scholarly journals What is the origin of macroscopic friction?

2018 ◽  
Vol 4 (12) ◽  
pp. eaav2268 ◽  
Author(s):  
H. Sakuma ◽  
K. Kawai ◽  
I. Katayama ◽  
S. Suehara
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Wear Particles ◽  
Shear Tests ◽  
Functional Theory ◽  
Direct Shear Tests ◽  
Sliding Direction ◽  
Frictional Forces ◽  
Experimental Findings ◽  
Molecular Friction

What is the origin of molecular friction, and how can macroscopic friction be explained in terms of molecular friction? To elucidate the origins of molecular and macroscopic friction, we conducted density functional theory calculations and double-direct shear tests at normal stresses ranging from 5 to 60 MPa for mica surfaces. Frictional forces between mica surfaces were theoretically predicted to oscillate periodically every 30° of sliding direction, in agreement with previous experimental findings. This result affirms that the potential energy roughness of mica under sliding is the origin of molecular friction, which depends on the normal stress and sliding direction. The discovered mechanism of molecular friction can quantitatively explain experimentally observed macroscopic friction of mica when the presence of wear particles is taken into consideration.

scholarly journals Relative Stability of Small Silver, Platinum, and Palladium Doped Gold Cluster Cations

2019 ◽  
Vol 9 (8) ◽  
pp. 1666 ◽  
Author(s):  
Piero Ferrari ◽  
Ewald Janssens
Keyword(s):  
Density Functional ◽  
Gold Cluster ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Local Maxima ◽  
Dissociation Energies ◽  
Valence Electrons ◽  
Pd Doping ◽  
The Stability ◽  
Experimental Findings

The stability patterns of single silver, platinum, and palladium atom doped gold cluster cations, MAuN−1+ (M = Ag, Pt, Pd; N = 3–6), are investigated by a combination of photofragmentation experiments and density functional theory calculations. The mass spectra of the photofragmented clusters reveal an odd-even pattern in the abundances of AgAuN−1+, with local maxima for clusters containing an even number of valence electrons, similarly to pure AuN+. The odd-even pattern, however, disappears upon Pt and Pd doping. Computed dissociation energies agree well with the experimental findings for the different doped clusters. The effect of Ag, Pt, and Pd doping is discussed on the basis of an analysis of the density of states of the N = 3–5 clusters. Whereas Ag delocalizes its 5s valence electron in all sizes, this process is size-specific for Pt and Pd.

scholarly journals Structural model of silicene-like nanoribbons on a Pb-reconstructed Si(111) surface

2017 ◽  
Vol 8 ◽  
pp. 1836-1843 ◽  
Author(s):  
Agnieszka Stępniak-Dybala ◽  
Mariusz Krawiec
Keyword(s):  
Density Functional Theory ◽  
Surface Energy ◽  
First Principles ◽  
Density Functional ◽  
Structural Model ◽  
Density Functional Theory Calculations ◽  
Honeycomb Structure ◽  
Functional Theory ◽  
Substrate Interaction ◽  
Experimental Findings

A structural model of the recently observed silicene-like nanoribbons on a Pb-induced √3 × √3 reconstructed Si(111) surface is proposed. The model, which is based on first principles density functional theory calculations, features a deformed honeycomb structure directly bonded to the Si(111) surface underneath. Pb atoms stabilize the nanoribbons, as they passivate the uncovered substrate, thus lower the surface energy, and suppress the nanoribbon–substrate interaction. The proposed structural model reproduces well all the experimental findings.

Tribological properties of a series of carbon dots modified by ionic liquids with various anion species: experimental findings and density functional theory calculations

2021 ◽  
Author(s):  
Baogang Wang ◽  
Lilong Zhang ◽  
Na Wang ◽  
Wenmeng Duan ◽  
Weiwei Tang
Keyword(s):  
Ionic Liquids ◽  
Carbon Dots ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
One Pot ◽  
Functional Theory ◽  
Exchange Processes ◽  
The One ◽  
Experimental Findings ◽  
Anion Species

A series of carbon dots modified by ionic liquids with various anion species (CDs-ILs-X) were facile synthesized by the one-pot pyrolysis method and subsequent anion exchange processes, where the X-...

From HCOOH to CO on Pd catalyst: theoretical study

2017 ◽  
Vol 95 (10) ◽  
pp. 1081-1084 ◽  
Author(s):  
Yingying Wang ◽  
Zijiao Chen
Keyword(s):  
Density Functional Theory ◽  
Formic Acid ◽  
Density Functional ◽  
Theoretical Study ◽  
Density Functional Theory Calculations ◽  
Experimental Results ◽  
Pd Catalyst ◽  
Co Poisoning ◽  
Functional Theory ◽  
Experimental Findings

The present theoretical and experimental results in the literature for formic acid (HCOOH) oxidation into CO on Pd(111) cannot rationalize the well-known, easy CO poisoning. The present study reexamines HCOOH oxidation on Pd(111) by performing density functional theory calculations. Upon a thorough search, we present a new adsorption configuration of HCOOH on Pd(111). From the calculated energy pathway, we proposed that CO arises from the reduction of the hydrogenation product CO2 and direct dehydration of formic acid during HCOOH oxidation on Pd(111), with latter step being energetically easier. The present theoretical study rationalizes the early experimental findings and provides insights into the deactivation problem of Pd catalyst in the process of HCOOH oxidation.

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

2019 ◽  
Author(s):  
Hassan Harb ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Triple Bond ◽  
Density Functional ◽  
Valence Electron ◽  
Density Functional Theory Calculations ◽  
Electron Configuration ◽  
Functional Theory ◽  
Key Species ◽  
Pi Orbitals ◽  
Lanthanide Hydroxide ◽  
Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

2019 ◽  
Author(s):  
Hassan Harb ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Triple Bond ◽  
Density Functional ◽  
Valence Electron ◽  
Density Functional Theory Calculations ◽  
Electron Configuration ◽  
Functional Theory ◽  
Key Species ◽  
Pi Orbitals ◽  
Lanthanide Hydroxide ◽  
Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

A New Interpretation of the Structure and Solvent Dependence of the Far UV Circular Dichroism Spectrum of Short Oligopeptides

2019 ◽  
Author(s):  
Anshuman Kumar ◽  
Reinhard Schweitzer-Stenner ◽  
Bryan Wong
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Cd Spectra ◽  
Functional Theory ◽  
Polyproline Ii ◽  
Solvent Dependence ◽  
Explicit Consideration ◽  
New Interpretation ◽  
Implicit And Explicit ◽  
Explicit Water

In this work, we carry out new time-dependent density functional theory calculations on the cationic tripeptide GAG in implicit and explicit water to determine the transitions that give rise to the observed CD signals of polyproline II and β-strand conformations. Our results reveal a plethora of electronic transitions that are governed by configurational interactions between multiple molecular orbital transitions of comparable energy. We also show that reproducing the CD spectra of polyproline II and β-strand conformations requires the explicit consideration of water molecules. The structure dependence of delocalized occupied orbitals contributes to the experimentally-observed invalidation of Flory’s isolated pair hypothesis.

A New Interpretation of the Structure and Solvent Dependence of the Far UV Circular Dichroism Spectrum of Short Oligopeptides

2019 ◽  
Author(s):  
Anshuman Kumar ◽  
Reinhard Schweitzer-Stenner ◽  
Bryan Wong
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Cd Spectra ◽  
Functional Theory ◽  
Polyproline Ii ◽  
Solvent Dependence ◽  
Explicit Consideration ◽  
New Interpretation ◽  
Implicit And Explicit ◽  
Explicit Water

In this work, we carry out new time-dependent density functional theory calculations on the cationic tripeptide GAG in implicit and explicit water to determine the transitions that give rise to the observed CD signals of polyproline II and β-strand conformations. Our results reveal a plethora of electronic transitions that are governed by configurational interactions between multiple molecular orbital transitions of comparable energy. We also show that reproducing the CD spectra of polyproline II and β-strand conformations requires the explicit consideration of water molecules. The structure dependence of delocalized occupied orbitals contributes to the experimentally-observed invalidation of Flory’s isolated pair hypothesis.

Is a Non-Transition Element Nitride Ferromagnet Ever Achievable? Indication of the N-N Pairing Instability

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1525-1531 ◽  
Author(s):  
Wojciech Grochala
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Transition Element ◽  
Density Functional Theory Calculations ◽  
Functional Theory

The enthalpy of four polymorphs of CaN has been scrutinized at 0 and 100 GPa using density functional theory calculations. It is shown that structures of diamagnetic calcium diazenide (Ca2N2) are preferred over the cubic ferromagnetic polymorph (CaN) postulated before, both at 0 and 100 GPa.

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