scholarly journals ELECTRONIC STRUCTURE OF DIVALENT METAL AZIDES

2017 ◽  
pp. 3-10
Author(s):  
Aleksey Gordienko ◽  
Aleksey Gordienko ◽  
Daniil Filippov ◽  
Daniil Filippov
Keyword(s):  
Experimental Data ◽  
Heavy Metal ◽  
Electronic Structure ◽  
Energetic Materials ◽  
Density Functional ◽  
High Reactivity ◽  
Band Gaps ◽  
Electronic Density ◽  
Heavy Metal Azides ◽  
Band Spectra

Ion-molecular metal azides are well known because of their high reactivity, and nowadays they are widely used as energetic materials. Despite the large amount of experimental data exists on such kind compounds, the number of theoretical studies is still not so large. The aim of the present work is to study of the electronic structure of Me(N3)2 compounds, where Me=Sr, Ca, Cd, Hg. All the calculations have been carried out within the framework of the density functional theory with the use of the numerical pseudo-atomic orbitals basis. The results of the band structure calculations are presented in the work together with a maps of total and partial electronic density; the data on Cd(N3)2 and α-Hg(N3)2 are presented for the rst time. The values of band gaps calculated are in good agreement with those obtained by other authors or estimated in the experiments. The all the crystals under consideration, except of α-Hg(N3)2, are predominantly ionic compounds with a relatively small fraction of the covalent bonding. The overall structure of the valence band spectra, as well as the character of conduction band bottom, is similar to other heavy metal azides. The comparative analysis of the data on band gaps led to the conclusion about lesser stability of the heavy metal azides than that of the second group metal azides, what is also conrmed by the experimental data

scholarly journals Unveiling the Atomic and Electronic Structure of Stacked-Cup Carbon Nanofibers

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
D. W. Boukhvalov ◽  
I. S. Zhidkov ◽  
A. Kiryakov ◽  
J. L. Menéndez ◽  
L. Fernández-García ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Carbon Nanofibers ◽  
Density Functional ◽  
Graphene Quantum Dots ◽  
Quantitative Agreement ◽  
Optical Measurements ◽  
Radiative Relaxation ◽  
Covalent Bonds ◽  
Band Spectra ◽  
Valence Bands

AbstractWe report results of comprehensive experimental exploration (X-ray photoemission, Raman and optical spectroscopy) of carbon nanofibers (CNFs) in combination with first-principles modeling. Core-level spectra demonstrate prevalence of sp2 hybridization of carbon atoms in CNF with a trace amount of carbon–oxygen bonds. The density functional theory (DFT)-based calculations demonstrated no visible difference between mono- and bilayers because σ-orbitals are related to in-plane covalent bonds. The influence of the distortions on π-peak is found to be significant only for bilayers as a result of π–π interlayer bonds formation. These results are supported by both experimental Raman and XPS valence band spectra. The combination of optical measurements with a theoretical modeling indicates the formation of optically active graphene quantum dots (GQDs) in the CNF matrix, with a radiative relaxation of the excited π* state. The calculated electronic structure of these GQDs is in quantitative agreement with the measured optical transitions and provides an explanation of the absence of visible contribution from these GQDs to the measured valence bands spectra.

Electronic structure of heavy-metal azides

2004 ◽  
Vol 47 (10) ◽  
pp. 1056-1061 ◽  
Author(s):  
A. B. Gordienko ◽  
A. S. Poplavnoi
Keyword(s):  
Heavy Metal ◽  
Electronic Structure ◽  
Heavy Metal Azides

Electronic structure of S-nitrosothiols from sulfur K-edge X-ray absorption spectroscopy

2011 ◽  
Vol 89 (2) ◽  
pp. 93-97 ◽  
Author(s):  
Vlad Martin-Diaconescu ◽  
Inna Perepichka ◽  
D. Scott Bohle ◽  
Pierre Kennepohl
Keyword(s):  
Experimental Data ◽  
Electronic Structure ◽  
Absorption Spectroscopy ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Computational Models ◽  
Nitroso Group ◽  
X Ray ◽  
X Ray Absorption

Sulfur K-edge X-ray absorption spectroscopy (S K-edge XAS) was applied to investigate the electronic structure of primary and tertiary S-nitrosothiols. Our experimental data, supported by density functional calculations, indicate that changes at Cα affect the S-nitroso group through both inductive and direct orbital effects. Furthermore, our data are consistent with a weakening of the S–N bond in tertiary S-nitrosothiols as compared to their primary S-nitroso analogues. These results support existing computational models and suggest that the reactivity of S-nitrosothiols is not dominated by the electronics of the S–N bond.

scholarly journals Electronic Structure and High Magnetic Properties of (Cr, Co)-codoped 4H–SiC Studied by First-Principle Calculations

Crystals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 634
Author(s):  
Mengyu Zhang ◽  
Jingtao Huang ◽  
Xiao Liu ◽  
Long Lin ◽  
Hualong Tao
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Density Functional ◽  
Magnetic Moments ◽  
Electronic Transitions ◽  
Electronic Density ◽  
Functional Theory ◽  
Metallic Material ◽  
Near Future ◽  
Co Doped

The electronic structure and magnetic properties of 3d transition metal (Cr, Co)-codoped 4H–SiC were studied by density functional theory within GGA methods. The results show that all doped magnetic atoms have high magnetic properties in both Cr-doped and Co-doped 4H–SiC, resulting in the net magnetic moments of 3.03, 3.02 μ B for Si 35 CrC 36 and Si 35 CoC 36 . The electronic density of states reaches the peak at Fermi level, which is beneficial to the electronic transitions, indicating that Cr-doped 4H–SiC is a semi-metallic material. In addition, the magnetic properties of (Cr, Co)-codoped 4H–SiC were also calculated. The results show that the (Cr, Co)-codoped 4H–SiC system has more stable ferromagnetic properties with ΔE F M of −244.3 meV, and we estimated T C of about 470.8 K for the (Cr, Co)-codoped 4H–SiC system. The (Cr, Co)-codoped 4H–SiC can be ferromagnetic through some mechanism based on hybridization between local Cr:3d, Co:3d and C:2p states. These interesting discoveries will help promote the use of excellent SiC-based nanomaterials in spintronics and multi-function nanodevices in the near future.

Electronic structure and spectroscopy of homoleptic compounds of dimolybdenum using TDDFT

2016 ◽  
Vol 94 (1) ◽  
pp. 20-27
Author(s):  
Pere Vilarrubias
Keyword(s):  
Experimental Data ◽  
Density Functional Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Molecular Orbitals ◽  
Time Dependent ◽  
Electronic Transitions ◽  
Functional Theory ◽  
Dependent Density ◽  
Good Agreement

Ten compounds of dimolybdenum are studied using density functional theory and time-dependent density functional theory. The energy of the strongest symmetry-allowed bands is calculated. The results are then compared with experimental data, when available. The PW91 functional gives results for geometry and for the energy of the δ→δ* band that show good agreement with experimental data. However, the B3LYP functional gives more realistic values for the whole spectrum when the results are compared with experimental data. Finally, the different values of energy of these bands are explained analyzing the molecular orbitals involved in these transitions. Some ligands can act as an unsaturated system in conjugation with the delta bond, modifying the energies of the electronic transitions.

scholarly journals Thermodynamics of Plutonium Monocarbide from Anharmonic and Relativistic Theory

2020 ◽  
Vol 10 (18) ◽  
pp. 6524
Author(s):  
Per Söderlind ◽  
Alexander Landa ◽  
Aurélien Perron ◽  
Emily E. Moore ◽  
Christine Wu
Keyword(s):  
Experimental Data ◽  
Electronic Structure ◽  
Lattice Dynamics ◽  
Density Functional ◽  
Formation Enthalpy ◽  
Spin Orbit ◽  
Functional Theory ◽  
Gibbs Energies ◽  
Anharmonic Lattice ◽  
5F Electrons

Thermodynamics of plutonium monocarbide is studied from first-principles theory that includes relativistic electronic structure and anharmonic lattice vibrations. Density-functional theory (DFT) is expanded to include orbital-orbital coupling in addition to the relativistic spin-orbit interaction for the electronic structure and it is combined with anharmonic, temperature dependent, lattice dynamics derived from the self-consistent ab initio lattice dynamics (SCAILD) method. The obtained thermodynamics are compared to results from simpler quasi-harmonic theory and experimental data. Formation enthalpy, specific heat, and Gibbs energy calculated from the anharmonic model are validated by direct comparison with a calculation of phase diagram (CALPHAD) assessment of PuC and sub-stochiometric PuC0.896. Overall, the theory reproduces CALPHAD results and measured data for PuC rather well, but the comparison is hampered by the sub-stoichiometric nature of plutonium monocarbide. It was found that a bare theoretical approach that ignores spin-orbit and orbital-orbital coupling (orbital polarization) of the plutonium 5f electrons promotes too soft phonons and Gibbs energies that are incompatible with that of the CALPHAD assessment of the experimental data. The investigation of PuC suggests that the electronic structure is accurately described by plutonium 5f electrons as “band like” and delocalized, but correlate through spin polarization, orbital polarization, and spin-orbit coupling, in analogy to previous findings for plutonium metal.

scholarly journals Machine Learning the Quantum-Chemical Properties of Metal–Organic Frameworks for Accelerated Materials Discovery with a New Electronic Structure Database

2020 ◽  
Author(s):  
Andrew Rosen ◽  
Shaelyn Iyer ◽  
Debmalya Ray ◽  
Zhenpeng Yao ◽  
Alan Aspuru-Guzik ◽  
...  
Keyword(s):  
Machine Learning ◽  
Electronic Structure ◽  
Quantum Chemical ◽  
Density Functional ◽  
Metal Organic Frameworks ◽  
Band Gaps ◽  
Structure Property ◽  
Specific Chemical ◽  
Metal Organic ◽  
Structure Properties

<p>Metal–organic frameworks (MOFs) are a widely investigated class of crystalline solids with tunable structures that make it possible to impart specific chemical functionality tailored for a given application. However, the enormous number of possible MOFs that can be synthesized makes it difficult to determine which materials would be the most promising candidates, especially for applications governed by electronic structure properties that are often computationally demanding to simulate and time-consuming to probe experimentally. Here, we have developed the first publicly available quantum-chemical database for MOFs (the “QMOF database”), which consists of properties derived from density functional theory (DFT) for over 14,000 experimentally synthesized MOFs. Throughout this study, we demonstrate how this new database can be used to identify MOFs with targeted electronic structure properties. As a proof-of-concept, we use the QMOF database to evaluate the performance of several machine learning models for the prediction of DFT-computed band gaps and find that crystal graph convolutional neural networks are capable of achieving superior predictive performance, making it possible to circumvent computationally expensive quantum-chemical calculations. We also show how unsupervised learning methods can aid the discovery of otherwise subtle structure–property relationships using the computational findings in this work. We conclude by highlighting several MOFs with low band gaps, a challenging task given the electronically insulating nature of most MOF structures. The data and predictive models generated in this work, as well as the database of MOF structures, should be highly useful to other researchers interested in the predictive design and discovery of MOFs for the many applications dictated by quantum-chemical phenomena.<br></p>

scholarly journals Machine Learning the Quantum-Chemical Properties of Metal–Organic Frameworks for Accelerated Materials Discovery with a New Electronic Structure Database

2020 ◽  
Author(s):  
Andrew Rosen ◽  
Shaelyn Iyer ◽  
Debmalya Ray ◽  
Zhenpeng Yao ◽  
Alan Aspuru-Guzik ◽  
...  
Keyword(s):  
Machine Learning ◽  
Electronic Structure ◽  
Quantum Chemical ◽  
Density Functional ◽  
Metal Organic Frameworks ◽  
Band Gaps ◽  
Structure Property ◽  
Specific Chemical ◽  
Metal Organic ◽  
Structure Properties

<p>Metal–organic frameworks (MOFs) are a widely investigated class of crystalline solids with tunable structures that make it possible to impart specific chemical functionality tailored for a given application. However, the enormous number of possible MOFs that can be synthesized makes it difficult to determine which materials would be the most promising candidates, especially for applications governed by electronic structure properties that are often computationally demanding to simulate and time-consuming to probe experimentally. Here, we have developed the first publicly available quantum-chemical database for MOFs (the “QMOF database”), which consists of properties derived from density functional theory (DFT) for over 14,000 experimentally synthesized MOFs. Throughout this study, we demonstrate how this new database can be used to identify MOFs with targeted electronic structure properties. As a proof-of-concept, we use the QMOF database to evaluate the performance of several machine learning models for the prediction of DFT-computed band gaps and find that crystal graph convolutional neural networks are capable of achieving superior predictive performance, making it possible to circumvent computationally expensive quantum-chemical calculations. We also show how unsupervised learning methods can aid the discovery of otherwise subtle structure–property relationships using the computational findings in this work. We conclude by highlighting several MOFs with low band gaps, a challenging task given the electronically insulating nature of most MOF structures. The data and predictive models generated in this work, as well as the database of MOF structures, should be highly useful to other researchers interested in the predictive design and discovery of MOFs for the many applications dictated by quantum-chemical phenomena.<br></p>

Investigation of Local Coordination and Electronic Structure of Dielectric Thin Films from Theoretical Energy-Loss Spectra

2007 ◽  
Vol 996 ◽  
Author(s):  
Manish K. Singh ◽  
Javier Rosado ◽  
Rajesh Katamreddy ◽  
Anand Deshpande ◽  
Christos G. Takoudis
Keyword(s):  
Experimental Data ◽  
Thin Films ◽  
Electronic Structure ◽  
Energy Loss ◽  
Density Functional ◽  
Random Phase ◽  
Dielectric Tensor ◽  
Full Potential ◽  
Low Loss ◽  
Edge Structure

AbstractQuantum mechanical simulations were performed to calculate the valence electron energy-loss spectra (VEELS) for hafnium oxide, hafnium silicate, silicon oxide and silicon systems using the full potential Linearized Augmented Plane Wave (LAPW) formalism within the Density Functional Theory (DFT) framework. The needed energy-loss function (ELF) was derived from the calculation of the complex dielectric tensor within the random phase approximation (RPA). The calculated spectra were compared with experimental scanning transmission electron microscopy (STEM)/EELS of atomic layer deposited (ALD) HfO2 on Si(100) to evaluate their use as a “fingerprint” method that can be used to distinguish among various polymorphs of HfO2 thin films and relate the fine structure to the electronic structure and local bonding environment. Calculated low-loss spectra are found to be in satisfactory agreement with experimental data. Also, the combination of such theoretical calculations and experimental data could be of key importance in our understanding of fundamental issues of these systems. Compared to energy-loss near edge structure (ELNES) or core energy-loss spectra, the ELF calculated for low-loss spectra is computationally less expensive and can prove useful for prompt analysis.

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