Abstract

In the thirty-two years since the birth of the foundational theorems, time-dependent density functional theory has had a tremendous impact on calculations of electronic spectra and dynamics in chemistry, biology, solid-state physics, and materials science. Alongside the wide-ranging applications, there has been much progress in understanding fundamental aspects of the functionals and the theory itself. This Perspective looks back to some of these developments, reports on some recent progress and current challenges for functionals, and speculates on future directions to improve the accuracy of approximations used in this relatively young theory.

Highlights

  • The wavefunction rose from the early days of quantum mechanics as the central player, the provider of all observable properties of atoms, molecules, and solids

  • In the thirty-two years since the birth of the foundational theorems, time-dependent density functional theory has had a tremendous impact on calculations of electronic spectra and dynamics in chemistry, biology, solid-state physics, and materials science

  • In 1984 Erich Runge and Hardy Gross proved that for time-dependent (TD) systems evolving from a given initial wavefunction, all TD properties can be extracted from the time-evolving density

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Summary

INTRODUCTION

The wavefunction rose from the early days of quantum mechanics as the central player, the provider of all observable properties of atoms, molecules, and solids. Almost 40 years later, the Hohenberg-Kohn theorem proved that the ground-state density alone provides all observable properties of any static system This is an astonishing result given the simplicity of the density, the probability of finding any one electron at a given point in space, compared with the wavefunction, a function of all electronic coordinates. Given that Hohenberg, Kohn, and Sham had derived such a potential for an electron in a ground-state twenty years earlier, it was natural to wonder whether such a formulation could be extended to the timedependent case, yielding the exact time-dependent potential acting on an electron. This led to the birth of the foundational theorem of TDDFT, the Runge-Gross theorem.. I have brazenly ignored allimportant computational concerns, numerical aspects, details, and algorithms

DENSITY-POTENTIAL MAPPING
The TD Kohn-Sham system
Solving an existential crisis leads to alternative mapping proofs
EXCHANGE-CORRELATION POTENTIALS
The exact TD KS potential
The exact xc potential
The adiabatically exact approximation
Known exact conditions
EXCITATION SPECTRA
Challenging excitations
Rydberg excitations
Double excitations
Long-range charge-transfer excitations
Conical intersections
Optical response of solids
Molecular conductance
FULLY NON-LINEAR DYNAMICS
Challenges
Coupled electron-ion dynamics
OUTLOOK
Full Text
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