This document summarizes an ab initio study of the electronic band structure and phonon dispersion of silver oxide (AgO) using density functional theory calculations. The LDA+U method predicted AgO to be a semimetal, while the Hartree-Fock calculation predicted a semiconductor with an indirect bandgap of 1.53 eV, consistent with experiments. Phonon calculations showed small splitting between longitudinal and transverse optical modes for higher oxygen vibrations, explaining why Raman spectroscopy could not observe these modes. The study provides insights into the electronic properties and vibrational behavior of the mixed valence silver oxide.
In this work, I am showing a faithful atomistic process of estimating the oxygen migration energetics within BSCF, oxygen migration energy exhibit a strong dependence on different local atomic structures of this doped perovskites. In addition, DFT calculations exhibit the reason of cubic phase stability of this doped perovskite in variable oxygen concentration.
In this work, I am showing a faithful atomistic process of estimating the oxygen migration energetics within BSCF, oxygen migration energy exhibit a strong dependence on different local atomic structures of this doped perovskites. In addition, DFT calculations exhibit the reason of cubic phase stability of this doped perovskite in variable oxygen concentration.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
Computational Study on the Effect of Axial Ligation Upon the Electronic Struc...Roxana Kincses
Computational Study on the Effect of Axial Ligation Upon the
Electronic Structure of Copper (II) Porphyrinate
(CuTPPs = [5,10,15,20-tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate))
- Electronic Structure with Different Axial Ligands
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
Properties of coordination compoundes part 1 of 3Chris Sonntag
Applications of Crystal Field Theory to explain physical properties of coordination compounds, such as color, lattice energy, hydration energy and Spinel types
Solid-state electrolytes exhibit good safety and stability, and are promising to replace current organic liquid electrolytes in rechargeable battery applications. In this talk, we will present our efforts at developing scalable first principles techniques to design novel solid-state electrolytes. Using the recently discovered Li10GeP2S12 lithium super ionic conductor as an example, we will discuss how various properties of interest in a solid-state electrolyte can be predicted using first principles calculations. We will show how the application of these first principles techniques has suggested two chemical modifications, Li10SiP2S12 and Li10SnP2S12, that retains the excellent Li+ conductivity of Li10GeP2S12 at a significantly reduced cost. These modifications have recently been synthesized, and the measured Li+ conductivities are in excellent agreement with our first principles predictions. We will conclude with a demonstration of how relatively expensive first principles calculations can be intelligently scaled and combined with topological analysis to be a useful screening tool for novel solid-state electrolytes.
A detailed study of Transition Metal Complexes of a Schiff base with its Phys...Abhishek Ghara
The many activities of metal ions in biology have stimulated the development of metal based therapeutics. It has been found that biologically active compounds become more effective and bacteriostatic upon chelation with metal ions also the biological activity of many drugs has been shown to be enhanced on complexing with metal ions, hence promoting their use in Pharmacology. The present work deals with the synthesis of metal complexes derived from a novel Schiff base drug synthesized from urea and salicylaldehyde and its physico-chemical analysis to find out ligand- metal ratio of this complex in solution. For the structure elucidation of these complexes “Monovariation method (Mole ratio method/ Yoe-Jones Method)” has been used to ascertain the ligand-metal ratio in the complex. The stability constant of the formed complex was calculated by molar conductance measurement using Modified Job’s method (Method of Continuous Variations). The analysis has been carried out using conductometry. To confirm metal-ligand ratio, conductometric titrations were carried out at room temperature using analytical grade metal salts. Titrations were carried out with “systronics conductivity-meter” using dip type conductivity cell having cell constant 1 at room temperature.
In recent years, there have been great interest in alkali-O2 batteries with extremely high specific energies. Li-O2 batteries offer the greatest theoretical specific energy, but currently suffer from large charging overpotentials and low power densities. Na-O2 offers a somewhat lower theoretical specific energy compared to Li-O2, but still a substantial improvement over today’s lithium-ion batteries. In this talk, we will demonstrate how first principles calculations can provide crucial insight into the workings of alkali-O2 batteries. We will elucidate a facile mechanism for recharging Li2O¬¬2 that is accessible at relatively low overpotentials of ~0.3-0.4V and is likely to be kinetically favored over Li2O2 decomposition. We will also demonstrate that sodium superoxide (NaO2) is predicted to be considerably more stable than sodium peroxide (Na2O2) at the nanoscale. Using first principles calculations, we derive the specific electrochemical conditions to nucleate and retain NaO2 and comment on the importance of considering the nanophase thermodynamics when optimizing an electrochemical system.
Report paper on Graphene Field Effect Transistor, for the Nanoelectronics course, in the Nanotechnology MSc program at the Information and Telecommunication (ICT) school KTH.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
Computational Study on the Effect of Axial Ligation Upon the Electronic Struc...Roxana Kincses
Computational Study on the Effect of Axial Ligation Upon the
Electronic Structure of Copper (II) Porphyrinate
(CuTPPs = [5,10,15,20-tetrakis(N-methylpyridyl-4)porhinato]copper(II)tetratosylate))
- Electronic Structure with Different Axial Ligands
Influence of the alkyl chain length of alkyltriazoles on the corrosion inhibi...Al Baha University
Abstract. Steel is an important material and has been widely used in today's industrial production. Using organic
corrosion inhibitors is an effective means to prevent steel from corrosion. Generally, the molecular structures of
inhibitors can have a major impact on their corrosion inhibition efficiency. In this work, the influence of alkyl chain
length of three alkyltriazoles on the corrosion inhibition of iron has been investigated by density functional based tight
binding (DFTB) approach. Several typical descriptors such as frontier molecular orbital, adsorption energy, density of
states have been discussed in detail. Our findings will contribute to the understanding of the inhibition mechanism and
the designing of novel corrosion inhibitors.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
Properties of coordination compoundes part 1 of 3Chris Sonntag
Applications of Crystal Field Theory to explain physical properties of coordination compounds, such as color, lattice energy, hydration energy and Spinel types
Solid-state electrolytes exhibit good safety and stability, and are promising to replace current organic liquid electrolytes in rechargeable battery applications. In this talk, we will present our efforts at developing scalable first principles techniques to design novel solid-state electrolytes. Using the recently discovered Li10GeP2S12 lithium super ionic conductor as an example, we will discuss how various properties of interest in a solid-state electrolyte can be predicted using first principles calculations. We will show how the application of these first principles techniques has suggested two chemical modifications, Li10SiP2S12 and Li10SnP2S12, that retains the excellent Li+ conductivity of Li10GeP2S12 at a significantly reduced cost. These modifications have recently been synthesized, and the measured Li+ conductivities are in excellent agreement with our first principles predictions. We will conclude with a demonstration of how relatively expensive first principles calculations can be intelligently scaled and combined with topological analysis to be a useful screening tool for novel solid-state electrolytes.
A detailed study of Transition Metal Complexes of a Schiff base with its Phys...Abhishek Ghara
The many activities of metal ions in biology have stimulated the development of metal based therapeutics. It has been found that biologically active compounds become more effective and bacteriostatic upon chelation with metal ions also the biological activity of many drugs has been shown to be enhanced on complexing with metal ions, hence promoting their use in Pharmacology. The present work deals with the synthesis of metal complexes derived from a novel Schiff base drug synthesized from urea and salicylaldehyde and its physico-chemical analysis to find out ligand- metal ratio of this complex in solution. For the structure elucidation of these complexes “Monovariation method (Mole ratio method/ Yoe-Jones Method)” has been used to ascertain the ligand-metal ratio in the complex. The stability constant of the formed complex was calculated by molar conductance measurement using Modified Job’s method (Method of Continuous Variations). The analysis has been carried out using conductometry. To confirm metal-ligand ratio, conductometric titrations were carried out at room temperature using analytical grade metal salts. Titrations were carried out with “systronics conductivity-meter” using dip type conductivity cell having cell constant 1 at room temperature.
In recent years, there have been great interest in alkali-O2 batteries with extremely high specific energies. Li-O2 batteries offer the greatest theoretical specific energy, but currently suffer from large charging overpotentials and low power densities. Na-O2 offers a somewhat lower theoretical specific energy compared to Li-O2, but still a substantial improvement over today’s lithium-ion batteries. In this talk, we will demonstrate how first principles calculations can provide crucial insight into the workings of alkali-O2 batteries. We will elucidate a facile mechanism for recharging Li2O¬¬2 that is accessible at relatively low overpotentials of ~0.3-0.4V and is likely to be kinetically favored over Li2O2 decomposition. We will also demonstrate that sodium superoxide (NaO2) is predicted to be considerably more stable than sodium peroxide (Na2O2) at the nanoscale. Using first principles calculations, we derive the specific electrochemical conditions to nucleate and retain NaO2 and comment on the importance of considering the nanophase thermodynamics when optimizing an electrochemical system.
Report paper on Graphene Field Effect Transistor, for the Nanoelectronics course, in the Nanotechnology MSc program at the Information and Telecommunication (ICT) school KTH.
The International Journal of Engineering & Science is aimed at providing a platform for researchers, engineers, scientists, or educators to publish their original research results, to exchange new ideas, to disseminate information in innovative designs, engineering experiences and technological skills. It is also the Journal's objective to promote engineering and technology education. All papers submitted to the Journal will be blind peer-reviewed. Only original articles will be published.
The papers for publication in The International Journal of Engineering& Science are selected through rigorous peer reviews to ensure originality, timeliness, relevance, and readability.
Theoretical work submitted to the Journal should be original in its motivation or modeling structure. Empirical analysis should be based on a theoretical framework and should be capable of replication. It is expected that all materials required for replication (including computer programs and data sets) should be available upon request to the authors.
A DFT STUDY OF CO GAS ADSORPTION ON METAL DOPED GRAPHENE SHEETvivatechijri
The interaction of Ni-doped graphene sheet with CO molecule is investigated using density
functional theory simulation to analyze the reactivity of doped graphene towards CO molecule. The adsorption
energy is calculated for energetically favorable adsorption of CO on doped graphene sheet. Our result indicates
that the structural properties of NI-doped graphene sheet are influenced by the adsorption of CO. The
electronic band structure result for CO adsorbed on the doped graphene sheet shows the significant changes in
the electronic properties of Ni-doped graphene.
We present the results on electronic and semi-conducting properties of YN in
rocksalt and zinc-blende structure by using FP-LAPW method as implemented in
the Wien2k code. By performing the volume optimization method, a theoretical
lattice constant is obtained which is used for performing our calculations. Results
on density of states (DOS) and energy bands of YN are presented. It is found that
YN acts as a semi-conducting behaviour in both the NaCl and ZB structures.
Structural, Electronic and Gamma Shielding Properties of BxAl1-xAsIJMERJOURNAL
ABSTRACT: The structural and electronic properties of BxAl1-xAs ternary alloys in the zincblende structure were systematically investigated by using the first principles calculations. The local density approximation was used for exchanged and correlation interaction. The calculated band gap bowing parameter was discovered to be mightily composition dependent of the Boron concentration. Additionally, we have calculated some gamma shielding parameters of BxAl1-xAs ternary alloys. Primarily, the values of mass attenuation coefficients (μρ) were calculated using WinXCom computer program and then these parameters were utilized to calculate the values of electron density (Nel) and effective atomic number (Zeff) in the wide energy range (1 keV - 100 GeV).
Simulation Of Algan/Si And Inn/Si Electric - Devicesijrap
In this work, efficient solar-blind metal-semiconductor photodetectors grown on Si (111) by
molecular beam epitaxy are reported. Growth details are described,the comparison enters the
properties electric of InN/Si and AlGaN/Si photodectors with 0.2 µm of AlGaN and InN layers.
Modeling and simulation were performed by using ATLAS-TCAD simulator. Energy band
diagram, doping profile, conduction current density,I-V caracteristic , internal potential and
electric field were performed.
Simulation of AlGaN/Si and InN/Si ELECTRIC –DEVICESijrap
In this work, efficient solar-blind metal-semiconductor photodetectors grown on Si (111) by
molecular beam epitaxy are reported. Growth details are described,the comparison enters the
properties electric of InN/Si and AlGaN/Si photodectors with 0.2 μm of AlGaN and InN layers.
Modeling and simulation were performed by using ATLAS-TCAD simulator. Energy band
diagram, doping profile, conduction current density,I-V caracteristic , internal potential and
electric field were performed.
Simulation of AlGaN/Si and InN/Si ELECTRIC –DEVICESijrap
In this work, efficient solar-blind metal-semiconductor photodetectors grown on Si (111) by
molecular beam epitaxy are reported. Growth details are described,the comparison enters the
properties electric of InN/Si and AlGaN/Si photodectors with 0.2 µm of AlGaN and InN layers.
Modeling and simulation were performed by using ATLAS-TCAD simulator. Energy band
diagram, doping profile, conduction current density,I-V caracteristic , internal potential and
electric field were performed
37 Latest results from GRAAL collaboration - Chinese Physics C (HEP & NP), De...Cristian Randieri PhD
Latest results from GRAAL collaboration - Chinese Physics C (HEP & NP), December 2009, Vol. 33, N. 12, pp. 1249-1253, ISSN: 1674-1137, doi: 10.1088/1674-1137/33/12/032
di V. Vegna, V. Bellini, J. P. Bouquet, L. Casano, A. D'Angelo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, M. Guidal, E. Hourany, A. S. Ignatov, R. Kunnel, A. Lapik, A. Lleres, P. Levi Sandri, F. Mammoliti, G. Mandaglio, M. Manganaro, M. Moricciani, A.N. Mushkarenkov, V. G. Nedorezov, C. Randieri, D. Rebreyend, N. V. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge (2009)
Abstract
The GRAAL experimental set-up consists of a polarized and tagged photon beam that covers an energy range from a minimum of 600 MeV up to a maximum of 1500 MeV, of a liquid Hydrogen or Deuterium target and of the 4π Lagrange detector optimized for photon detection. It allows the study of pseudo-scalar and vector meson photoproduction on the nucleon in the energy range corresponding to the second and the third resonance regions. In the following, the σ beam asymmetries in η and π0 photoproduction on quasi-free nucleon are shown. Also single and double polarization observables in K+Λ photoproduction on free proton are shown; they are important to confirm the role of new or poorly known resonances in the 1900 MeV mass region.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
1. IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE)
e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 5, Issue 5 (May. - Jun. 2013), PP 18-24
www.iosrjournals.org
www.iosrjournals.org 18 | Page
Ab Initio Study of the Electronic and Phonon Band Structure Of
the Mixed Valence Silver Oxide
N. N. Omehe1
, S. Ehika2
1
Federal University, Otuoke, Bayelsa State, Nigeria.
2
Ambrose Alli University, Ekpoma, Edo state, Nigeria.
Abstract: We have performed the electronic band structure and the Phonon dispersion spectra of the mixed
valence Silver oxide in the density functional theory (DFT) framework. We used the LDA+U and the HF
methods in computing the electronic band structure while the LDA was used for the phonon dispersion
calculation. Our structural optimization results agree well with experiment. The LDA+U predicted AgO to be
semimetal nature while the HF calculation predicted a semiconductor nature with a fundamental band gap of
1.53 eV which is in good agreement with experiment. In the phonon calculation, we see that the longitudinal
optical and the transverse optical split is very small for higher modes corresponding to oxygen. This is the
reason while the Raman spectroscopy was not able to observe these modes.
Keywords- Density functional theory, density perturbation functional theory, direct and indirect band gap,
electronic band structure, Hartree Fock and local density approximation.
I. Introduction
Silver oxide (AgO) has attracted so much attention due to its technological applications. It has
applications in battery [1], anti-bacterial activity [2], super-resolution near-field structure (RENS) for optical
read–write ultra-high density non-volatile memories, in fluorescence imaging and the property of surface
enhanced Raman scattering (SERS) in plasmonic devices [3]. It also has applications in optical data storage
devices. Silver oxide is a potential candidate in electric-pulse-induced resistive random access memory
(RRAM), a technique for the next generation of non-volatile memory [2]. It is a semiconductor whose electronic
structure has attracted some controversies, the controversy is about the true state of the mixed oxide. Some
studies claim it is silver(I,II) [4,5,6] while some others claim it is silver(I,III) [7,8].
AgO has been studied experimentally and theoretically to determine its valence mixed state and the
electronic band gap. Bielmann et al [5] in their Ultraviolet photoelectron spectroscopy showed that the
experimental electronic band gap of AgO is dependent on oxidation. Their obtained a band gap of 1.09 eV after
an immediate oxidation step. On further oxidation, they measured a band gap value of 0.52eV. This band
closing is also corroborated in result of the investigation by Raju et al [9]. Park et al [4] in their model of AgO
studied by density functional theory using full-potential linearized augmented plane wave (FLAPW) method
obtained a small indirect band gap of 0.03 eV. Allen et al using the hybrid functional proposed by Heyd et al
[10] obtained an indirect band gap of 1.2 eV and a direct band gap of 1.6 eV. They quarrelled the model by Park
et al, saying it was incapable of modeling the mixed valence silver oxide. The Raman spectroscopy on AgO was
also studied by Raju et al [9].
In this study, we investigate the electronic and vibration properties of AgO. To the best of our
knowledge, this is the first time a theoretical phonon investigation will be carried out. We apply the Hartree-
Fock (HF) and the LDA+U scheme to investigate the electronic band structure of AgO.
II. Computational Detail
AgO crystallizes in a monoclinic structure with a space group P121/c1. The lattice parameters are a
=5.86 Å, b =3.48 Å, c =5.5 Å, and β = 107.5˚ (taking from ref 11). The lattice contains two nonequivalent Ag
sites: Ag(1) has two nearest oxygen atoms with the Ag(1)-O bond length is 2.18 Å; Ag(2) is surrounded by four
oxygen atoms with Ag(2)-O bond lengths of 2.01 and 2.05 Å. Fig. 1 show the structure of AgO adopted for this
investigation.
In this study, we have performed structural relaxation, the electronic band structure and Phonon band
structure of bulk AgO. In the relaxation of AgO, the starting lattice parameters were adopted from the
experimental values of Jansen and Fischer [11]. The two inequivalent Ag occupy the 2b and 2c wyckoff’s
positions. These two were kept fixed while the position of the oxygen was allowed to evolve. The atomic
positions were deemed to have relaxed when the force is 0.01 br/atom. The lattice parameters were then
optimized with the relaxed atomic positions. The results of the structure optimization with previous theoretical
and experimental results are shown in Table 1. The relaxed coordinate for the oxygen atoms and the Ag
coordinates are given in table II. For the electronic band structure, we made use of the Hartree-Fock (HF) and
2. Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
www.iosrjournals.org 19 | Page
local density approximation LDA+U schemes as implemented in the Abinit package [12, 13]. Projector
Augmented Wave (PAW) [14] was use for the LDA+U calculations. In all our calculations, the local density
approximation (LDA) as parametrized by Perdew and Zunger [15] was used. The pseudopotentials used in the
LDA calculations were norm-conserving [16].
Fig 1. Crystal structure of AgO from our relaxation. Gray spheres denote linearly coordinated, Aglin, yellow
spheres denote square planar coordinated Agsq, and red oxygen (generated using CrystalMaker).
In all the calculations, the brillouin zone integration for the self-consistency field run was done with a
k-point mesh of 128. A kinetic cut-off of 20 hartree with a PAW Energy cut-off for the double grid (allows to
transfer data from the normal, coarse, FFT grid to the spherical grid around each atom) of 20 hartree was used in
the LDA+U calculations. The self-consistency calculation was assumed to have converged when the difference
in energy between subsequent iteration was
10
1.0x10
. A plane wave set of 179 was used in the exchange part
of the self energy operator; 89 was used for the wave function in self-energy of the HF calculations. The
wannier90 [17, 18, 19] package was used in the interpolation of the calculated band structure in the HF
calculation. For the phonon calculations, the kinetic energy cut-off of 30 hartree was used for the generation of
the plane waves. The number of wave vectors (q-point) used is 32. Lattice dynamical calculations (phonon
dispersion curves and phonon density of states) are performed within the frame work of the self consistent
density functional perturbation theory (DFPT) [20, 21, 22].
Table 1. The lattice parameters, bond length and the angle for this work , previous DFT calculations and
experiment. The lattice parameters and bond lengths are in Angstrom while angle is in degrees.
This work Ref 8 Ref 8 Ref 8 Exp. ref
11
Exp ref
23
a 5.85 5.97 4.74 5.96 5.86 5.852
b 3.477 3.55 4.62 3.69 3.48 3.475
c 5.499 5.57 5.6 5.53 5.5 5.495
Aglin 2.20 2.15 2.17 2.31 2.16 12.17
Agsq 2.099,2.099 2.01,2.01 2.17 1.99,1.99 2.03,2.02 2.06,2.05
Angle β 107.7˚ 107.33˚ 90.31˚ 102.85˚ 107.56˚ 107.5
3. Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
www.iosrjournals.org 20 | Page
Fig. 2 : The electronic band structure of ago from the LDA+U calculation. The Fermi level is indicated by EF.
Fig. 3 : The electronic band structure of AgO from the HF calculation. The Fermi level is indicated by EF.
Table 2. The atomic coordinates from the relaxation. There are 8 atoms per unit cell Wyckoff’s coordinates
(space group number=14)
Atom x y z
Agsq 0.5 0.5 0.5
Aglin 0.0 0.5 0.0
O 0.264 0.85 0.23
III. Results And Discussions
The electronic band structure of AgO along lines of high symmetry in the first brillioun zone for the
LDA+U and HF calculations are shown in Figs. 2 and 3 respectively. The LDA+U calculation predicted AgO to
be a semi-metal. The true semiconductor nature of AgO was predicted by the HF calculation with a fundamental
indirect band gap of 1.53 eV which is in good agreement with experiment [5, 9] and other theoretical result [8].
The optical direct band gap obtained is 1.85 eV. The valence band maximum (VBM) occurred at the C points
while the bottom of the conduction band is located at the Γ point. There is however qualitative disagreement
with the result of Allen et al. The disagreement is in the location of the valence band maximum (VBM) and the
conduction band minimum (CBM). Their VBM is at the Γ point while their CBM is between the B and D points.
The experimentally observed band gap is 1.1 eV.
The total and partial density of states are presented in Fig. 4. From the total DOS in Fig. 4a, it can be
seen that the states in the energy window between -0.6 and -0.55 is the Ag 5s and O 2s orbital. It is dominated
by the O 2s states.
4. Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
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5. Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
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Fig. 4: The density of states (DOS) from LDA+U method. The Fermi energy is at zero. (a) the total DOS (b)
partial DOS for Aglin (c) partial DOS for Aglin (d) partial DOS for O.
This is clearly seen from the partial DOS of O in Fig. 4d. Valence band and the bottom of the conduction band
are predominantly Ag-d orbitals as seen in the partial density of states of Ag in Figs. 4b and 4c. This Ag-d
dominated valence band is in agreement of the result of Allen et al [8].
Fig. 5: The Phonon dispersion curve for AgO.
The phonon dispersion curves of bulk AgO along several high symmetry lines in the brillouin zone are
displayed in Fig. 5. There are 8 atoms group into 3 types in the unit cell. This gave a total of 24 frequency
modes or bands. Of this number, 3 are acoustic while 21 are optical. The bands are either longitudinal or
transverse. The longitudinal acoustic (LA) mode in the direction Γ-C experiences a softening or downward
bending to meet the first transverse acoustic mode (TA1) at a degenerate point at C. In the Γ-A and Γ-Z
directions, the figure reveal an upward bending of (LA). There is a relatively large splitting of the two TA along
the Γ-C and Γ-A directions when compared to the very small split in the Γ- Z direction. The first three optical
modes at Γ corresponding to the second square planar coordinated silver (Agsq) vibrations are found to be 84.7
cm-1
, 107.7 cm-1
and 119.3 cm-1
representing the longitudinal optical (LO) mode, the second transverse optical
(TO2) mode and first transverse optical (TO1) mode respectively. The six vibration modes or branches
belonging to the two linearly coordinated silver atoms were found to be 138.6 cm-1
, 146.4 cm-1
, 163.7 cm-1
for
TO1, T O2 and LO respectively; and 180.9 cm-1
, 198.2 cm-1
and 265.5 cm-1
for TO1, T O2 and LO respectively
corresponding to the two atoms. The remaining optical branches belong to the four Oxygen atoms. At the C-
point the two TO modes for the first oxygen atom are degenerate with a frequency of 333 cm-1
, 271.4 cm-1
,
277.0 cm-1
and 369.5 cm-1
corresponds to TO1, TO2 and LO respectively. There is a softening of TO1
corresponding to second oxygen atom along the Γ-C direction and becoming degenerate with the LO
corresponding to the first oxygen at the C- point. This downward bending can also be seen in Γ-A and Γ-Z
directions. It can be clearly seen from the Phonon dispersion curve of Figure 5 that the separation between LO
and TO2 branches in the Γ-C, Γ-A and Γ-Z directions is very small. These branches belong to the second oxygen
atom. For the third oxygen atom, there is no TO splitting and the branches are not dispersive in the E-A, A-Γ,
Γ-Z directions. The same is observed for the three highest branches which correspond to the fourth oxygen
6. Ab Initio Study of the Electronic and Phonon Band Structure Of the Mixed Valence Silver Oxide
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atom. The highest mode is at the centre of the BZ and its value is 894.5 cm-1
. The Phonon density of state
(PHDOS) for AgO is shown in Figure 5. The PHDOS is divided into three part which are separated by energy
gaps. The first part which ranges from 0.0 to 0.0018 Ha is dominated by vibrations of Ag character while the
higher energy vibrations originate dominantly from O atoms.
Our study of the vibrational properties of AgO is in disagreement with the Raman spectra of Raju et al
[9]. This is because of the very small LO/TO splitting which cannot be resolved experimentally.
Fig. 6: The Phonon density of state of AgO.
IV. Conclusions
We have performed the electronic band structure and the Phonon dispersion spectra of the mixed
valence Silver oxide in the density functional theory (DFT) framework. We used the LDA+U and the HF
methods in computing the electronic band structure while the LDA was used for the phonon dispersion
calculation. The LDA+U predicted AgO to be semimetal nature while the HF calculation predicted a
semiconductor nature with a fundamental band gap of 1.53 eV which is in good agreement with experiment. In
the phonon calculation, we see that the longitudinal optical and the transverse optical split is very small for
higher modes corresponding to oxygen. This is the reason while the Raman spectroscopy was not able to
observe these modes.
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