Sulfur Adsorption and Reaction with a TiO2(110) Surface: O↔S Exchange and Sulfide Formation

2001 ◽  
Vol 66 (8) ◽  
pp. 1149-1163 ◽  
Author(s):  
Jan Hrbek ◽  
Jose A. Rodriguez ◽  
Joseph Dvorak ◽  
Tomas Jirsak
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Surface Reaction ◽  
Energy Shift ◽  
Complete Loss ◽  
Oxide Surface ◽  
Large Binding Energy ◽  
Photoemission Data ◽  
Binding Energy Shift ◽  
Sulfur Adsorption

Upon sulfur adsorption on TiO2(110) at 600 K, all surface oxygen is replaced by sulfur. High-resolution photoemission data show a complete loss of oxygen from the surface layer, a large binding energy shift and attenuation of Ti core levels, and the presence of three different S species. The bonding of sulfur is examined using first-principles density-functional calculations and the periodic supercell approach. At saturation the top layer of the oxide surface is converted to sulfide, with the majority of sulfur buckled above the Ti lattice plane and the remaining sulfur bonded in bridging sites. A mechanism for this self-limiting thermodynamically unlikely surface reaction is proposed.

Surface modification of polyamides by direct fluorination

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Tihomir Solomun ◽  
Arnd Schimanski ◽  
Heinz Sturm ◽  
Renate Mix ◽  
Eugen Illenberger
Keyword(s):  
Thin Films ◽  
Nmr Spectra ◽  
Energy Shift ◽  
Amide Group ◽  
Lower Field ◽  
Direct Fluorination ◽  
Large Binding Energy ◽  
Volatile Products ◽  
End Groups ◽  
Binding Energy Shift

Abstract Bulk samples and thin films of polyamides (PA6 and PA12) were exposed to fluorine (1 - 10 vol.-% F2 in N2) and analysed with photoelectron (XPS) and infrared spectroscopy. Fluorination affects both, the amide and the hydrocarbon parts of the polymers. However, only the carbon atom next to the carbonyl is readily fluorinated. Chemical modification of the amide group is apparent in a large binding energy shift (+5 eV) of the N1s level and the appearance of a νCO band at 1734 cm-1. It is concluded that the amide C-N bond is cleaved in the fluorination process and that COOH and NF2 end groups are formed. This conclusion is corroborated by the appearance of ester oxygen in the XPS and by the 19F NMR spectra of the volatile products that show fluorine signals chemically shifted about 200 ppm towards lower field as compared with the CHF environment.

scholarly journals UNFOLDING BAND AND ABSORPTION ENERGY SHIFT OF Si-Ge NANO CRYSTALS FROM FIRST-PRINCIPLES CALCULATIONS

2020 ◽  
Vol 31 ◽  
Author(s):  
Van Quang Tran
Keyword(s):  
Band Gap ◽  
Brillouin Zone ◽  
First Principles ◽  
Density Functional ◽  
Energy Shift ◽  
Valence Band Maximum ◽  
Band Structures ◽  
Electronic Band ◽  
Absorption Energy ◽  
Electronic Band Structures

Physical properties of the Si1-xGex alloys (x being the composition of Ge) can be understood and predicted from their electronic band structures. In this paper, electronic band structures of the Si1-xGex alloys are calculated using the first-principles density functional theory. The supper cell approach employed in our calculations leads to the folding of electronic bands into the smaller Brillouin zone of the supercell, especially at the Γ point. This often leads to the misinterpretation that the materials have direct band gap. The problem can be resolved by the band unfolding technique which allows one to recover the primitive cell picture of band structure of Si1-xGex. As a result, unfolded electronic bands correctly show an indirect band gap with the valence band maximum (VBM) at the Γ point and the conduction band minimum (CBM) shifted away from Γ. The CBM is gradually shifted from a point along ΓX path (associated with Si) to the L point (associated with Ge) with the increased Ge composition x and the switching occurs at x in the range of 0.6~0.8 which is in accordance with the calculation using kp method. Moreover, the additional electron pockets appear and develop at Γ and L. This provides more comprehensive understanding for our recent experimental observations on the shift of the absorption energy assigned to E1 direct transitions within L and Γ points in the Brillouin zone of Si1-xGex alloy nanocrystals.

First-Principles Evaluation of the Potential of Borophene as a Monolayer Transparent Conductor

2017 ◽  
Author(s):  
Lyudmyla Adamska ◽  
Sridhar Sadasivam ◽  
Jonathan J. Foley ◽  
Pierre Darancet ◽  
Sahar Sharifzadeh
Keyword(s):  
First Principles ◽  
Density Functional ◽  
State Of The Art ◽  
Transparent Electrode ◽  
Visible Range ◽  
Two Dimensional ◽  
Transparent Conductor ◽  
Many Body ◽  
Functional Theory ◽  
Many Body Perturbation Theory

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron-phonon and electron-electron interactions, we show that the electrical conductivity is limited by electron-phonon interactions. Our results indicate that both structures are suitable as a transparent electrode.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

uMBD: A Materials-Ready Dispersion Correction that Uniformly Treats Metallic, Ionic, Covalent, and van der Waals Bonding

2019 ◽  
Author(s):  
Minho Kim ◽  
won june kim ◽  
Tim Gould ◽  
Eok Kyun Lee ◽  
Sébastien Lebègue ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Electrode Materials ◽  
Full Range ◽  
Van Der Waals ◽  
Dft Method ◽  
Dispersion Correction ◽  
Computational Overhead ◽  
System A ◽  
Battery Design

<p>Materials design increasingly relies on first-principles calculations for screening important candidates and for understanding quantum mechanisms. Density functional theory (DFT) is by far the most popular first-principles approach due to its efficiency and accuracy. However, to accurately predict structures and thermodynamics, DFT must be paired with a van der Waals (vdW) dispersion correction. Therefore, such corrections have been the subject of intense scrutiny in recent years. Despite significant successes in organic molecules, no existing model can adequately cover the full range of common materials, from metals to ionic solids, hampering the applications of DFT for modern problems such as battery design. Here, we introduce a universally optimized vdW-corrected DFT method that demonstrates an unbiased reliability for predicting molecular, layered, ionic, metallic, and hybrid materials without incurring a large computational overhead. We use our method to accurately predict the intercalation potentials of layered electrode materials of a Li-ion battery system – a problem for which the existing state-of-the-art methods fail. Thus, we envisage broad use of our method in the design of chemo-physical processes of new materials.</p>

The Damping Term, from First Principles

2017 ◽  
Author(s):  
Olle Eriksson ◽  
Anders Bergman ◽  
Lars Bergqvist ◽  
Johan Hellsvik
Keyword(s):  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Spin Dynamics ◽  
Damping Term ◽  
Functional Theory ◽  
Basic Principles ◽  
Sham Equation ◽  
Damping Parameter ◽  
Simulation Cell

In the previous chapters we described the basic principles of density functional theory, gave examples of how accurate it is to describe static magnetic properties in general, and derived from this basis the master equation for atomistic spin-dynamics; the SLL (or SLLG) equation. However, one term was not described in these chapters, namely the damping parameter. This parameter is a crucial one in the SLL (or SLLG) equation, since it allows for energy and angular momentum to dissipate from the simulation cell. The damping parameter can be evaluated from density functional theory, and the Kohn-Sham equation, and it is possible to determine its value experimentally. This chapter covers in detail the theoretical aspects of how to calculate theoretically the damping parameter. Chapter 8 is focused, among other things, on the experimental detection of the damping, using ferromagnetic resonance.

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