Dielectric Properties of Semiconductors by TDDFT in Real-Space and Real-Time Approach

2004 ◽  
Vol 829 ◽  
Author(s):  
Yasunari Zempo ◽  
Nobuhiko Akino
Keyword(s):  
Real Time ◽  
Density Functional ◽  
Real Space ◽  
Dielectric Constants ◽  
Functional Theory ◽  
The Real ◽  
Function Change ◽  
Experimental Values ◽  
Static Dielectric Constants ◽  
Band Separation

ABSTRACTThe dielectric responses of semiconductors such as C, Ge, Si, and AlGaAs are studied by the time-dependent density-functional theory. In our study, the real-space grid representation of the electron wave functions is used and the real-time approach is employed for the dynamics of the system. Both the static and dynamic dielectric functions are calculated, and we yielded that the static dielectric constants ε(0) are especially in good agreement with the experimental values. The effect of Al-component in the compound semiconductor AlxGa1−xAs is also studied. The peaks of the imaginary part of the dielectric function change with the band separation as a function of the Al-component. Furthermore, the static dielectric constants show the expected change due to the band separation as a function of the Al-component.

Optical Responses of Conjugated Polymers by TDDFT in Real-Space and Real-Time Approach

2004 ◽  
Vol 846 ◽  
Author(s):  
Nobuhiko Akino ◽  
Yasunari Zempo
Keyword(s):  
Conjugated Polymers ◽  
Real Time ◽  
Density Functional ◽  
Real Space ◽  
Time Dependent ◽  
Basis Set ◽  
Functional Theory ◽  
The Real ◽  
Optical Responses ◽  
Dependent Density

ABSTRACTThe time dependent density functional theory (TDDFT) has applied to study the optical responses of the conjugated polymers such as poly(p-phenylenevinylene) and poly(9, 9-dialkyl-fluorene). In our study, the real-space grid representation is used for the electron wavefunctions in contrast to a conventional basis set on each atom. In the calculations of the optical responses, the real-time approach is employed, where we follow the linear responses of the systems under externally applied perturbations in the real time. Since a real polymer is too large to handle, we have calculated the oligomers with different length and observed the spectrum peak is redshifted as the length of oligomer increases. The property of the polymer is extrapolated as the infinitely long oligomer. The estimated polymer spectra agree with the experiments reasonably well.

REAL-TIME APPROACH TO TIME-DEPENDENT DENSITY-FUNCTIONAL THEORY IN THE LINEAR AND NONLINEAR REGIME

2009 ◽  
Vol 08 (04) ◽  
pp. 561-574 ◽  
Author(s):  
MICHAEL MUNDT
Keyword(s):  
Density Functional Theory ◽  
Real Time ◽  
Density Functional ◽  
High Harmonic ◽  
External Perturbation ◽  
Real Space ◽  
Time Dependent ◽  
Functional Theory ◽  
Linear And Nonlinear ◽  
Dependent Density

The linear and nonlinear response of Si 4 and Na 4 to an external perturbation is investigated in the framework of time-dependent density-functional theory. The time-dependent Kohn–Sham equations, which are the central equations in this approach, are solved in real space and real time. A parallelized implementation to solve these nonlinear, one-particle Schrödinger equations is presented. In contrast to Na 4, Si 4 shows high-harmonic generation far beyond the cut-off predicted by the quasiclassical model and predictions for extended systems.

A UNION OF THE REAL-SPACE AND RECIPROCAL-SPACE VIEW OF THE GaAs(001) SURFACE

2001 ◽  
Vol 15 (17) ◽  
pp. 2301-2333 ◽  
Author(s):  
V. P. LaBELLA ◽  
Z. DING ◽  
D. W. BULLOCK ◽  
C. EMERY ◽  
P. M. THIBADO
Keyword(s):  
Density Functional ◽  
Lattice Gas ◽  
Real Space ◽  
Reciprocal Space ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Functional Theory ◽  
The Real ◽  
Reconstructed Surface ◽  
Temperature Measurement System

A union of the real-space and reciprocal space view of the GaAs(001) surface is presented. An optical transmission temperature measurement system allowed fast and accurate temperature determinations of the GaAs(001) substrate. The atomic features of the Ga A s (001)-(2×4) reconstructed surface are resolved with scanning tunneling microscopy and first principles density functional theory. In addition, the 2D lattice-gas Ising model within the grand canonical ensemble can be applied to this surface to understand the thermodynamics. An algorithm for using electron diffraction on the GaAs(001) surface to determine the substrate temperature and tune the nanoscale surface roughness is presented.

Properties of Cmc21-X2As2O (X = Si, Ge, and Sn) by First-Principles Calculations

2018 ◽  
Vol 73 (11) ◽  
pp. 1025-1035 ◽  
Author(s):  
Ruike Yang ◽  
Yucan Ma ◽  
Qun Wei ◽  
Dongyun Zhang
Keyword(s):  
Density Functional ◽  
Phonon Dispersion ◽  
Dielectric Constants ◽  
First Principles Calculations ◽  
Hybrid Functional ◽  
Functional Theory ◽  
Narrow Bandgap ◽  
Bandgap Semiconductors ◽  
Mechanical Strengths ◽  
Static Dielectric Constants

AbstractFor the compounds Cmc21-X2As2O (X = Si, Ge, and Sn), the stabilities are verified by the elastic constants and the phonon dispersion spectra. The structural, mechanical, electronic, and optical properties are investigated by using density functional theory (DFT) calculations. For Cmc21-X2As2O, the mechanical strengths in the [100], [010], and [001] directions are studied. Young’s modulus for Cmc21-Ge2As2O is more anisotropic than that of Cmc21-Si2As2O and Cmc21-Sn2As2O. The band structures of Cmc21-Si2As2O and Cmc21-Sn2As2O show that they are indirect-bandgap semiconductors with bandgaps of 2.744 and 2.201 eV, by using the HSE06 hybrid functional. Cmc21-Ge2As2O is a direct narrow-bandgap semiconductor with a bandgap of 2.131 eV. The static dielectric constants of Cmc21-Si2As2O and Cmc21-Sn2As2O in the [001] direction are higher than those in the [100] and [010] directions. The static dielectric constant of Cmc21-Ge2As2O in the [001] direction is lower than those in the [100] and [010] directions.

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