5 research outputs found
Dynamical density-matrix renormalization-group method
I present a density-matrix renormalization-group (DMRG) method for
calculating dynamical properties and excited states in low-dimensional lattice
quantum many-body systems. The method is based on an exact variational
principle for dynamical correlation functions and the excited states
contributing to them. This dynamical DMRG is an alternate formulation of the
correction vector DMRG but is both simpler and more accurate. The finite-size
scaling of spectral functions is discussed and a method for analyzing the
scaling of dense spectra is described. The key idea of the method is a
size-dependent broadening of the spectrum.The dynamical DMRG and the
finite-size scaling analysis are demonstrated on the optical conductivity of
the one-dimensional Peierls-Hubbard model. Comparisons with analytical results
show that the spectral functions of infinite systems can be reproduced almost
exactly with these techniques. The optical conductivity of the Mott-Peierls
insulator is investigated and it is shown that its spectrum is qualitatively
different from the simple spectra observed in Peierls (band) insulators and
one-dimensional Mott-Hubbard insulators.Comment: 16 pages (REVTEX 4.0), 10 figures (in 13 EPS files
Reversible Pressure-Induced Amorphization in Solid C70 : Raman and Photoluminescence Study
We have studied single crystals of by Raman scattering and
photoluminescence in the pressure range from 0 to 31.1 GPa. The Raman spectrum
at 31.1 GPa shows only a broad band similar to that of the amorphous carbon
without any trace of the Raman lines of . After releasing the pressure
from 31.1 GPa, the Raman and the photoluminescence spectra of the recovered
sample are that of the starting crystal. These results indicate that
the molecules are stable upto 31.1 GPa and the amorphous carbon high
pressure phase is reversible, in sharp contrast to the results on solid
. A qualitative explaination is suggested in terms of inter- versus
intra-molecular interactions.Comment: To appear in Phys. Rev. Lett., 12 pages, RevTeX (preprint format), 3
figures available upon reques