28 research outputs found
Relativistic effects on the Fukui function
The extent of relativistic effects on the Fukui function, which describes local reactivity trends within conceptual density functional theory (DFT), and frontier orbital densities has been analysed on the basis of three benchmark molecules containing the heavy elements: Au, Pb, and Bi. Various approximate relativistic approaches have been tested and compared with the four-component fully relativistic reference. Scalar relativistic effects, as described by the scalar zeroth-order regular approximation methodology and effective core potential calculations, already provide a large part of the relativistic corrections. Inclusion of spin-orbit coupling effects improves the results, especially for the heavy p-block compounds. We thus expect that future conceptual DFT-based reactivity studies on heavy-element molecules can rely on one of the approximate relativistic methodologie
Complete-Graph Tensor Network States: A New Fermionic Wave Function Ansatz for Molecules
We present a new class of tensor network states that are specifically
designed to capture the electron correlation of a molecule of arbitrary
structure. In this ansatz, the electronic wave function is represented by a
Complete-Graph Tensor Network (CGTN) ansatz which implements an efficient
reduction of the number of variational parameters by breaking down the
complexity of the high-dimensional coefficient tensor of a
full-configuration-interaction (FCI) wave function. We demonstrate that CGTN
states approximate ground states of molecules accurately by comparison of the
CGTN and FCI expansion coefficients. The CGTN parametrization is not biased
towards any reference configuration in contrast to many standard quantum
chemical methods. This feature allows one to obtain accurate relative energies
between CGTN states which is central to molecular physics and chemistry. We
discuss the implications for quantum chemistry and focus on the spin-state
problem. Our CGTN approach is applied to the energy splitting of states of
different spin for methylene and the strongly correlated ozone molecule at a
transition state structure. The parameters of the tensor network ansatz are
variationally optimized by means of a parallel-tempering Monte Carlo algorithm
Spin in Density-Functional Theory
The accurate description of open-shell molecules, in particular of transition
metal complexes and clusters, is still an important challenge for quantum
chemistry. While density-functional theory (DFT) is widely applied in this
area, the sometimes severe limitations of its currently available approximate
realizations often preclude its application as a predictive theory. Here, we
review the foundations of DFT applied to open-shell systems, both within the
nonrelativistic and the relativistic framework. In particular, we provide an
in-depth discussion of the exact theory, with a focus on the role of the spin
density and possibilities for targeting specific spin states. It turns out that
different options exist for setting up Kohn-Sham DFT schemes for open-shell
systems, which imply different definitions of the exchange-correlation energy
functional and lead to different exact conditions on this functional. Finally,
we suggest some possible directions for future developments
Quantum bits with Josephson junctions
Already in the first edition of this book (Barone and Paterno, "Fundamentals
and Physics and Applications of the Josephson Effect", Wiley 1982), a great
number of interesting and important applications for Josephson junctions were
discussed. In the decades that have passed since then, several new applications
have emerged. This chapter treats one such new class of applications: quantum
optics and quantum information processing (QIP) based on superconducting
circuits with Josephson junctions. In this chapter, we aim to explain the
basics of superconducting quantum circuits with Josephson junctions and
demonstrate how these systems open up new prospects, both for QIP and for the
study of quantum optics and atomic physics.Comment: 30 pages, 10 figures. Book chapter for a new edition of Barone and
Paterno's "Fundamentals and Physics and Applications of the Josephson
Effect". Final versio
Relativistic effects on the Fukui function
ISSN:1432-881XISSN:1432-223
04441 Working Group - Some Open Aspects of Mobile Ad-hoc NETwork, Peer-to-Peer, and Self-organizing Systems
This document summarizes the results of the working group discussion on Mobile Ad-hoc NETworks (MANETs), peer-to-peer (p2p) and self-organizing systems held at the workshop on Mobile Information Management in October