Browsing by Author "Morokuma, Keiji"

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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
Computational study of molecular properties of aggregates of C-60 and (16,0) zigzag nanotube
(2007-09-26)
Witek, Henryk A.
;
Trzaskowski, Bartosz
;
Malolepza, Edyta
;
Morokuma, Keiji
;
Adamowicz, Ludwik
Molecular properties for two aggregates of C-60 and a (16, 0) zigzag nanotube: (a) C-60 encapsulated in the nanotube, (b) C-60 attached to the outer wall of the nanotube, are studied using the self-consistent charge density-functional tight-binding method with additional dispersion correction. The binding energy for the encapsulated fullerene is -108.3 kcal/mol and for the attached fullerene, only -20.3 kcal/mol. The harmonic vibrational frequencies of the aggregates are found to be almost identical to those obtained for the non-interacting system. Very small extent of the changes upon interaction may pose a challenge to study the aggregated structures using experimental spectroscopic methods. (C) 2007 Elsevier B.V. All rights reserved.
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.
;
Chou, Chien-Pin
;
Pham, Buu Q.
;
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.
Relativistic parametrization of the self-consistent-charge density-functional tight-binding method. 1. Atomic wave functions and energies
(2007-07-05)
Witek, Henryk A.
;
Koehler, Christof
;
Frauenheim, Thomas
;
Morokuma, Keiji
;
Elstner, Marcus
A detailed treatment of a confined relativistic atom, needed as an initial step for the parametrization of the self-consistent-charge density-functional tight-binding method, is presented and discussed. The required one-component quantities, i.e., orbital energies, orbital wave functions, and Hubbard parameters, are obtained by weighted averaging of the corresponding numbers determined for the atomic spinors. The wave function and density confinement is achieved by introducing the Woods-Saxon potential in the atomic four-component Dirac-Kohn-Sham problem. The effect of the additional confining potential on energy eigenvalues and the shape of atomic wave functions and densities is discussed and numerical examples are presented for the valence spinors of carbon, germanium, and lead.