Numerical Analysis of Sub-Atomic AFM Imaging in Ultra-High Vacuum: Coupling Quantum Mechanics With Continuum Dynamics

2011 ◽  
Author(s):  
C. Alan Wright ◽  
Santiago D. Solares
Keyword(s):  
Density Functional ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Computational Method ◽  
Tungsten Atom ◽  
Electronic Density ◽  
Functional Theory ◽  
Higher Harmonics ◽  
Afm Imaging ◽  
Continuum Dynamics

Recent reports of sub-atomic resolution AFM images acquired using transition metal tips have sparked debate within the AFM community. However, an in-depth theoretical feasibility study of this work has yet to be produced. We focus on the tungsten/graphite system investigated by Hembacher and coworkers [Science 305, 380–383 (2004)] in which experimental higher-harmonics images revealed four-leaf clover symmetry features within the tungsten atom diameter. The authors interpret these features as the footprint of four bonding lobes of increased charge density at the tip apex atom, thought to be caused by covalent-like bonding in the bulk. Here we present our development of a computational method ranging from density functional theory to continuum dynamics for simulating the imaging process. We find that four lobes of increased electronic density are indeed present for W(001) tips and demonstrate the ability of the chemical forces on the tip apex atom to produce higher harmonics images.

scholarly journals Effect of H Adsorption on the Magnetic Properties of an Fe Island on a W(110) Surface

2019 ◽  
Author(s):  
Marko Melander ◽  
Hannes Jonsson
Keyword(s):  
Magnetic Properties ◽  
Data Storage ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Low Dimensional ◽  
Low Dimensional Materials

<p>Low-dimensional materials, such as ultrathin films, nanoislands and wires, are actively being researched due to their interesting magnetic properties and possible technological applications for example in high density data storage. Results of calculations of an Fe nanoisland on a W(110) support are presented here with particular focus on the effect of hydrogen adsorption on its magnetic properties. This is an important consideration since hydrogen is present even under ultra-high vacuum conditions. The calculations are based on density functional theory within the generalized gradient approximation. The adsorption of H atoms is found to strongly decrease the magnetic moment of the Fe atoms they are bound to, down to less than a half in some cases as compared with the clean Fe island. The results show that it may be important to take the presence of hydrogen into account in measurements of magnetic properties of nanoislands.</p>

scholarly journals Effect of H Adsorption on the Magnetic Properties of an Fe Island on a W(110) Surface

2019 ◽  
Author(s):  
Marko Melander ◽  
Hannes Jonsson
Keyword(s):  
Magnetic Properties ◽  
Data Storage ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Low Dimensional ◽  
Low Dimensional Materials

<p>Low-dimensional materials, such as ultrathin films, nanoislands and wires, are actively being researched due to their interesting magnetic properties and possible technological applications for example in high density data storage. Results of calculations of an Fe nanoisland on a W(110) support are presented here with particular focus on the effect of hydrogen adsorption on its magnetic properties. This is an important consideration since hydrogen is present even under ultra-high vacuum conditions. The calculations are based on density functional theory within the generalized gradient approximation. The adsorption of H atoms is found to strongly decrease the magnetic moment of the Fe atoms they are bound to, down to less than a half in some cases as compared with the clean Fe island. The results show that it may be important to take the presence of hydrogen into account in measurements of magnetic properties of nanoislands.</p>

Investigating the coverage dependent behaviour of CO on Gd/Pt(111)

2016 ◽  
Vol 18 (43) ◽  
pp. 29732-29739 ◽  
Author(s):  
Elisabeth Therese Ulrikkeholm ◽  
Martin Hangaard Hansen ◽  
Jan Rossmeisl ◽  
Ib Chorkendorff
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Functional Theory ◽  
Dependent Behaviour

The coverage dependent behaviour of CO on a strained Pt surface has been studied using in ultra high vacuum and using density functional theory.

First-principles insight into CO hindered agglomeration of Rh and Pt single atoms on ZrO2

2020 ◽  
Author(s):  
Minttu M. Kauppinen ◽  
Marko Melander ◽  
Karoliina Honkala
Keyword(s):  
First Principles ◽  
Density Functional ◽  
High Vacuum ◽  
Kinetic Stability ◽  
Ultra High Vacuum ◽  
Functional Theory ◽  
Single Atoms ◽  
Atomistic Thermodynamics ◽  
Using Data ◽  
Insight Into

<div><div><div><p>In this first-principles study we evaluate the thermodynamic and kinetic stability of Rh and Pt single-atoms (SAs) and subnano clusters on the monoclinic zirconia surface with and without a CO atmosphere. To address the kinetic stability and agglomeration of SAs to clusters and nanoparticles, a non-equilibrium nanothermodynamic approach is developed and parametrised using data computed with density functional theory. The bare subnano clusters are more stable than SA and become more so with increasing size, which means the agglomeration is always favoured. CO binds strongly to the single atoms and clusters, and our atomistic thermodynamics treatment indicates that some CO will be present even at ultra-high vacuum conditions. A CO atmosphere is shown to hinder cluster growth from SA, and is even capable of spontaneous cluster disintegration in the case of Pt clusters. Analysis of the CO stretching frequencies reveals that subnano clusters and single atoms should give peaks in the same region, and that using them to distinguish between surface species requires caution.</p></div></div></div>

First-principles insight into CO hindered agglomeration of Rh and Pt single atoms on ZrO2

2020 ◽  
Author(s):  
Minttu M. Kauppinen ◽  
Marko Melander ◽  
Karoliina Honkala
Keyword(s):  
First Principles ◽  
Density Functional ◽  
High Vacuum ◽  
Kinetic Stability ◽  
Ultra High Vacuum ◽  
Functional Theory ◽  
Single Atoms ◽  
Atomistic Thermodynamics ◽  
Using Data ◽  
Insight Into

<div><div><div><p>In this first-principles study we evaluate the thermodynamic and kinetic stability of Rh and Pt single-atoms (SAs) and subnano clusters on the monoclinic zirconia surface with and without a CO atmosphere. To address the kinetic stability and agglomeration of SAs to clusters and nanoparticles, a non-equilibrium nanothermodynamic approach is developed and parametrised using data computed with density functional theory. The bare subnano clusters are more stable than SA and become more so with increasing size, which means the agglomeration is always favoured. CO binds strongly to the single atoms and clusters, and our atomistic thermodynamics treatment indicates that some CO will be present even at ultra-high vacuum conditions. A CO atmosphere is shown to hinder cluster growth from SA, and is even capable of spontaneous cluster disintegration in the case of Pt clusters. Analysis of the CO stretching frequencies reveals that subnano clusters and single atoms should give peaks in the same region, and that using them to distinguish between surface species requires caution.</p></div></div></div>

Unexpected high binding energy of CO2 on CH3NH3PbI3 lead-halide organic–inorganic perovskites via bicarbonate formation

2018 ◽  
Vol 54 (71) ◽  
pp. 9949-9952 ◽  
Author(s):  
M. T. Nayakasinghe ◽  
Yulun Han ◽  
N. Sivapragasam ◽  
Dmitri S. Kilin ◽  
U. Burghaus
Keyword(s):  
Density Functional Theory ◽  
Binding Energy ◽  
Density Functional ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Binding Energy ◽  
Functional Theory ◽  
Bicarbonate Formation ◽  
Kinetics Of ◽  
Lead Halide

The adsorption kinetics of CO2 was experimentally characterized in ultra-high vacuum (UHV). In addition, density functional theory (DFT) calculations were included.

scholarly journals Nitrile versus isonitrile adsorption at interstellar grain surfaces

2017 ◽  
Vol 608 ◽  
pp. A50 ◽  
Author(s):  
M. Bertin ◽  
M. Doronin ◽  
X. Michaut ◽  
L. Philippe ◽  
A. Markovits ◽  
...  
Keyword(s):  
Density Functional ◽  
Surface Defects ◽  
High Vacuum ◽  
Solid Support ◽  
Ultra High Vacuum ◽  
Structural Defects ◽  
Adsorption Energies ◽  
The Difference ◽  
Temperature Programmed ◽  
Open Question

Context. Almost 20% of the ~200 different species detected in the interstellar and circumstellar media present a carbon atom linked to nitrogen by a triple bond. Of these 37 molecules, 30 are nitrile R-CN compounds, the remaining 7 belonging to the isonitrile R-NC family. How these species behave in their interactions with the grain surfaces is still an open question. Aims. In a previous work, we have investigated whether the difference between nitrile and isonitrile functional groups may induce differences in the adsorption energies of the related isomers at the surfaces of interstellar grains of various nature and morphologies. This study is a follow up of this work, where we focus on the adsorption on carbonaceous aromatic surfaces. Methods. The question is addressed by means of a concerted experimental and theoretical approach of the adsorption energies of CH3CN and CH3NC on the surface of graphite (with and without surface defects). The experimental determination of the molecule and surface interaction energies is carried out using temperature-programmed desorption in an ultra-high vacuum between 70 and 160 K. Theoretically, the question is addressed using first-principle periodic density functional theory to represent the organised solid support. Results. The adsorption energy of each compound is found to be very sensitive to the structural defects of the aromatic carbonaceous surface: these defects, expected to be present in a large numbers and great diversity on a realistic surface, significantly increase the average adsorption energies to more than 50% as compared to adsorption on perfect graphene planes. The most stable isomer (CH3CN) interacts more efficiently with the carbonaceous solid support than the higher energy isomer (CH3NC), however.

Investigation, using density function theory, of coverage of the kaolinite (001) surface during hydrogen adsorption

Clay Minerals ◽  
2018 ◽  
Vol 53 (3) ◽  
pp. 393-402 ◽  
Author(s):  
Jian Zhao ◽  
Wei Gao ◽  
Zhi-Gang Tao ◽  
Hong-Yun Guo ◽  
Man-Chao He
Keyword(s):  
Density Functional ◽  
Hydrogen Adsorption ◽  
Function Theory ◽  
Lattice Relaxation ◽  
Electronic Density ◽  
Functional Theory ◽  
Adsorption Sites ◽  
Coverage Dependence ◽  
Hydrogen Molecules ◽  
Wide Range

ABSTRACTKaolinite can be used for many applications, including the underground storage of gases. Density functional theory was employed to investigate the adsorption of hydrogen molecules on the kaolinite (001) surface. The coverage dependence of the adsorption sites and energetics was studied systematically for a wide range of coverage, Θ (from 1/16 to 1 monolayer). The three-fold hollow site is the most stable, followed by the bridge, top-z and top sites. The adsorption energy of H2 decreased with increasing coverage, thus indicating the lower stability of surface adsorption due to the repulsion of neighbouring H2 molecules. The coverage has obvious effects on hydrogen adsorption. Other properties of the H2/kaolinite (001) system, including the lattice relaxation and changes of electronic density of states, were also studied and are discussed in detail.

scholarly journals Towards a density functional theory of molecular fragments. What is the shape of atoms in molecules?

2020 ◽  
Vol 44 (170) ◽  
pp. 269-279
Author(s):  
Victor H. Chávez ◽  
Adam Wasserman
Keyword(s):  
Density Functional Theory ◽  
Schrödinger Equation ◽  
Schrodinger Equation ◽  
Density Functional ◽  
Computational Cost ◽  
Atoms In Molecules ◽  
Electronic Density ◽  
Functional Theory ◽  
New Methods ◽  
The Cost

In some sense, quantum mechanics solves all the problems in chemistry: The only thing one has to do is solve the Schrödinger equation for the molecules of interest. Unfortunately, the computational cost of solving this equation grows exponentially with the number of electrons and for more than ~100 electrons, it is impossible to solve it with chemical accuracy (~ 2 kcal/mol). The Kohn-Sham (KS) equations of density functional theory (DFT) allow us to reformulate the Schrödinger equation using the electronic probability density as the central variable without having to calculate the Schrödinger wave functions. The cost of solving the Kohn-Sham equations grows only as N3, where N is the number of electrons, which has led to the immense popularity of DFT in chemistry. Despite this popularity, even the most sophisticated approximations in KS-DFT result in errors that limit the use of methods based exclusively on the electronic density. By using fragment densities (as opposed to total densities) as the main variables, we discuss here how new methods can be developed that scale linearly with N while providing an appealing answer to the subtitle of the article: What is the shape of atoms in molecules?

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