scholarly journals KEY CONCEPTS IN TIME-DEPENDENT DENSITY-FUNCTIONAL THEORY

2001 ◽  
Vol 15 (14) ◽  
pp. 1969-2023 ◽  
Author(s):  
ROBERT VAN LEEUWEN
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Time Dependent ◽  
Response Functions ◽  
Many Body ◽  
Functional Theory ◽  
Key Concepts ◽  
Initial States ◽  
Many Body Systems ◽  
Dependent Density

We give an overview of the underlying concepts of time-dependent density-functional theory. The basic relations between densities, potentials and initial states, for time-dependent many-body systems are discussed. We obtain some new results concerning the invertability of response functions. Some fundamental difficulties associated with the time-dependent action principle are discussed and we show how these difficulties can be resolved by means of the Keldysh formalism.

EXCHANGE–CORRELATION KERNEL IN TIME-DEPENDENT DENSITY FUNCTIONAL THEORY DERIVED FROM MANY-BODY THEORY

2004 ◽  
Vol 18 (07) ◽  
pp. 1055-1067 ◽  
Author(s):  
K. KARLSSON ◽  
F. ARYASETIAWAN
Keyword(s):  
Density Functional Theory ◽  
Optical Absorption ◽  
Density Functional ◽  
Time Dependent ◽  
Many Body ◽  
Functional Theory ◽  
Correlation Kernel ◽  
Exchange Correlation ◽  
Many Body Theory ◽  
Dependent Density

We derive a simplified Bethe–Salpeter equation for calculating optical absorption based on the assumption of a local electron–hole interaction. The original four-point equation for the kernel is reduced to a two-point one. A connection to the exchange–correlation kernel in time-dependent density functional theory can be established. The resulting fxc is found to be -W/2 where W contains only the short-range (local) part of the Coulomb screened interaction. This simple approximation was successfully applied to optical absorption spectra of some excitonic crystals, reproducing not only the continuum excitons but also the bound ones.

Cubic response functions in time-dependent density functional theory

2005 ◽  
Vol 122 (5) ◽  
pp. 054107 ◽  
Author(s):  
Branislav Jansik ◽  
Paweł Sałek ◽  
Dan Jonsson ◽  
Olav Vahtras ◽  
Hans Ågren
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Time Dependent ◽  
Response Functions ◽  
Functional Theory ◽  
Dependent Density

scholarly journals A Natural Orbital Branching Scheme for Time Dependent Density Functional Theory Nonadiabatic Simulations

2020 ◽  
Author(s):  
Lin-Wang Wang
Keyword(s):  
Density Functional Theory ◽  
Wave Function ◽  
Density Functional ◽  
Detailed Balance ◽  
Time Dependent ◽  
Natural Orbital ◽  
Many Body ◽  
Functional Theory ◽  
Orbital Branching ◽  
Dependent Density

Real time time dependent density functional theory (rt-TDDFT) has now been used to study a wide range of problems, from optical excitation, to charge transfer, to ion collision, to ultrafast phase transition. However, conventional rt-TDDFT Ehrenfest dynamics for nuclear movement lacks a few critical features to describe many problems: the detail balance between state transition, decoherence for the wave function evolution, and stochastic branching of the nuclear trajectory. There are many-body formalisms to describe such nonadiabatic molecular dynamics, especially the ones based on mixed quantum/classical simulations, like the surface hopping and wave function collapsing schemes. However, there are still challenges to implement such many-body formalisms to the rt-TDDFT simulations, especially for large systems where the excited state electronic structure configuration space is large. Here we introduce two new algorithm for nonadiabatic rt-TDDFT simulations: the first is a Boltzmann factor algorithm which introduces decoherence and detailed balance in the carrier dynamics, but uses mean field theory for nuclear trajectory. The second is a natural orbital branching (NOB) formalism, which use time dependent density matrix for electron evolution, and natural orbital to collapse the wave function upon. It provides decoherence, detailed balance and trajectory branching properties. We have tested these methods for a molecule radiolysis decay problem. We found these methods can be used to study such radiolysis problem in which the molecule is broken into many fragments following complex electronic structure transition paths. The computational time of NOB is similar to the original plain rt-TDDFT simulations

scholarly journals Optical and Electronic Properties of Organic NIR-II Fluorophores by Time-Dependent Density Functional Theory and Many-Body Perturbation Theory: GW-BSE Approaches

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2293
Author(s):  
Nguyet N. T. Pham ◽  
Seong Hun Han ◽  
Jong S. Park ◽  
Seung Geol Lee
Keyword(s):  
Density Functional Theory ◽  
Perturbation Theory ◽  
Electronic Properties ◽  
Density Functional ◽  
Time Dependent ◽  
Many Body ◽  
Functional Theory ◽  
Optical And Electronic Properties ◽  
Many Body Perturbation Theory ◽  
Dependent Density

Organic-molecule fluorophores with emission wavelengths in the second near-infrared window (NIR-II, 1000–1700 nm) have attracted substantial attention in the life sciences and in biomedical applications because of their excellent resolution and sensitivity. However, adequate theoretical levels to provide efficient and accurate estimations of the optical and electronic properties of organic NIR-II fluorophores are lacking. The standard approach for these calculations has been time-dependent density functional theory (TDDFT). However, the size and large excitonic energies of these compounds pose challenges with respect to computational cost and time. In this study, we used the GW approximation combined with the Bethe-Salpeter equation (GW-BSE) implemented in many-body perturbation theory approaches based on density functional theory. This method was used to perform calculations of the excited states of two NIR molecular fluorophores (BTC980 and BTC1070), going beyond TDDFT. In this study, the optical absorption spectra and frontier molecular orbitals of these compounds were compared using TDDFT and GW-BSE calculations. The GW-BSE estimates showed excellent agreement with previously reported experimental results.

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