51
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Bhattacharya SK, Deodhar PA, Viswanatha R, Kshirsagar A. Transferable orthogonal tight-binding parameters for ZnS and CdS. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:295304. [PMID: 21399300 DOI: 10.1088/0953-8984/22/29/295304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Calculations of Slater-Koster (SK) parameters appearing in the tight-binding method using sp(3)d(5) basis sets for both the cationic and anionic species are presented for ZnS and CdS. We have adjusted these parameters to match the band structures obtained from the full potential linear augmented plane wave method. This operation has been carried out for a variety of structures namely zinc blende, wurtzite, rocksalt, CsCl and for a wide range of near-neighbor distances. The SK parameters have slightly different values for the same near-neighbor distance in different structures. Therefore, a least-squares fitting has been performed separately for each parameter as a function of only the near-neighbor distance to guarantee the transferability of these parameters to different structural environments. The fitted parameters are then used to calculate the electronic structure of small-sized clusters of ZnS and CdS in given geometries and the results are compared with ab initio results. A fairly good agreement found in the one-electron energy spectrum and total energy confirms transferability of the parameters to different length scales. A detailed account of the calculation procedure and calibration results is given in the present paper. These parameters can be used to study the electronic structure of large-sized clusters where first-principles methods are computationally demanding. It may be mentioned that the SK parameters do not satisfy the R(-(l + l' + 1)) Harrison scaling law for larger values of the near-neighbor distance R.
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52
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Soulairol R, Fu CC, Barreteau C. Structure and magnetism of bulk Fe and Cr: from plane waves to LCAO methods. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:295502. [PMID: 21399309 DOI: 10.1088/0953-8984/22/29/295502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Magnetic, structural and energetic properties of bulk Fe and Cr were studied using first-principles calculations within density functional theory (DFT). We aimed to identify the dependence of these properties on key approximations of DFT, namely the exchange-correlation functional, the pseudopotential and the basis set. We found a smaller effect of pseudopotentials (PPs) on Fe than on Cr. For instance, the local magnetism of Cr was shown to be particularly sensitive to the potentials representing the core electrons, i.e. projector augmented wave and Vanderbilt ultrasoft PPs predict similar results, whereas standard norm-conserving PPs tend to overestimate the local magnetic moments of Cr in bcc Cr and in dilute bcc FeCr alloys. This drawback is suggested to be closely correlated to the overestimation of Cr solution energy in the latter system. On the other hand, we point out that DFT methods with very reduced localized basis sets (LCAO: linear combination of atomic orbitals) give satisfactory results compared with more robust plane-wave approaches. A minimal-basis representation of '3d' electrons comes to be sufficient to describe non-trivial magnetic phases including spin spirals in both fcc Fe and bcc Cr, as well as the experimental magnetic ground state of bcc Cr showing a spin density wave (SDW) state. In addition, a magnetic 'spd' tight binding model within the Stoner formalism was proposed and validated for Fe and Cr. The respective Stoner parameters were obtained by fitting to DFT data. This efficient semiempirical approach was shown to be accurate enough for studying various collinear and non-collinear phases of bulk Fe and Cr. It also enabled a detailed investigation of different polarization states of SDW in bcc Cr, where the longitudinal state was suggested to be the ground state, consistent with existing experimental data.
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Affiliation(s)
- R Soulairol
- CEA, DEN, Service de Recherches de Métallurgie Physique, Gif-sur-Yvette, France
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53
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Ediz V, Monda AC, Brown RP, Yaron DJ. Using Molecular Similarity to Develop Reliable Models of Chemical Reactions in Complex Environments. J Chem Theory Comput 2009; 5:3175-84. [DOI: 10.1021/ct9004195] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Volkan Ediz
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
| | - Anthony C. Monda
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
| | - Robert P. Brown
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
| | - David J. Yaron
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
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54
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Akdim B, Papaconstantopoulos DA, Mehl MJ. Tight-binding description of the electronic structure and total energy of tin. ACTA ACUST UNITED AC 2009. [DOI: 10.1080/13642810208211215] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Brahim Akdim
- a lnstitute for Computational Sciences and Informatics, George Mason University , Fairfax, Virginia , 22030 , USA
- c Ohio Supercomputer Center , Columbus , Ohio , 43212 , USA
| | - D. A. Papaconstantopoulos
- b Center for Computational Materials Science, Naval Research Laboratory , Washington, DC 20375-5345, USA
| | - M. J. Mehl
- b Center for Computational Materials Science, Naval Research Laboratory , Washington, DC 20375-5345, USA
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55
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Hoshi T, Fujiwara T. Domain boundary formation in helical multishell gold nanowires. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:272201. [PMID: 21828482 DOI: 10.1088/0953-8984/21/27/272201] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Helical multishell gold nanowires are studied theoretically for the formation mechanism of the helical domain boundary. Nanowires with a wire length of more than 10 nm are relaxed by quantum mechanical molecular dynamics simulation with a tight-binding form Hamiltonian. In the results, non-helical nanowires are transformed into helical ones with the formation of atom pair defects at the domain boundary, where the defective atom pair is moved from an inner shell. Analysis of local electronic structure shows a competitive feature of the energy gain of reconstruction on the wire surface and the energy loss of the defect formation. A simple energy scaling theory gives a general explanation of domain boundary formation.
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Affiliation(s)
- T Hoshi
- Department of Applied Mathematics and Physics, Tottori University, Tottori 680-8550, Japan. Core Research for Evolutional Science and Technology, Japan Science and Technology Agency (CREST-JST), Japan
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56
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Patrick AD, Dong X, Allison TC, Blaisten-Barojas E. Silicon carbide nanostructures: a tight binding approach. J Chem Phys 2009; 130:244704. [PMID: 19566171 DOI: 10.1063/1.3157282] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A tight-binding model Hamiltonian is newly parametrized for silicon carbide based on fits to a database of energy points calculated within the density functional theory approach of the electronic energy surfaces of nanoclusters and the total energy of bulk 3C and 2H polytypes at different densities. This TB model includes s and p angular momentum symmetries with nonorthogonal atomic basis functions. With the aid of the new TB model, minima of silicon carbide cagelike clusters, nanotubes, ring-shaped ribbons, and nanowires are predicted. Energetics, structure, growth sequences, and stability patterns are reported for the nanoclusters and nanotubes. The band structure of SiC nanotubes and nanowires indicates that the band gap of the nanotubes ranges from 0.57 to 2.38 eV depending on the chirality, demonstrating that these nanotubes are semiconductors or insulators. One type of nanowire is metallic, another type is semiconductor, and the rest are insulators.
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Affiliation(s)
- Anthony D Patrick
- Computational Materials Science Center, George Mason University, 4400 University Dr. MSN 6A2, Fairfax, Virginia 22030, USA
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57
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Zhao M, Iron MA, Staszewski P, Schultz NE, Valero R, Truhlar DG. Valence–Bond Order (VBO): A New Approach to Modeling Reactive Potential Energy Surfaces for Complex Systems, Materials, and Nanoparticles. J Chem Theory Comput 2009; 5:594-604. [DOI: 10.1021/ct8004535] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Meiyu Zhao
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
| | - Mark A. Iron
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
| | - Przemysław Staszewski
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
| | - Nathan E. Schultz
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
| | - Rosendo Valero
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
| | - Donald G. Truhlar
- Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, and Department of Theoretical Foundations of Biomedical Sciences and Medical Informatics, Collegium Medicum, Nicolaus Copernicus University, ul. Jagiellońska 13, 85-067 Bydgoszcz, Poland
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58
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Liu X, Feldman JL, Cahill DG, Crandall RS, Bernstein N, Photiadis DM, Mehl MJ, Papaconstantopoulos DA. High thermal conductivity of a hydrogenated amorphous silicon film. PHYSICAL REVIEW LETTERS 2009; 102:035901. [PMID: 19257371 DOI: 10.1103/physrevlett.102.035901] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Indexed: 05/27/2023]
Abstract
We measured the thermal conductivity kappa of an 80 microm thick hydrogenated amorphous silicon film prepared by hot-wire chemical-vapor deposition with the 3omega (80-300 K) and the time-domain thermo-reflectance (300 K) methods. The kappa is higher than any of the previous temperature dependent measurements and shows a strong phonon mean free path dependence. We also applied a Kubo based theory using a tight-binding method on three 1000 atom continuous random network models. The theory gives higher kappa for more ordered models, but not high enough to explain our results, even after extrapolating to lower frequencies with a Boltzmann approach. Our results show that this material is more ordered than any amorphous silicon previously studied.
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Affiliation(s)
- Xiao Liu
- Naval Research Laboratory, Washington, DC 20375, USA
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59
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Amorim EPM, da Silva EZ. Helical [110] gold nanowires make longer linear atomic chains. PHYSICAL REVIEW LETTERS 2008; 101:125502. [PMID: 18851385 DOI: 10.1103/physrevlett.101.125502] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Indexed: 05/26/2023]
Abstract
Quantum mechanical molecular dynamics shows that gold nanowires formed along the [110] direction reconstruct upon stress to form helical nanowires. The mechanism for this formation is discussed. These helical nanowires evolve on stretching to form linear atomic chains. Because helical nanowires do not form symmetrical tips, a requirement to stop the growth of atomic chains, these nanowires produce longer atomic chains than other nanowires. These results are obtained resorting to the use of tight-binding molecular dynamics and ab initio electronic structure calculations.
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Affiliation(s)
- E P M Amorim
- Institute of Physics Gleb Wataghin, University of Campinas-Unicamp, Campinas, São Paulo, Brazil
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60
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Leoni T, Zoubkoff R, Homri S, Candoni N, Vidakovic P, Ranguis A, Klein H, Saúl A, Dumas P. Are conductance plateaus independent events in atomic point contact measurements? A statistical approach. NANOTECHNOLOGY 2008; 19:355401. [PMID: 21828849 DOI: 10.1088/0957-4484/19/35/355401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Conductance-elongation curves of gold atomic wires are measured using a scanning tunneling microscope break junction technique at room temperature. Landauer's conductance plateaus are individually identified and statistically analyzed. Both the probabilities to observe and the lengths of the two last plateaus (at conductance values close to 2e(2)/h and 4e(2)/h) are studied. All results converge to show that the occurrences of these two conductance plateaus on a conductance-elongation curve are statistically independent events.
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Affiliation(s)
- Thomas Leoni
- CINaM-CNRS 3118, Aix-Marseille Université, Faculté de Luminy, Case 913, 13288, Marseille Cedex, France
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61
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Rincón L, Hasmy A, Gonzalez CA, Almeida R. Extended Hückel tight-binding approach to electronic excitations. J Chem Phys 2008; 129:044107. [DOI: 10.1063/1.2956489] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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62
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Iguchi Y, Hoshi T, Fujiwara T. Two-stage formation model and helicity of gold nanowires. PHYSICAL REVIEW LETTERS 2007; 99:125507. [PMID: 17930520 DOI: 10.1103/physrevlett.99.125507] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Indexed: 05/25/2023]
Abstract
A model for the formation of helical multishell gold nanowires is proposed and is confirmed with quantum mechanical molecular dynamics simulations. The model can explain the magic number of the helical gold nanowires in the multishell structure. The reconstruction from ideal nonhelical to realistic helical nanowires consists of two stages: dissociations of atoms on the outermost shell from atoms on the inner shell and slip deformations of atom rows generating (111)-like structure on the outermost shell. The elementary processes are governed by competition between energy loss and gain by s and d electrons together with the width of the d band. The possibility for the helical nanowires of platinum, silver, and copper is discussed.
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Affiliation(s)
- Yusuke Iguchi
- Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo, 113-8656, Japan
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63
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Haskins RW, Maier RS, Ebeling RM, Marsh CP, Majure DL, Bednar AJ, Welch CR, Barker BC, Wu DT. Tight-binding molecular dynamics study of the role of defects on carbon nanotube moduli and failure. J Chem Phys 2007; 127:074708. [PMID: 17718628 DOI: 10.1063/1.2756832] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We performed tight-binding molecular dynamics on single-walled carbon nanotubes with and without a variety of defects to study their effect on the nanotube modulus and failure through bond rupture. For a pristine (5,5) nanotube, Young's modulus was calculated to be approximately 1.1 TPa, and brittle rupture occurred at a strain of 17% under quasistatic loading. The predicted modulus is consistent with values from experimentally derived thermal vibration and pull test measurements. The defects studied consist of moving or removing one or two carbon atoms, and correspond to a 1.4% defect density. The occurrence of a Stone-Wales defect does not significantly affect Young's modulus, but failure occurs at 15% strain. The occurrence of a pair of separated vacancy defects lowers Young's modulus by approximately 160 GPa and the critical or rupture strain to 13%. These defects apparently act independently, since one of these defects alone was independently determined to lower Young's modulus by approximately 90 GPa, also with a critical strain of 13%. When the pair of vacancy defects adjacent, however, Young's modulus is lowered by only approximately 100 GPa, but with a lower critical strain of 11%. In all cases, there is noticeable strain softening, for instance, leading to an approximately 250 GPa drop in the apparent secant modulus at 10% strain. When a chiral (10,5) nanotube with a vacancy defect was subjected to tensile strain, failure occurred through a continuous spiral-tearing mechanism that maintained a high level of stress (2.5 GPa) even as the nanotube unraveled. Since the statistical likelihood of defects occurring near each other increases with nanotube length, these studies may have important implications for interpreting the experimental distribution of moduli and critical strains.
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Affiliation(s)
- Richard W Haskins
- U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi 39180-6133, USA.
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64
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Wang JS, Zeng N, Wang J, Gan CK. Nonequilibrium Green's function method for thermal transport in junctions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:061128. [PMID: 17677241 DOI: 10.1103/physreve.75.061128] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Indexed: 05/16/2023]
Abstract
We present a detailed treatment of the nonequilibrium Green's function method for thermal transport due to atomic vibrations in nanostructures. Some of the key equations, such as self-energy and conductance with nonlinear effect, are derived. A self-consistent mean-field theory is proposed. Computational procedures are discussed. The method is applied to a number of systems including one-dimensional chains, a benzene ring junction, and carbon nanotubes. Mean-field calculations of the Fermi-Pasta-Ulam model are compared with classical molecular dynamics simulations using a generalized Langevin heat bath. We find that nonlinearity suppresses thermal transport even at moderately high temperatures.
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Affiliation(s)
- Jian-Sheng Wang
- Center for Computational Science and Engineering, and Department of Physics, National University of Singapore, Singapore 117542, USA
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65
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66
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Silva E, Novaes FD, Silva A, Fazzio A. Gold nanowires and the effect of impurities. NANOSCALE RESEARCH LETTERS 2006; 1:91. [PMCID: PMC3246670 DOI: 10.1007/s11671-006-9018-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Metal nanowires and in particular gold nanowires have received a great deal of attention in the past few years. Experiments on gold nanowires have prompted theory and simulation to help answer questions posed by these studies. Here we present results of computer simulations for the formation, evolution and breaking of very thin Au nanowires. We also discuss the influence of contaminants, such as atoms and small molecules, and their effect on the structural and mechanical properties of these nanowires.
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Affiliation(s)
- EdisonZda Silva
- Instituto de Física “Gleb Wataghin”, UNICAMP, CP 6165, 13083-970, Campinas, SP, Brazil
| | | | - AntônioJRda Silva
- Instituto de Física, USP, CP 66318, 05315-970, São Paulo, SP, Brazil
| | - A Fazzio
- Instituto de Física, USP, CP 66318, 05315-970, São Paulo, SP, Brazil
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67
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Fyta MG, Remediakis IN, Kelires PC, Papaconstantopoulos DA. Insights into the fracture mechanisms and strength of amorphous and nanocomposite carbon. PHYSICAL REVIEW LETTERS 2006; 96:185503. [PMID: 16712372 DOI: 10.1103/physrevlett.96.185503] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2005] [Indexed: 05/09/2023]
Abstract
Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs intergrain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.
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Affiliation(s)
- M G Fyta
- Physics Department, University of Crete, P.O. Box 2208, 71003 Heraclion, Crete, Greece
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68
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Gross A, Eichler A, Hafner J, Mehl MJ, Papaconstantopoulos DA. Ab initio based tight-binding molecular dynamics simulation of the sticking and scattering of O2∕Pt(111). J Chem Phys 2006; 124:174713. [PMID: 16689596 DOI: 10.1063/1.2192512] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The sticking and scattering of O(2)Pt(111) has been studied by tight-binding molecular dynamics simulations based on an ab initio potential energy surface. We focus, in particular, on the sticking probability as a function of the angle of incidence and the energy and angular distributions in scattering. Our simulations provide an explanation for the seemingly paradox experimental findings that adsorption experiments suggest that the O(2)Pt(111) interaction potential should be strongly corrugated while scattering experiments indicate a rather small corrugation. The potential energy surface is indeed strongly corrugated which leads to a pronounced dependence of the sticking probability on the angle of incidence. The scattered O(2) molecules, however, experience a rather flat surface due to the fact that they are predominantly scattered at the repulsive tail of the potential.
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Affiliation(s)
- A Gross
- Abteilung Theoretische Chemie, Universität Ulm, D-89069 Ulm, Germany.
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69
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Zhuang M, Rocheleau P, Ernzerhof M. Approximate density functionals applied to molecular quantum dots. J Chem Phys 2005; 122:154705. [PMID: 15945654 DOI: 10.1063/1.1878632] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Recently, molecular quantum dots (MQDs) have been investigated experimentally and found to exhibit the Kondo effect. The Kondo effect leads to an enhancement of the zero-voltage conductance. Here, we study a finite cluster model of a MQD by means of Kohn-Sham density functional theory. Furthermore, employing an implementation of Landauer's formula, we calculate the conductance of the dot. We find that the electronic structure and the molecular conductance depend strongly on the exchange-correlation functional employed. While the local spin density approximation and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation qualitatively reproduce certain features of the Kondo effect, PBE hybrid does not. Based on the MQD, we discuss the limitations of using density functional theory to model molecular electronic devices.
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Affiliation(s)
- Min Zhuang
- Département de Chimie, Université de Montréal, C.P. 6128 Succursale A, Montréal, Québec H3C 3J7, Canada
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70
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Pergolese B, Bigotto A, Muniz-Miranda M, Sbrana G. Gold/palladium and silver/palladium colloids as novel metallic substrates for surface-enhanced Raman scattering. APPLIED SPECTROSCOPY 2005; 59:194-199. [PMID: 15720760 DOI: 10.1366/0003702053085034] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
New surface-enhanced Raman scattering (SERS) substrates, composed of gold or silver colloidal nanoparticles doped with palladium, were prepared. These novel colloids are stable and maintain a satisfactory SERS efficiency, even after long aging. The interest in doping the coinage metal nanoparticles with palladium is due to the well-known catalytic activity of this metal. Transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize the shape and size of the metal particles. It was found that these bimetallic colloidal nanoparticles have a core-shell structure, with gold or silver coated with palladium clusters.
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Affiliation(s)
- Barbara Pergolese
- Department of Chemical Sciences, University of Trieste, Trieste, I-34127 Italy.
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71
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Janesko BG, Yaron D. Using molecular similarity to construct accurate semiempirical electronic structure theories. J Chem Phys 2004; 121:5635-45. [PMID: 15366987 DOI: 10.1063/1.1785771] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Ab initio electronic structure methods give accurate results for small systems, but do not scale well to large systems. Chemical insight tells us that molecular functional groups will behave approximately the same way in all molecules, large or small. This molecular similarity is exploited in semiempirical methods, which couple simple electronic structure theories with parameters for the transferable characteristics of functional groups. We propose that high-level calculations on small molecules provide a rich source of parametrization data. In principle, we can select a functional group, generate a large amount of ab initio data on the group in various small-molecule environments, and "mine" this data to build a sophisticated model for the group's behavior in large environments. This work details such a model for electron correlation: a semiempirical, subsystem-based correlation functional that predicts a subsystem's two-electron density matrix as a functional of its one-electron density matrix. This model is demonstrated on two small systems: chains of linear, minimal-basis (H-H)(5), treated as a sum of four overlapping (H-H)(2) subsystems; and the aldehyde group of a set of HOC-R molecules. The results provide an initial demonstration of the feasibility of the approach.
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Affiliation(s)
- Benjamin G Janesko
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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72
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Emery SB, Hubbley JL, Roy D. Voltammetric and amperometric analyses of electrochemical nucleation: electrodeposition of copper on nickel and tantalum. J Electroanal Chem (Lausanne) 2004. [DOI: 10.1016/j.jelechem.2004.01.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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73
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Schultz NE, Staszewska G, Staszewski P, Truhlar DG. Validation of Theoretical Methods for the Structure and Energy of Aluminum Clusters. J Phys Chem B 2004. [DOI: 10.1021/jp0370223] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Nathan E. Schultz
- Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431
| | - Grażyna Staszewska
- Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431
| | - Przemysław Staszewski
- Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431
| | - Donald G. Truhlar
- Department of Chemistry and Supercomputer Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431
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Abstract
Using the Landauer formula, the conductance of short gold wires is studied. The required electronic structure calculations are performed with a self-consistent tight-binding method. We consider gold wires of single-atom diameter with a variable number (N=1, em leader,5) of atoms. Depending on N, we find considerable conductance variations with one conductance quantum being the upper limit. The results are confirmed by means of Friedel's sum rule. Tip-shaped clusters are used to provide the contact-wire interfaces and the relation between various tip structures and the conductance is discussed. Our predictions about the conductance variations agree qualitatively with new experimental results.
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Affiliation(s)
- Min Zhuang
- Departement de Chimie, Universite de Montreal, C.P. 6128 Succursale A, Montreal, Quebec, H3C 3J7 Canada
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75
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Trinkle DR, Hennig RG, Srinivasan SG, Hatch DM, Jones MD, Stokes HT, Albers RC, Wilkins JW. New mechanism for the alpha to omega martensitic transformation in pure titanium. PHYSICAL REVIEW LETTERS 2003; 91:025701. [PMID: 12906490 DOI: 10.1103/physrevlett.91.025701] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2003] [Indexed: 05/24/2023]
Abstract
We propose a new direct mechanism for the pressure driven alpha-->omega martensitic transformation in pure titanium. A systematic algorithm enumerates all possible pathways whose energy barriers are evaluated. A new, homogeneous pathway emerges with a barrier at least 4 times lower than other pathways. The pathway is shown to be favorable in any nucleation model.
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Affiliation(s)
- D R Trinkle
- The Ohio State University, Columbus, Ohio 43210, USA
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76
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Hou JG, Wang B, Yang J, Wang K, Lu W, Li Z, Wang H, Chen DM, Zhu Q. Disorder and suppression of quantum confinement effects in Pd nanoparticles. PHYSICAL REVIEW LETTERS 2003; 90:246803. [PMID: 12857212 DOI: 10.1103/physrevlett.90.246803] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2002] [Indexed: 05/24/2023]
Abstract
Size-selectable ligand-passivated crystalline and amorphous Pd nanoparticles (<4 nm) are synthesized by a novel two-phase process and verified by high-resolution transmission electron microscopy. Scanning tunneling spectroscopy preformed at 5 K on these two types of nanoparticles exhibits clear Coulomb blockade and Coulomb staircases. Size dependent multipeak spectral features in the differential conductance curve are observed for the crystalline Pd particles but not for the amorphous particles. Theoretical analysis shows that these spectral features are related to the quantized electronic states in the crystalline Pd particle. The suppression of the quantum confinement effect in the amorphous particle arises from the reduction of the degeneracy of the eigenstates and the level broadening due to the reduced lifetime of the electronic states.
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Affiliation(s)
- J G Hou
- Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
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77
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Lukatsky DB, Haran G, Safran SA. Slow fluctuations in enhanced Raman scattering and surface roughness relaxation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:062402. [PMID: 16241279 DOI: 10.1103/physreve.67.062402] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2003] [Indexed: 05/04/2023]
Abstract
We propose an explanation for the recently measured slow fluctuations and "blinking" in the surface-enhanced Raman scattering spectrum of single molecules adsorbed on a silver colloidal particle. We suggest that these fluctuations may be related to the dynamic relaxation of the surface roughness on the nanometer scale and show that there are two classes of roughness with qualitatively different dynamics. The predictions agree with the measurements of surface roughness relaxation. Using a theoretical model for the kinetics of surface roughness relaxation in the presence of charges and optical electrical fields, we predict that the high-frequency electromagnetic field increases both the effective surface tension and the surface diffusion constant and thus accelerates the surface smoothing kinetics and time scale of the Raman fluctuations in a manner that is linear with the laser power intensity, while the addition of salt retards the surface relaxation kinetics and increases the time scale of the fluctuations. These predictions are in qualitative agreement with the Raman experiments.
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Affiliation(s)
- D B Lukatsky
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel.
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78
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Lee S, Hoffmann R. Bcc and Fcc transition metals and alloys: a central role for the Jahn-Teller effect in explaining their ideal and distorted structures. J Am Chem Soc 2002; 124:4811-23. [PMID: 11971731 DOI: 10.1021/ja0114557] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Transition metal elements, alloys, and intermetallic compounds often adopt the body centered cubic (bcc) and face centered cubic (fcc) structures. By comparing quantitative density functional with qualitative tight-binding calculations, we analyze the electronic factors which make the bcc and fcc structures energetically favorable. To do so, we develop a tight-binding function, DeltaE(star), a function that measures the energetic effects of transferring electrons within wave vector stars. This function allows one to connect distortions in solids to the Jahn-Teller effect in molecules and to provide an orbital perspective on structure determining deformations in alloys. We illustrate its use by considering first a two-dimensional square net. We then turn to three-dimensional fcc and bcc structures, and distortions of these. Using DeltaE(star), we rationalize the differences in energy of these structures. We are able to deduce which orbitals are responsible for instabilities in seven to nine valence electron per atom (e(-)/a) bcc systems and five and six e(-)/a fcc structures. Finally we demonstrate that these results account for the bcc and fcc type structures found in both the elements and binary intermetallic compounds of group 4 through 9 transition metal atoms. The outline of a theory of metal structure deformations based on loss of point group operation rather than translational symmetry is presented.
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Affiliation(s)
- Stephen Lee
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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79
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Kumar V, Esfarjani K, Kawazoe Y. Ab Initio Computer Simulations on Microclusters: Structures and Electronic Properties. ACTA ACUST UNITED AC 2002. [DOI: 10.1007/978-3-662-04812-2_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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80
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Vitos L, Abrikosov IA, Johansson B. Anisotropic lattice distortions in random alloys from first-principles theory. PHYSICAL REVIEW LETTERS 2001; 87:156401. [PMID: 11580714 DOI: 10.1103/physrevlett.87.156401] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2001] [Indexed: 05/23/2023]
Abstract
Within the framework of the exact muffin-tin orbitals (EMTO) theory we have developed a new method to calculate the total energy for random substitutional alloys. The problem of disorder is treated within the coherent potential approximation (CPA), and the total energy is obtained using the full charge density (FCD) technique. The FCD-EMTO-CPA method is suitable for determination of energy changes due to anisotropic lattice distortions in random alloys. In particular, we calculate the elastic constants of the Cu-rich face centered cubic Cu-Zn alloys ( alpha-brass) and optimize the c/a ratio for the hexagonal Zn-rich alloys for both the epsilon and eta phases.
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Affiliation(s)
- L Vitos
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044 Stockholm, Sweden
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81
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Nguyen-Manh D, Pettifor DG, Vitek V. Analytic environment-dependent tight-binding bond integrals: application to MoSi2. PHYSICAL REVIEW LETTERS 2000; 85:4136-4139. [PMID: 11056643 DOI: 10.1103/physrevlett.85.4136] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2000] [Indexed: 05/23/2023]
Abstract
We present the first derivation of explicit analytic expressions for the environmental dependence of the sigma, pi, and delta bond integrals within the orthogonal two-center tight-binding approximation by using the recently developed bond-order potential theory to invert the nonorthogonality matrix. We illustrate the power of this new formalism by showing that it not only captures the transferability of the bond integrals between elemental bcc Mo and Si and binary C11(b) MoSi2 but also predicts the absence of any discontinuity between first and second nearest neighbors for the ddsigma bond integral even though large discontinuities exist for ppsigma, pppi, and ddpi.
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Affiliation(s)
- D Nguyen-Manh
- Department of Materials, University of Oxford, Oxford, Parks Road, OX1 3PH, United Kingdom
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82
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Halley J, Schelling P, Duan Y. Simulation methods for chemically specific modeling of electrochemical interfaces. Electrochim Acta 2000. [DOI: 10.1016/s0013-4686(00)00578-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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83
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Boettger J, Trickey S. Inclusion of relativistic effects in Gaussian-basis density functional calculations for extended systems. ACTA ACUST UNITED AC 2000. [DOI: 10.1016/s0166-1280(99)00440-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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84
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85
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Affiliation(s)
- Akito Taneda
- Institute for Materials Research, Tohoku University
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