batteries (ARFBs), whose redox properties need to be tuned further for higher performance. High-throughput computational screening (HTCS) enables rational and time-efficient study of energy storage compounds. We compared the performance of computational chemistry methods, including the force field based molecular mechanics, semi-empirical quantum mechanics, density functional tight binding, and density functional theory, on the basis of their accuracy and computational cost in predicting the redox potentials of alloxazines. Various energy-based descriptors, including the redox reaction energies and the frontier orbital energies of the reactant and product molecules, were considered. We found that the lowest unoccupied molecular orbital (LUMO) energy of the reactant molecules is the best performing chemical descriptor for alloxazines, which is in contrast to other classes of energy storage compounds, such as quinones that we reported earlier. Notably, we present a flexible in silico approach to accelerate both the singly and the HTCS studies, therewithal considering the level of accuracy versus measured electrochemical data, which is readily applicable for the discovery of alloxazine-derived organic compounds for energy storage in ARFBs.

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Photochemistry of 1-Phenyl-4-Allyl-Tetrazol-5-One: A Theoretical Study Contribution towards Mechanism Elucidation

Applied Sciences ◽

10.3390/app11094045 ◽

2021 ◽

Vol 11 (9) ◽

pp. 4045

Author(s):

Amilcar Duque-Prata ◽

Carlos Serpa ◽

Pedro J. S. B. Caridade

Keyword(s):

Density Functional ◽

Reaction Pathway ◽

Intramolecular Proton Transfer ◽

Polarizable Continuum Model ◽

Uv Spectra ◽

Point Of View ◽

Basis Set ◽

Pathway Evolution ◽

Photodegradation Mechanism ◽

Energetic Point

The photodegradation mechanism of 1-phenyl-4-allyl-tetrazol-5-one has been studied using (time-dependent) density functional theory with the M06-HF, B3LYP, and PBE0 functionals and the VDZ basis set. All calculations have been carried out using the polarizable continuum model to simulate the solvent effects of methanol. The reaction pathway evolution on the triplet state has been characterised to validate a previously postulated experimental-based mechanism. The transition states and minimums have been initially located by local scanning in partial constrained optimisation, followed by a fully relaxed search procedure. The UV spectra has shown to be better described with PBE0 functional when compared with the experimental results, having the M06-HF a shift of 40 nm. From the energetic point of view, the postulated mechanism has been validated in this work showing a concerted photoextrusion of the N2 molecule. The intramolecular proton transfer occurs at a later stage of the mechanism after cyclization of the allyl group on a triplet biradical intermediate. The photoproduct observed experimentally, a pyrimidinone, has been characterised. The infrared spectroscopic reaction profile has also been proposed.

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Photoluminescent Coordination Polymers Based on Group 12 Metals and 1H-Indazole-6-Carboxylic Acid

Inorganics ◽

10.3390/inorganics9030020 ◽

2021 ◽

Vol 9 (3) ◽

pp. 20

Author(s):

Antonio A. García-Valdivia ◽

Estitxu Echenique-Errandonea ◽

Gloria B. Ramírez-Rodríguez ◽

José M. Delgado-López ◽

Belén Fernández ◽

...

Keyword(s):

Carboxylic Acid ◽

Coordination Polymers ◽

Density Functional ◽

Free Ligand ◽

Emission Spectra ◽

Point Of View ◽

Theoretical Point ◽

Fourier Transformed Infrared Spectroscopy ◽

3D Network ◽

The Stability

Two new coordination polymers (CPs) based on Zn(II) and Cd(II) and 1H-indazole-6-carboxylic acid (H2L) of general formulae [Zn(L)(H2O)]n (1) and [Cd2(HL)4]n (2) have been synthesized and fully characterized by elemental analyses, Fourier transformed infrared spectroscopy and single crystal X-ray diffraction. The results indicate that compound 1 possesses double chains in its structure whereas 2 exhibits a 3D network. The intermolecular interactions, including hydrogen bonds, C–H···π and π···π stacking interactions, stabilize both crystal structures. Photoluminescence (PL) properties have shown that compounds 1 and 2 present similar emission spectra compared to the free-ligand. The emission spectra are also studied from the theoretical point of view by means of time-dependent density-functional theory (TD-DFT) calculations to confirm that ligand-centred π-π* electronic transitions govern emission of compound 1 and 2. Finally, the PL properties are also studied in aqueous solution to explore the stability and emission capacity of the compounds.

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