26 research outputs found
Progress in Time-Dependent Density-Functional Theory
The classic density-functional theory (DFT) formalism introduced by
Hohenberg, Kohn, and Sham in the mid-1960s, is based upon the idea that the
complicated N-electron wavefunction can be replaced with the mathematically
simpler 1-electron charge density in electronic struc- ture calculations of the
ground stationary state. As such, ordinary DFT is neither able to treat
time-dependent (TD) problems nor describe excited electronic states. In 1984,
Runge and Gross proved a theorem making TD-DFT formally exact. Information
about electronic excited states may be obtained from this theory through the
linear response (LR) theory formalism. Begin- ning in the mid-1990s, LR-TD-DFT
became increasingly popular for calculating absorption and other spectra of
medium- and large-sized molecules. Its ease of use and relatively good accuracy
has now brought LR-TD-DFT to the forefront for this type of application. As the
number and the diversity of applications of TD-DFT has grown, so too has grown
our understanding of the strengths and weaknesses of the approximate
functionals commonly used for TD-DFT. The objective of this article is to
continue where a previous review of TD-DFT in this series [Annu. Rev. Phys.
Chem. 55: 427 (2004)] left off and highlight some of the problems and solutions
from the point of view of applied physical chemistry. Since doubly-excited
states have a particularly important role to play in bond dissociation and
formation in both thermal and photochemistry, particular emphasis will be
placed upon the problem of going beyond or around the TD-DFT adiabatic
approximation which limits TD-DFT calculations to nominally singly-excited
states. Posted with permission from the Annual Review of Physical Chemistry,
Volume 63 \c{opyright} 2012 by Annual Reviews, http://www.annualreviews.org
Application of time-dependent density functional theory to optical activity
As part of a general study of the time-dependent local density approximation
(TDLDA), we here report calculations of optical activity of chiral molecules.
The theory automatically satisfies sum rules and the Kramers-Kronig relation
between circular dichroism and optical rotatory power. We find that the theory
describes the measured circular dichroism of the lowest states in methyloxirane
with an accuracy of about a factor of two. In the chiral fullerene C_76 the
TDLDA provides a consistent description of the optical absorption spectrum, the
circular dichroism spectrum, and the optical rotatory power, except for an
overall shift of the theoretical spectrum.Comment: 17 pages and 13 PostScript figure
Melting a Hubbard dimer: benchmarks of 'ALDA' for quantum thermodynamics
The competition between evolution time, interaction strength, and temperature
challenges our understanding of many-body quantum systems out-of-equilibrium.
Here we consider a benchmark system, the Hubbard dimer, which allows us to
explore all the relevant regimes and calculate exactly the related average
quantum work. At difference with previous studies, we focus on the effect of
increasing temperature, and show how this can turn competition between
many-body interactions and driving field into synergy. We then turn to use
recently proposed protocols inspired by density functional theory to explore if
these effects could be reproduced by using simple approximations. We find that,
up to and including intermediate temperatures, a method which borrows from
ground-state adiabatic local density approximation improves dramatically the
estimate for the average quantum work, including, in the adiabatic regime, when
correlations are strong. However at high temperature and at least when based on
the pseudo-LDA, this method fails to capture the counterintuitive qualitative
dependence of the quantum work with interaction strength, albeit getting the
quantitative estimates relatively close to the exact results
Regarding the use and misuse of retinal protonated Schiff base photochemistry as a test case for time-dependent density-functional theory
The excited-state relaxation of retinal protonated Schiff bases (PSBs) is an important test case for biological applications of time-dependent (TD) density-functional theory (DFT). While well-known shortcomings of approximate TD-DFT might seem discouraging for application to PSB relaxation, progress continues to be made in the development of new functionals and of criteria allowing problematic excitations to be identified within the framework of TD-DFT itself. Furthermore, experimental and theoretical ab initio advances have recently lead to a revised understanding of retinal PSB photochemistry, calling for a reappraisal of the performance of TD-DFT in describing this prototypical photoactive system. Here, we re-investigate the performance of functionals in (TD-)DFT calculations in light of these new benchmark results, which we extend to larger PSB models. We focus on the ability of the functionals to describe primarily the early skeletal relaxation of the chromophore and investigate how far along the out-of-plane pathways these functionals are able to describe the subsequent rotation around formal single and double bonds. Conventional global hybrid and range-separated hybrid functionals are investigated as the presence of Hartree-Fock exchange reduces problems with charge-transfer excitations as determined by the Peach-Benfield-Helgaker-Tozer Λ criterion and by comparison with multi-reference perturbation theory results. While we confirm that most functionals cannot render the complex photobehavior of the retinal PSB, do we also observe that LC-BLYP gives the best description of the initial part of the photoreaction