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An efficient first-principle approach for electronic structures calculations of nanomaterials
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
Chinese Acad Sci, Inst High Energy Phys, Beijing.
Show others and affiliations
2008 (English)In: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 29, no 3, 434-444 p.Article in journal (Refereed) Published
Abstract [en]

An efficient parallel implementation has been realized for a recently proposed central insertion scheme (Jiang, Liu, Lu, Luo. J Chem Phys 2006,124,214711; J Chem Phys 2006,125, 149902) that allows to calculate electronic structures of nanomaterials at various density functional theory levels. It has adopted the sparse-matrix format for Fock/Kohn-Sham and overlap matrices, as well as a combination of implicitly restarted Arnoldi methods (IRAM) and spectral transformation for computing selected eigenvalues/eigenvectors. A systematic error analysis and control for the proposed method has been provided based on a strict mathematical basis. The efficiency and applicability of the new implementation have been demonstrated by calculations of electronic structures of two different nanomaterials consisting of one hundred thousand electrons.

Place, publisher, year, edition, pages
2008. Vol. 29, no 3, 434-444 p.
Keyword [en]
nanomaterials; density functional theory; electronic structures; carbon nanotubes; diamondoids
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6984DOI: 10.1002/jcc.20799ISI: 000252864500011Scopus ID: 2-s2.0-38349153574OAI: oai:DiVA.org:kth-6984DiVA: diva2:11851
Note
QC 20100726Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-07-30Bibliographically approved
In thesis
1. Theoretical Characterization of Optical Processes in Modecular Complexes
Open this publication in new window or tab >>Theoretical Characterization of Optical Processes in Modecular Complexes
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The main theme of this thesis is to study effects of different environments on geometric and electronic structures, as well as optical responses, of molecules using time-(in)dependent density functional theory. Theoretical calculations have been carried out for properties that can be measured by conventional and advanced experimental techniques, including one-photon absorption (OPA), two-photon absorption (TPA), surface-enhanced Raman scattering (SERS) and second order nonlinear optical (NLO) response. The obtained good agreement between the theory and the experiment allows to further extract useful information about inter- and intra-molecular interactions that are not accessible experimentally.

By comparing calculated one-photon absorption spectra of aluminum phthalocyanine chloride (AlPcCl) and AlPcCl -water complexes with the corresponding experiments, detailed information about the interaction between water molecules and AlPcCl, and geometric changes of AlPcCl molecule has been obtained. Effects of aggregation on two-photon absorption spectra of octupolar molecules have been examined. It is shown that the formation of clusters through inter-molecular hydrogen bonding can drastically change profiles of TPA spectra. It has also demonstrated that a well designed molecular aggregate/cluster, dendrimer, can enhance the second order nonlinear optical response of the molecules. In collaboration with experimentalists, a series of end-capped triply branched dendritic chromophores have been characterized, which can lead to large enhancement of the second order NLO property when the dipoles of the three branches in the dendrimers are highly parallelized.

Surface-enhanced Raman scattering has made the detection of single molecules on metal surface become possible. Chemically bonded molecule-metal systems have been extensively studied. We have shown in a joint experimental and theoretical work that stable Raman spectra of a non-bonding molecule, perylene, physically adsorbed on Ag nano-particles can also be observed at low temperature. It is found that the local enhanced field has a tendency to drive molecule toward a gap of two closely lying nano-particles. The trapped molecule can thus provide a stable Raman spectrum with high resolution when its thermal motion is reduced at low temperature.

For the ever growing size of molecular complexes, there is always the need to develop new computational methods. A conceptually simple but computationally efficient method, named as central insertion scheme (CIS), is proposed that allows to calculate electronic structure of quasi-periodic system containing more than 100,000 electrons at density functional theory levels. It enables to monitor the evolution of electronic structure with respect to the size of the system.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 60 p.
Keyword
one-photon absorption, two-photon absorption, surface-enhanced Raman scattering
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-4629 (URN)978-91-7178-857-3 (ISBN)
Public defence
2008-02-25, FA32, Roslagstullsbacken 21, AlbaNova University Center, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100823Available from: 2008-02-05 Created: 2008-02-05 Last updated: 2010-08-23Bibliographically approved
2. First Principles Studies of Carbon Based Molecular Materials
Open this publication in new window or tab >>First Principles Studies of Carbon Based Molecular Materials
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to investigate carbon based molecular materials at first principles levels. Special attention has been paid to simulations of X-ray spectroscopies, including near edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron, and X-ray emission spectroscopy, which can provide detailed information about core, occupied and unoccupied molecular orbitals of the systems under investigation. Theoretical calculations have helped to assign fine spectral structures in high resolution NEXAFS spectra of five azabenzenes (pyridine, pyrazine, pyrimidine, pyridazine and s-triazine), and to identify different local chemical environments among them. With the help of NEXAFS, the characters of important chemical bonds that might be responsible for the unique magnetic properties of the tetracyanoethylene compound has been revealed. Calculations have demonstrated that X-ray spectroscopies are powerful tools for isomer identification and structure determination of fullerenes and endohedral metallofullerenes. A joint experimental and theoretical study on metallofullerene Gd@C82 has firmly determined its equilibrium structure, in which the gadolinium atom lies above the hexagon on the C2 axis. It is found that the gadolinium atom could oscillate around its equilibrium position and that its oscillation amplitude increases with increasing temperature.

In this thesis, several new computational schemes for large-scale systems have been proposed. Parallel implementation of a central insertion scheme (CIS) has been realized, which allows to effectively calculate electronic structures of very large systems, up to 150,000 electrons, at hybrid density functional theory levels. In comparison with traditional computational methods, CIS provides results with the same high accuracy but requires only a fraction of computational time. One of its applications is to calculate electronic structures of nanodiamond clusters varying from 0.76 nm (29 carbons) to 7.3 nm (20,959 carbons) in diameter, which enabled to resolve the long-standing debate about the validity of the quantum confinement model for nanodiamonds. Electronic structures and X-ray spectroscopies of a series of single-walled carbon nanotubes (SWCNTs) with different diameters and lengths have been calculated, which have made it possible to interpret the existing experimental results.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. x, 63 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2008:10
Keyword
first principles simulations, carbon based molecular materials, X-ray spectroscopies
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-4724 (URN)978-91-7178-963-1 (ISBN)
Public defence
2008-05-23, FB42, AlbaNova, Roslagstullsbaken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100727Available from: 2008-05-06 Created: 2008-05-06 Last updated: 2010-07-27Bibliographically approved
3. A Quantum Chemical View of Molecular and Nano-Electronics
Open this publication in new window or tab >>A Quantum Chemical View of Molecular and Nano-Electronics
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This dissertation presents a generalized quantum chemical approach for electron transport in molecular electronic devices based on Green's function scattering theory. It allows to describe both elastic and inelastic electron transport processes at first principles levels of theory, and to treat devices with metal electrodes either chemically or physically bonded to the molecules on equal footing. Special attention has been paid to understand the molecular length dependence of current-voltage characteristics of molecular junctions. Effects of external electric fields have been taken into account non-perturbatively, allowing to treat electrochemical gate-controlled single molecular field effect transistors for the first time. Inelastic electron tunneling spectroscopy of molecular junctions has been simulated by including electron-vibration couplings. The calculated spectra are often in excellent agreement with experiment, revealing detailed structure information about the molecule and the bonding between molecule and metal electrodes that are not accessible in the experiment.

An effective central insertion scheme (CIS) has been introduced to study electronic structures of nanomaterials at first principles levels. It takes advantage of the partial periodicity of a system and uses the fact that long range interaction in a big system dies out quickly. CIS method can save significant computational time without loss of accuracy and has been successfully applied to calculate electronic structures of one- , two- , and three-dimensional nanomaterials, such as sub-116 nm long conjugated polymers, sub-200nm long single-walled carbon nanotubes, sub-60 base pairs DNA segments, nanodiamondoids of sub-7.3nm in diameter and Si-nanoparticles of sub-6.5nm in diameter at the hybrid density functional theory level. The largest system under investigation consists of 100,000 electrons. The formation of energy bands and quantum confinement effects in these nanostructures have been revealed. Electron transport properties of polymers, SWCNTs and DNA have also been calculated.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 70 p.
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-4335 (URN)978-91-7178-618-0 (ISBN)
Public defence
2007-04-24, FA32, AlbaNova, Roslagstullsbacken, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100729. Ändrat felaktig titel "Theoretical Chemistry, Molecular and Nano-electronics" 20100729.Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2010-07-30Bibliographically approved

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