Browsing by Author "Irle, Stephan"

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Automatized Parameterization of DFTB Using Particle Swarm Optimization
(2016-01)
Chou, Chien-Pin
;
Nishimura, Yoshifumi
;
Fan, Chin-Chai
;
Mazur, Grzegorz
;
Irle, Stephan
We present a novel density-functional tight-binding (DFTB) parametrization toolkit developed to optimize the parameters of various DFTB models in a fully automatized fashion. The main features of the algorithm, based on the particle swarm optimization technique, are discussed, and a number of initial pilot applications of the developed methodology to molecular and solid systems are presented.
Automatized Parameterization of DFTB Using Particle Swarm Optimization
(2016-01-01)
Chou, Chien-Pin
;
Nishimura, Yoshifumi
;
Fan, Chin-Chai
;
Mazur, Grzegorz
;
Irle, Stephan
We present a novel density-functional tight-binding (DFTB) parametrization toolkit developed to optimize the parameters of various DFTB models in a fully automatized fashion. The main features of the algorithm, based on the particle swarm optimization technique, are discussed, and a number of initial pilot applications of the developed methodology to molecular and solid systems are presented.
Automatized Parameterization of the Density-functional Tight-binding Method. II. Two-center Integrals
(2016-01-01)
Witek, Henryk A.
;
Chou, Chien-Pin
;
Mazur, Grzegorz
;
Nishimura, Yoshifumi
;
Irle, Stephan
We present an efficient numerical integration scheme (TWOCENT) to be used in the context of automatized parameterization of the density-functional tight-binding (DFTB) method. The accuracy of the integration process is assessed and its range of applicability is discussed. The functionality of the developed code is tested by reproducing the electronic portion of the existing mio parameter sets and by reproducing a series of reference DFT band structures of elemental solids.
Automatized Parameterization of the Density-functional Tight-binding Method. II. Two-center Integrals
(2016-01)
Witek, Henryk A.
;
Chou, Chien-Pin
;
Mazur, Grzegorz
;
Nishimura, Yoshifumi
;
Irle, Stephan
We present an efficient numerical integration scheme (TWOCENT) to be used in the context of automatized parameterization of the density-functional tight-binding (DFTB) method. The accuracy of the integration process is assessed and its range of applicability is discussed. The functionality of the developed code is tested by reproducing the electronic portion of the existing mio parameter sets and by reproducing a series of reference DFT band structures of elemental solids.
COMP 105-Prediction of Raman spectra in novel polyyne@SWNT peapods using dispersion-augmented density-functional-tight-binding
(2007-08-19)
Irle, Stephan
;
Witek, Henryk A.
;
Shinohara, Hisanori
;
Morokuma, Keiji
;
應用化學系
Comparison of Geometric, Electronic, and Vibrational Properties for All Pentagon/Hexagon-Bearing Isomers of Fullerenes C(38), C(40), and C(42)
(2009-08-05)
Malolepsza, Edyta
;
Lee, Yuan-Pern
;
Witek, Henryk A.
;
Irle, Stephan
;
Lin, Chun-Fu
The self-consistent-charge density-functional tight-binding (SCC-DFTB) method is employed for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all pentagon/hexagon-bearing isomers of C(38), C(40), and C(42) as the second part of a larger effort to catalogue the CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C(20)-C(180) [analogous data for C(20)-C(36) were published previously in Malolepsza et al., J Phys Chem A, 2007, 111, 6649]. Common features among the fullerenes are identified and properties characteristic for each specific fullerene cage size are discussed. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1999-2011, 2009
Comparison of Geometric, Electronic, and Vibrational Properties for All Pentagon/Hexagon-Bearing Isomers of Fullerenes C-38, C-40, and C-42
(2009-08-05)
Malolepsza, Edyta
;
Lee, Yuan-Pern
;
Witek, Henryk A.
;
Irle, Stephan
;
Lin, Chun-Fu
The self-consistent-charge density-functional tight-binding (SCC-DFTB) method is employed for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all pentagon/hexagon-bearing isomers of C-38, C-40, and C-42 as the second part of a larger effort to catalogue the CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C-20-C-180 [analogous data for C-20-C-36 were published previously in Malolepsza et al., J Phys Chem A, 2007, 111, 6649]. Common features among the fullerenes are identified and properties characteristic for each specific fullerene cage size are discussed. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1999-2011, 2009
Comparison of geometric, electronic, and vibrational properties for isomers of small fullerenes C-20-C-36
(2007-07-26)
Malolepsza, Edyta
;
Witek, Henryk A.
;
Irle, Stephan
;
應用化學系
;
應用化學系分子科學碩博班
We employ the self-consistent-charge density-functional tight-binding (SCC-DFTB) method for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all 35 five- and six-member rings containing isomers of small fullerenes, C-20, C-24, C-26, C-28, C-30, C-32, C-34, and C-36, as first part of a larger effort to catalog CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C-20-C-180. Common features among the fullerenes are identified and properties characteristic for each specific fullerene isomer are discussed.
Convergence in the Evolution of Nanodiamond Raman Spectra with Particle Size: A Theoretical Investigation
(2010-08-01)
Li, Wunfan
;
Irle, Stephan
;
Witek, Henryk A.
;
應用化學系
;
應用化學系分子科學碩博班
Structural characterization of nanodiamonds by vibrational spectroscopy requires knowledge of the factors determining the spectra. Raman spectroscopy is widely used to detect the diamond phase in nanodiamond powders and films, but several spectral features are still poorly understood. Here we present a theoretical study of the evolution of diamond hydrocarbon Raman spectra with increasing size, from the adamantane molecule to similar to 3 nm large tetrahedral and octahedral particles of T(d) symmetry, containing up to about 1000 carbon atoms. The self-consistent-charge density functional tight-binding method (SCC-DFTB) was used for the calculation of harmonic first-order Raman spectra. We demonstrate very good agreement with Raman spectra computed by standard density functional theory (DFT) for the smaller model systems. The evolution of the Raman patterns is smooth, and convergence to the bulk limit could clearly be observed in case of the acoustic vibrational modes (omega(A) = 0 cm(-1)). We found a simple relationship between nanodiamond size and vibrational frequency, which is analogous to the corresponding equation for the radial breathing mode of single-walled carbon nanotubes. The T(2) modes of octahedral diamond hydrocarbons coalesce faster to the bulk optical vibrational mode (in experiment, omega(0) = 1332 cm(-1)) than those of tetrahedral particles, consistent with the fact that the bulk/surface ratio is more favorable for octahedral particles. Our simulations unequivocally show that controversial Raman features around 500 and 1150 cm(-1) do not originate from the nanodiamond crystals, and that the nanocrystal shape plays an important role in the appearance of the Raman spectra even in the 3 nm domain.
Critical interpretation of CH- and OH- stretching regions for infrared spectra of methanol clusters (CH3OH)(n) (n=2-5) using self-consistent-charge density functional tight-binding molecular dynamics simulations
(2014-09-07)
Nishimura, Yoshifumi
;
Lee, Yuan-Pern
;
Irle, Stephan
;
Witek, Henryk A.
;
交大名義發表
Vibrational infrared (IR) spectra of gas-phase O-H center dot center dot center dot O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that nu(3), nu(9), and nu(2) C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum. (C) 2014 AIP Publishing LLC.
Diversity in electronic structure and vibrational properties of fullerene isomers correlates with cage curvature
(2016-04)
Witek, Henryk A.
;
Irle, Stephan
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
A theoretical study of pentagon/hexagon-bearing isomers of the C-32 and C-86 fullerenes suggests that the diversity in electronic structure and vibrational properties is determined by the surface curvature of the fullerene cage rather than by the global bond network topology. The latter plays a greater role in small, highly constrained fullerene cages, while it can be safely ignored in the case of larger isomers. Selection rules of infrared and Raman spectroscopy are the origin for exceptions from this pattern for bond topologies corresponding to high point-group symmetries of the fullerene cage. The presented data conforms to the common knowledge that discriminating between various isomers of larger fullerenes can constitute a difficult experimental task. (C) 2016 Elsevier Ltd. All rights reserved.
Dramatic Reduction of IR Vibrational Cross Sections of Molecules Encapsulated in Carbon Nanotubes
(2011-06-01)
Kazachkin, Dmitry V.
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Nishimura, Yoshifumi
;
Witek, Henryk A.
;
Irle, Stephan
;
Borguet, Eric
Combined temperature-programmed desorption and IR studies suggest that absorption cross sections of IR-active vibrations of molecules "strongly" bound to single-wall sidewalls as the origin of such "screening". The observed and identify dielectric screening by highly polarizable SWCNT endohedrally encapsulated molecules are dramatically reduced, carbon nanotubes (SWCNTs) are reduced at least by a factor of 10. Quantum chemical simulations show that IR intensities of intensity reduction originates from a sizable cancellation of adsorbate dipole moments by mirror charges dynamically induced on the nanotube sidewalls. For exohedrally adsorbed molecules, the dielectric screening is found to be orientation-dependent with a smaller magnitude for adsorption in groove and interstitial sites. The presented results clearly demonstrate and quantify the screening effect of SWCNTs and unequivocally show that IR spectroscopy cannot be applied in a straightforward manner to the study of peapod systems.
Modeling carbon nanostructures with the self-consistent charge density-functional tight-binding method: Vibrational spectra and electronic structure of C-28, C-60, and C-70
(2006-12-07)
Witek, Henryk A.
;
Irle, Stephan
;
Zheng, Guishan
;
de Jong, Wibe A.
;
Morokuma, Keiji
The self-consistent charge density-functional tight-binding (SCC-DFTB) method is employed for studying various molecular properties of small fullerenes: C-28, C-60, and C-70. The computed bond distances, vibrational infrared and Raman spectra, vibrational densities of states, and electronic densities of states are compared with experiment (where available) and density-functional theory (DFT) calculations using various basis sets. The presented DFT benchmark calculations using the correlation-consistent polarized valence triple zeta basis set are at present the most extensive calculations on harmonic frequencies of these species. Possible limitations of the SCC-DFTB method for the prediction of molecular vibrational and optical properties are discussed. The presented results suggest that SCC-DFTB is a computationally feasible and reliable method for predicting vibrational and electronic properties of such carbon nanostructures comparable in accuracy with small to medium size basis set DFT calculations at the computational cost of standard semiempirical methods. (c) 2006 American Institute of Physics.
Quantum chemical investigation of epoxide and ether groups in graphene oxide and their vibrational spectra
(2013)
Page, Alister J.
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Chou, Chien-Pin
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Pham, Buu Q.
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Witek, Henryk A.
;
Irle, Stephan
We present a detailed analysis of the factors influencing the formation of epoxide and ether groups in graphene nanoflakes using conventional density functional theory (DFT), the density-functional tight-binding (DFTB) method, pi-Huckel theory, and graph theoretical invariants. The relative thermodynamic stability associated with the chemisorption of oxygen atoms at various positions on hexagonal graphene flakes (HGFs) of D-6h-symmetry is determined by two factors - viz. the disruption of the p-conjugation of the HGF and the geometrical deformation of the HGF structure. The thermodynamically most stable structure is achieved when the former factor is minimized, and the latter factor is simultaneously maximized. Infrared (IR) spectra computed using DFT and DFTB reveal a close correlation between the relative thermodynamic stabilities of the oxidized HGF structures and their IR spectral activities. The most stable oxidized structures exhibit significant IR activity between 600 and 1800 cm(-1), whereas less stable oxidized structures exhibit little to no activity in this region. In contrast, Raman spectra are found to be less informative in this respect.
Theoretical study of cellobiose hydrolysis to glucose in ionic liquids
(2014-05-30)
Nishimura, Yoshifumi
;
Yokogawa, Daisuke
;
Irle, Stephan
;
應用化學系
;
應用化學系分子科學碩博班
The S(N)1-type hydrolysis reaction of cellobiose in ionic liquids (ILs) was theoretically investigated. First principles and ab initio quantum chemical methods were used in conjunction with the \'reference interaction site model self-consistent field with spatial electron density distribution\' (RISM-SCF-SEDD) method. Reaction mechanism pathways are discussed and compared to calculations in gas phase and in aqueous solution. Analysis of solvation effects indicates strong interaction between hydrogen atoms of glucose hydroxyl groups and the anions in ILs, contributing to large stabilization of the reaction product. The calculated activation energy in ILs (24.5 kcal/mol) agrees quantitatively with the experimental value (26.5 kcal/mol). (C) 2014 Elsevier B. V. All rights reserved.
When finite becomes infinite: convergence properties of vibrational spectra of oligomer chains
(2018-10-01)
Chou, Chien-Pin
;
Witek, Henryk
;
Irle, Stephan
;
交大名義發表
;
應用化學系
We present a computational study of convergence properties of vibrational IR and Raman spectra for a series of increasingly long units of polyethylene, cis- and trans-polyacetylenes, and polyynes. Convergent behavior to the spectra of infinitely long polymers was observed in all cases when chains reached lengths of approximately 60 carbon atoms, both with respect to the positions of the bands and to their intensities. The vibrational spectra of longer chains are practically indistinguishable. The convergence rate depends on the degree of the conjugation in a studied system: Vibrational spectra for oligoethylenes converge noticeably faster than the spectra for the conjugated systems. The slowest convergence is observed for skeletal motions of the oligomer chains, which may require more than a hundred carbon atoms in the chain to show deviations smaller than 1cm(-1) to the corresponding solid-state calculations. The results suggest that the boundary between the properties of finite and infinite molecular systems fades away for a surprisingly small number of atoms.