Study of Silicon-metal Interaction in Adsorption Process: An Ab-initio Approach

2011 ◽  
Vol 1305 ◽  
Author(s):  
Sudip Chakraborty ◽  
S. V. Ghaisas ◽  
Chiranjib Majumder
Keyword(s):  
Metal Surface ◽  
Density Functional ◽  
Electrical Contact ◽  
Island Size ◽  
Functional Theory ◽  
The Difference ◽  
Ab Initio Approach ◽  
Bulk Gold ◽  
Cluster Level

Abstract:The formation of metal silicide plays important role in deciding the nature of the contact on silicon.Due to their chemically neautral nature,Au and Ag are used as contact metals in various devices.In particular the role of silicides is known to be crucial in defining the behavior of the electrical contact. The interaction of these metals with silicon at cluster level is still under the study.For naoscale devices, the nature at such interaction carries lot more inportance. Bulk Gold silicide(Cohesive energy ~ 3.81eV/atom) shows higher stability compared to silver silicide(Cohesive enrgy ~ 2.95 eV/atom). In the present work we show computational results based on Density Functional Theory(DFT) of Si cluster adsorption on Ag(111) surface and compare with the results of Si adsorption on Au(111). These results bring out the difference in Si cluster-metal surface interactions at the nanoscale. In particular the Si island-metal surface interaction shows island size dependence. We have presented results for most stable orientations only.

scholarly journals The Role of the Active Site Tyrosine in the Mechanism of Lytic Polysaccharide Monooxygenase

2020 ◽  
Author(s):  
Aina McEvoy ◽  
Joel Creutzberg ◽  
Raushan Kumar Singh ◽  
Morten J. Bjerrum ◽  
Erik Hedegård
Keyword(s):  
Active Site ◽  
Density Functional ◽  
Renewable Resource ◽  
Lytic Polysaccharide Monooxygenase ◽  
Functional Theory ◽  
Polysaccharide Monooxygenases ◽  
Active Site Tyrosine ◽  
The Difference ◽  
First Time

Natural polysaccharides (such as cellulose) comprise a large bio-renewable resource. However, exploitation of this resource requires energy-efficient polysaccharide degradation, which is currently limited by the inherent recalcitrance of many naturally occurring polysaccharides. Catalytic breakdown of polysaccharides can be achieved more efficiently by means of the enzymes lytic polysaccharide monooxygenases (LPMOs). However, the LPMO mechanism has remained controversial, preventing full exploitation of their potential. One of the controversies has centered around an active site tyrosine, present in most LPMOs. Different roles for this tyrosine have been proposed without direct evidence, but two recent investigations have for the first time obtained direct (spectroscopic) evidence for that chemical modification of this tyrosine is possible. Surprisingly, the spectroscopic features obtained in the two investigations are remarkably different. In this paper we use density functional theory (DFT) in a QM/MM formulation to reconcile these (apparently) conflicting results. By modeling the spectroscopy as well as the underlying reaction mechanism we can show how formation of two isomers (both involving deprotonation of tyrosine) explain the difference in the experimental observed spectroscopic features. The link between our structures and the observed spectroscopy provides a firm ground to investigate the role of tyrosine.

scholarly journals Epoxidation of propene using Au/TiO2: on the difference between H2 and CO as a co-reactant

2017 ◽  
Vol 7 (11) ◽  
pp. 2252-2261 ◽  
Author(s):  
Shamayita Kanungo ◽  
Yaqiong Su ◽  
M. F. Neira d'Angelo ◽  
Jaap C. Schouten ◽  
Emiel J. M. Hensen
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Reducing Gas ◽  
Propene Oxide ◽  
The Difference

The role of the reducing gas in the direct epoxidation of propene to propene oxide (PO) using O2 over a Au/TiO2 catalyst was studied through experiments and density functional theory calculations.

scholarly journals The Role of the Active Site Tyrosine in the Mechanism of Lytic Polysaccharide Monooxygenase

2020 ◽  
Author(s):  
Aina McEvoy ◽  
Joel Creutzberg ◽  
Raushan Kumar Singh ◽  
Morten J. Bjerrum ◽  
Erik Hedegård
Keyword(s):  
Active Site ◽  
Density Functional ◽  
Protective Role ◽  
Lytic Polysaccharide Monooxygenase ◽  
Functional Theory ◽  
Polysaccharide Monooxygenases ◽  
Active Site Tyrosine ◽  
The Difference ◽  
First Time

<p>Catalytic breakdown of polysaccharides can be achieved more efficiently by means of the enzymes lytic polysaccharide monooxygenases (LPMOs). However, the LPMO mechanism has remained controversial, preventing full exploitation of their potential. One of the controversies has centered around an active site tyrosine, present in most LPMO classes. Recent investigations have for the first time obtained direct (spectroscopic) evidence for that chemical modification of this tyrosine is possible. However, the spectroscopic features obtained in the different investigations are remarkably different, with absorption maximum at 420 and 490 nm, respectively. In this paper we use density functional theory (DFT) in a QM/MM formulation to reconcile these (apparently) conflicting results. By modeling the spectroscopy as well as the underlying reaction mechanism we can show how formation of two isomers (both involving deprotonation of tyrosine) explain the difference in the observed spectroscopic features. Both isomers have a [TyrO-Cu–OH]<sup>+</sup> moiety with the OH in either <i>cis</i>- or <i>trans</i>-position to a deprotonated tyrosine. Although the <i>cis</i>-[TyrO-Cu–OH]<sup>+</sup> moiety is well positioned for oxidation of the substrate, preliminary calculations with substrate reveal that the reactivity is at best moderate, making a protective role of tyrosine more likely.</p>

The Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge XAS

2020 ◽  
Author(s):  
Tulin Okbinoglu ◽  
Pierre Kennepohl
Keyword(s):  
Density Functional ◽  
Chemical Properties ◽  
Functional Theory ◽  
Rotational Barriers ◽  
Td Dft ◽  
Nitrogen Bonds ◽  
X Ray Absorption ◽  
Related Compounds ◽  
And Chemical Properties

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest due to their many uses and chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet their continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge x-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to explore the role of S<sub>3p</sub> contributions to π-bonding in sulfonamides, sulfinamides and sulfenamides. We explore the nature of electron distribution of the sulfur atom and its nearest neighbors and extend the scope to explore the effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with TD-DFT calculations confirm that sulfonamides, and the other sulfinated amides in this series, have essentially no S-N π bonding involving S<sub>3p</sub> contributions and that electron repulsion and is the dominant force that affect rotational barriers.

γ-Valerolactone-Introduced Controlled-Isomerization of Glucose for Lactic Acid Production over Sn-Beta Catalyst

2021 ◽  
Author(s):  
Xinpeng Zhao ◽  
Zhimin Zhou ◽  
hu luo ◽  
Yanfei Zhang ◽  
Wang Liu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lactic Acid ◽  
Dft Calculations ◽  
Acid Production ◽  
Density Functional ◽  
Lactic Acid Production ◽  
Hydrothermal Conversion ◽  
Functional Theory ◽  
Environment Friendly

Combined experiments and density functional theory (DFT) calculations provided insights into the role of the environment-friendly γ-valerolactone (GVL) as a solvent in the hydrothermal conversion of glucose into lactic acid...

scholarly journals Role of Chemistry and Crystal Structure on the Electronic Defect States in Cs-Based Halide Perovskites

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1032
Author(s):  
Anirban Naskar ◽  
Rabi Khanal ◽  
Samrat Choudhury
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Covalent Bond ◽  
Density Functional Theory Calculations ◽  
Antisite Defect ◽  
Defect States ◽  
Functional Theory ◽  
Electronic Defect ◽  
Constituent Elements

The electronic structure of a series perovskites ABX3 (A = Cs; B = Ca, Sr, and Ba; X = F, Cl, Br, and I) in the presence and absence of antisite defect XB were systematically investigated based on density-functional-theory calculations. Both cubic and orthorhombic perovskites were considered. It was observed that for certain perovskite compositions and crystal structure, presence of antisite point defect leads to the formation of electronic defect state(s) within the band gap. We showed that both the type of electronic defect states and their individual energy level location within the bandgap can be predicted based on easily available intrinsic properties of the constituent elements, such as the bond-dissociation energy of the B–X and X–X bond, the X–X covalent bond length, and the atomic size of halide (X) as well as structural characteristic such as B–X–B bond angle. Overall, this work provides a science-based generic principle to design the electronic states within the band structure in Cs-based perovskites in presence of point defects such as antisite defect.

scholarly journals Theoretical Study of the Structures of 4-(2,3,5,6-Tetrafluoropyridyl)Diphenylphosphine Oxide and Tris(Pentafluorophenyl)Phosphine Oxide: Why Does the Crystal Structure of (Tetrafluoropyridyl)Diphenylphosphine Oxide Have Two Different P=O Bond Lengths?

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2778
Author(s):  
Joseph R. Lane ◽  
Graham C. Saunders
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Phosphine Oxide ◽  
Density Functional ◽  
Lone Pair ◽  
Diphenylphosphine Oxide ◽  
Functional Theory ◽  
Weak Hydrogen Bonding ◽  
Independent Molecules ◽  
The Difference

The crystal structure of 4-(2,3,5,6-tetrafluoropyridyl)diphenylphosphine oxide (1) contains two independent molecules in the asymmetric unit. Although the molecules are virtually identical in all other aspects, the P=O bond distances differ by ca. 0.02 Å. In contrast, although tris(pentafluorophenyl)phosphine oxide (2) has a similar crystal structure, the P=O bond distances of the two independent molecules are identical. To investigate the reason for the difference, a density functional theory study was undertaken. Both structures comprise chains of molecules. The attraction between molecules of 1, which comprises lone pair–π, weak hydrogen bonding and C–H∙∙∙arene interactions, has energies of 70 and 71 kJ mol−1. The attraction between molecules of 2 comprises two lone pair–π interactions, and has energies of 99 and 100 kJ mol−1. There is weak hydrogen bonding between molecules of adjacent chains involving the oxygen atom of 1. For one molecule, this interaction is with a symmetry independent molecule, whereas for the other, it also occurs with a symmetry related molecule. This provides a reason for the difference in P=O distance. This interaction is not possible for 2, and so there is no difference between the P=O distances of 2.

On the role of steric and exchange–correlation effects in halogenated complexes

2021 ◽  
Author(s):  
Mojtaba Alipour ◽  
Parisa Fallahzadeh
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Partitioning ◽  
Correlation Effects ◽  
Functional Theory ◽  
Exchange Correlation

Density functional theory formalisms of energy partitioning schemes are utilized to find out what energetic components govern interactions in halogenated complexes.

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