Excitonic effects in solids can be calculated using the Bethe-Salpeter equation (BSE) or the Casida equation of time-dependent density-functional theory (TDDFT). In both methods, the Tamm-Dancoff approximation (TDA), which decouples excitations and de-excitations, is widely used to reduce computational cost. Here, we study the effect of the TDA on exciton binding energies of solids obtained fro...

We present a range-separated linear-response time-dependent density-functional theory (TDDFT) which combines a density-functional approximation for the short-range response kernel and a frequency-dependent second-order Bethe-Salpeter approximation for the long-range response kernel. This approach goes beyond the adiabatic approximation usually used in linear-response TDDFT and aims at improving...

Excited-state calculations are implemented in a development version of the GPU-based TeraChem software package using the configuration interaction singles (CIS) and adiabatic linear response Tamm-Dancoff time-dependent density functional theory (TDA-TDDFT) methods. The speedup of the CIS and TDDFT methods using GPU-based electron repulsion integrals and density functional quadrature integration...

Time-dependent density functional theory (TDDFT) for quantummany-body systems on a lattice is formulated rigorously. We prove the uniqueness of the density-to-potential mapping and demonstrate that a given density is v representable if the initial many-body state and the density satisfy certain well-defined conditions. In particular, we show that for a system evolving from its ground state any ...

Adiabatic response time-dependent density functional theory (TDDFT) suffers from the restriction to basically an occupied → virtual single excitation formulation. Adiabatic time-dependent density matrix functional theory allows to break away from this restriction. Problematic excitations for TDDFT, viz. bonding-antibonding, double, charge transfer, and higher excitations, are calculated along t...

This chapter gives an overview of the description of the optical and dielectric properties of bulk insulators and semiconductors in time-dependent density-functional theory (TDDFT), with an emphasis on excitons. We review the linear-response formalism for periodic solids, discuss excitonic exchange-correlation kernels, calculate exciton binding energies for various materials, and compare the tr...

Closed expressions for nonadiabatic coupling between the ground and an excited electronic state of a molecule are derived by representing the time-dependent density functional ~TDDFT! equations in a form of classical dynamics for the Kohn-Sham ~KS! single-electron density matrix. Applicability of Krylov-space-type fast algorithms to nonadiabatic TDDFT as well as the representivity of the time-d...

The ground-state electronic and structural properties, and the electronic excitations of the lowest energy isomers of the Ag8 cluster are calculated using density functional theory (DFT) and timedependent DFT (TDDFT) in real time and real space scheme, respectively. The optical spectra provided by TDDFT predict that the D2d dodecahedron isomer is the structural minimum of Ag8 cluster. Indeed, i...

In this chapter, we review the recent new developments in time-dependent density functional (TDDFT) methods for treatment of dynamics of many-electron molecules in intense laser fields. We discuss some recent development of TDDFT with optimized effective potential (OEP) and self-interaction-correction (SIC) for many-electron systems which allows the use of orbital-independent single-particle lo...

Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this article we present the ongoing efforts for the parallelisation of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has a great potential for execution in...