252 research outputs found
Efficient and Accurate Linear Algebraic Methods for Large-scale Electronic Structure Calculations with Non-orthogonal Atomic Orbitals
The need for large-scale electronic structure calculations arises recently in
the field of material physics and efficient and accurate algebraic methods for
large simultaneous linear equations become greatly important. We investigate
the generalized shifted conjugate orthogonal conjugate gradient method, the
generalized Lanczos method and the generalized Arnoldi method. They are the
solver methods of large simultaneous linear equations of one-electron
Schr\"odinger equation and maps the whole Hilbert space to a small subspace
called the Krylov subspace. These methods are applied to systems of fcc Au with
the NRL tight-binding Hamiltonian (Phys. Rev. B {\bf 63}, 195101 (2001)). We
compare results by these methods and the exact calculation and show them
equally accurate. The system size dependence of the CPU time is also discussed.
The generalized Lanczos method and the generalized Arnoldi method are the most
suitable for the large-scale molecular dynamics simulations from the view point
of CPU time and memory size.Comment: 13pages, 7figure
Specific antigen of tumor cell transformed by DNA extracted from SV-40 virus
In the immunofluorescent study it has been revealed that rabbit sera immunized with transformed cells induced by SV-40 DNA, produce circulating antibody capable of re:lcting with intranuclear antigens synthesized by SV-40 complyte virus transforming process, In addition, the result confirmed that SV-40 DNA replicates DNA-containing
viruses in the host cell and that also the genome coding for the synthesis of SV-40 tumor antigen is resposible for viral DNA.</p
Linear Algebraic Calculation of Green's function for Large-Scale Electronic Structure Theory
A linear algebraic method named the shifted
conjugate-orthogonal-conjugate-gradient method is introduced for large-scale
electronic structure calculation. The method gives an iterative solver
algorithm of the Green's function and the density matrix without calculating
eigenstates.The problem is reduced to independent linear equations at many
energy points and the calculation is actually carried out only for a single
energy point. The method is robust against the round-off error and the
calculation can reach the machine accuracy. With the observation of residual
vectors, the accuracy can be controlled, microscopically, independently for
each element of the Green's function, and dynamically, at each step in
dynamical simulations. The method is applied to both semiconductor and metal.Comment: 10 pages, 9 figures. To appear in Phys. Rev. B. A PDF file with
better graphics is available at http://fujimac.t.u-tokyo.ac.jp/lses
An order-N electronic structure theory with generalized eigenvalue equations and its application to a ten-million-atom system
A linear-algebraic theory called 'multiple Arnoldi method' is presented and
realizes large-scale (order-N) electronic structure calculation with
generalized eigen-value equations. A set of linear equations, in the form of
(zS-H) x = b, are solved simultaneously with multiple Krylov subspaces. The
method is implemented in a simulation package ELSES (http://www.elses.jp) with
tight-binding-form Hamiltonians. A finite-temperature molecular dynamics
simulation is carried out for metallic and insulating materials. A calculation
with atoms was realized by a workstation. The parallel efficiency is
shown upto 1,024 CPU cores.Comment: 9 pages, 3 figures. To appear in J. Phys.: Condens. Matte
Theoretical analysis of GaAs/AlGaAs quantum dots in quantum wire array for intermediate band solar cell
A GaAs quantum dot (QD) array embedded in a AlGaAs host material was
fabricated using a strain-free approach, through combination of neutral beam etching
and atomic hydrogen-assisted molecular beam epitaxy regrowth. In this work, we
performed theoretical simulations on a GaAs/AlGaAs quantum well, GaAs QD and
QD array based intermediated band solar cell (IBSC) using a combined multiband
k·p and drift-diffusion transportation method. The electronic structure, IB band
dispersion, and optical transitions, including absorption and spontaneous emission
among the valence band, intermediate band, and conduction band, were calculated.
Based on these results, maximum conversion efficiency of GaAs/AlGaAs QD
array based IBSC devices were calculated by a drift-diffusion model adapted to
IBSC under the radiative recombination limit
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