A Comparative Density Functional Theory and Density Functional Tight Binding Study of Phases of Nitrogen  Including a High Energy Density Material N8

Capel, Nicholas; Bharania, Devang; Manzhos, Sergei

doi:10.3390/computation3040574

Cited by 7 publications

(7 citation statements)

References 53 publications

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“…For geometry optimizations again the BFGS algorithm implemented in the DFTB+ package was utilized. The DFTB approach as well as the pbc-0-3 parameter set [39] are well justified as reported by a number of previous studies [49][50][51]. The agreement between AIMD and DFTB calculations within the framework of the present paper was ensured by a number of test calculations, e.g.…”

Section: Dftb Setupsupporting

confidence: 80%

Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach

Cvitkovich¹,

Waldhoer²,

El-Sayed³

et al. 2022

Preprint

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Silicon together with its native oxide SiO2 was recognized as an outstanding material system for the semiconductor industry in the 1950s. In state-of-the-art device technology, SiO2 is widely used as an insulator in combination with high-k dielectrics such as HfO2, demanding fabrication of ultra-thin interfacial layers. The classical standard model derived by Deal and Grove accurately describes the oxidation of Si in a progressed stage, however, strongly underestimates growth rates for thin oxide layers. Recent studies report a variety of oxidation mechanisms during the growth of oxide films in the range of 10 A with various details still under debate. This paper presents a firstprinciples based approach to theoretically assess the thermal oxidation process of the technologically relevant Si(100) surface during this initial stage. Our investigations range from the chemisorption of single O2 molecules onto the p(2 × 2) reconstructed Si surface to oxidized Si surface layers with a thickness of up to 20 A. The initially observed enhanced growth rate is assigned to barrierless O2 chemisorption events upon which the oxygen molecule dissociate. We present strong evidence for an immediate amorphization of the oxide layer from the onset of oxidation. Following the oxidation of the first Si layers a slower oxygen incorporation mechanism is available by molecular precursor states that spontaneously dissociate after a few ps. This process dominates until the surface is saturated with oxygen and separated from the Si substrate by a 5 A transition region. Despite the extremely thin layer, the oxide shows structural characteristics of bulk a-SiO2. The saturated surface becomes inert to dissociative reactions and enables the diffusion of molecular oxygen to the Si/SiO 2 interface as assumed within the Deal-Grove model. Further oxidation of the Si substrate is then provided by O2 dissociations at the interface due to the same charge transfer process responsible for the chemisorption at the surface.

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Section: Dftb Setupsupporting

confidence: 80%

Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach

Cvitkovich¹,

Waldhoer²,

El-Sayed³

et al. 2022

Preprint

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“…-45]. The agreement can be considered good for vdW systems [24,46]. The cohesive energy of this crystal is -1.39 eV per TCNE molecule.…”

Section: And Na Insertion Into Vdw Crystalsmentioning

confidence: 57%

“…These parameters can be compared with experimental results that range: a = 7.48-7.51 Å, b = 6.20-6.21 Å and c = 6.99-7.00 Å;  = 90.00°,  = 97.10-97.35° and  = 90.00°[30,[42][43][44][45]. The agreement can be considered good for vdW systems[24,46]. The cohesive energy of this crystal is -1.39 eV per TCNE molecule.…”

mentioning

confidence: 92%

A comparative computational study of lithium and sodium insertion into van der Waals and covalent tetracyanoethylene (TCNE)-based crystals as promising materials for organic lithium and sodium ion batteries

Chen

Manzhos

2016

Phys. Chem. Chem. Phys.

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We present a comparative ab initio study of Li and Na insertion into molecular (van der Waals) crystals of TCNE (tetracyanoethylene) as well as in covalent Li/Na-TCNE crystals. We confirm the structure of the previously synthesized (covalent) Li-TCNE crystal and predict the existence of its Na-TCNE analogue. In the molecular crystals, we compute the maximum voltages to be 3.5 V for Li and 3.3 V for Na, with theoretical capacities of 1247 mA h g(-1) for Li and 416 mA h g(-1) for Na. In the covalent crystals, the maximum voltages are 2.2 V for Li and 2.7 V for Na, and theoretical capacities are 394 mA h g(-1) for Li and 176 mA h g(-1) for Na. Significantly, up to a capacity of 416 mA h g(-1) for both Li and Na in the molecular crystal and 197 mA h g(-1) for Li and 176 mA h g(-1) for Na in the covalent crystal, the insertion of Li and Na would not lead to reactions with common electrolytes. We show that volumetric capacities of organic electrodes need not be low compared to their inorganic counterparts, contrary to popular belief: the molecular TCNE crystal has been computed to achieve the values of 1845 mA h cm(-3) for Li and 615 mA h cm(-3) for Na, respectively. Tetracyanoethylene-based molecular and covalent crystals could therefore become efficient organic cathode and anode materials for Li and Na ion batteries.

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“…In relation to the cg-N structure, another nitrogen-based solid of N8 molecular crystal (stable at ambient pressure) has been predicted [23]. Several phases of nitrogen including highly energetic phase, covalently bound cg-N have been studied by density functional theory (DFT) [24].Polymeric cg-N phase has been studied by the molecular dynamics and metadynamic simulations [25]. Also, using the first-principle calculations the thermodynamic and kinetic stabilities in polymorphs and cg-N have been investigated [26].…”

Section: Introductionmentioning

confidence: 99%

Calculation of the Thermodynamic Quantities for Cubic Gauche Nitrogen (cg-N)

Yurtseven

Akay

2022

International Journal of Thermodynamics

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This work aims to investigate the thermodynamic properties of the cubic gauge nitrogen (cg-N) by calculating the relevant thermodynamic quantities as a functions of temperature and pressure. The thermodynamic quantities of volume (V), thermal expansion (αp), isothermal compressibility (κT), bulk modulus(B), and the heat capacity (Cp) are calculated as a function of temperature at constants pressures (0, 35, 125, 250 GPa) for the cg-N structure. Also, the pressure dependences of V, κT, αp, Cp and γ (macroscopic Grüneisen parameter) are predicted at T= 295 K for this structure. This calculation is caried out by the thermodynamic relations using some literature data. From our calculations, we find that the κT, αp and also B exhibit anomalous behavior as the temperature lowers below about 100 K at constant pressures studied. This is an indication that cg-N transforms to a solid phase at low temperatures (below about 100 K). Experimental measurements can examine this prediction when available in the literature for the cg-N phase. Also, our predictions of the κT, αp, Cp and γ at various pressures (T= 295 K) can be examined experimentally for the cg-N phase. This calculation method can be applied to some other structures.

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A Comparative Density Functional Theory and Density Functional Tight Binding Study of Phases of Nitrogen Including a High Energy Density Material N8

Cited by 7 publications

References 53 publications

Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach

Modeling the Initial Stages of Si(100) Thermal Oxidation: An Ab-initio Approach

A comparative computational study of lithium and sodium insertion into van der Waals and covalent tetracyanoethylene (TCNE)-based crystals as promising materials for organic lithium and sodium ion batteries

Calculation of the Thermodynamic Quantities for Cubic Gauche Nitrogen (cg-N)

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