2,466 research outputs found
Advanced density matrix renormalization group method for nuclear structure calculations
We present an efficient implementation of the Density Matrix Renormalization
Group (DMRG) algorithm that includes an optimal ordering of the proton and
neutron orbitals and an efficient expansion of the active space utilizing
various concepts of quantum information theory. We first show how this new DMRG
methodology could solve a previous KeV discrepancy in the ground state
energy of Ni. We then report the first DMRG results in the
shell model space for the ground and first states of Ge
which are benchmarked with reference data obtained from Monte Carlo shell
model. The corresponding correlation structure among the proton and neutron
orbitals is determined in terms of the two-orbital mutual information. Based on
such correlation graphs we propose several further algorithmic improvement
possibilities that can be utilized in a new generation of tensor network based
algorithms.Comment: 5 pages, 4 figure
Determination of the absolute space directions between Baker-Nunn camera stations
Synthetic simultaneous observations for determining fixed-earth oriented directions between Baker-Nunn camera station
Principal spectra describing magnetooptic permittivity tensor in cubic crystals
We provide unified phenomenological description of magnetooptic effects being
linear and quadratic in magnetization. The description is based on few
principal spectra, describing elements of permittivity tensor up to the second
order in magnetization. Each permittivity tensor element for any magnetization
direction and any sample surface orientation is simply determined by weighted
summation of the principal spectra, where weights are given by crystallographic
and magnetization orientations. The number of principal spectra depends on the
symmetry of the crystal. In cubic crystals owning point symmetry we need only
four principal spectra. Here, the principal spectra are expressed by ab-initio
calculations for bcc Fe, fcc Co and fcc Ni in optical range as well as in hard
and soft x-ray energy range, i.e. at the 2p- and 3p-edges. We also express
principal spectra analytically using modified Kubo formula
H\"uckel--Hubbard-Ohno modeling of -bonds in ethene and ethyne with application to trans-polyacetylene
Quantum chemistry calculations provide the potential energy between two
carbon atoms in ethane (HCCH), ethene (HCCH), and ethyne
(HCCH) as a function of the atomic distance. Based on the energy
function for the -bond in ethane, , we use the H\"uckel
model with Hubbard--Ohno interaction for the ~electrons to describe the
energies and for the
double bond in ethene and the triple bond in ethyne,
respectively. The fit of the force functions shows that the Peierls coupling
can be estimated with some precision whereas the Hubbard-Ohno parameters are
insignificant at the distances under consideration. We apply the
H\"uckel-Hubbard-Ohno model to describe the bond lengths and the energies of
elementary electronic excitations of trans-polyacetylene, (CH), and adjust
the -bond potential for conjugated polymers.Comment: 10 pages, 7 figures, 3 table
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