# Dietrich FoersterUniversité Bordeaux 1 · Physics

Dietrich Foerster

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26

Publications

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Introduction

**Skills and Expertise**

## Publications

Publications (26)

The GW approximation for electronic excitations is considered computationally hard because its CPU time scales as O(N4) with the number N of atoms in the unit cell. The space time approach to this approximation scales, in principle, as O(N3), but for crystals it is nearly impossible to exploit this feature because it requires too much computer memo...

The electronic and optical properties of crystalline tetrathienophenazine derivatives (l-TTP, m-TTP, t-TTP) and their four fluorinated and brominated derivatives are predicted using density functional theory within the generalized gradient approximation and including the van der Waals weak interactions. We analyze how the position of sulfur atoms a...

We present a study of the optical response of compact and hollow icosahedral
clusters containing up to 868 silver atoms by means of time-dependent density
functional theory. We have studied the dependence on size and morphology of
both the sharp plasmonic resonance at 3--4 eV (originated mainly from
$sp$-electrons), and the less studied broader fea...

Ionization potentials (IPs) and electron affinities (EAs) are important quantities input into most models for calculating the open-circuit voltage (Voc) of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB) method with the third-order self-consistent charge (SCC) correction and the 3ob parameter set (the third...

A method is presented to compute the dielectric function for extended systems using linear response time-dependent density functional theory. Localized basis functions with finite support are used to expand both eigenstates and response functions. The electron-energy loss function is directly obtained by an iterative Krylov-subspace method. We appl...

The Bethe-Salpeter equation (BSE) is currently the state of the art in the
description of neutral electron excitations in both solids and large finite
systems. It is capable of accurately treating charge-transfer excitations that
present difficulties for simpler approaches. We present a local basis set
formulation of the BSE for molecules where the...

Two self-consistent schemes involving Hedin's $GW$ approximation are studied
for a set of sixteen different atoms and small molecules. We compare results
from the fully self-consistent $GW$ approximation (SC$GW$) and the
quasi-particle self-consistent $GW$ approximation (QS$GW$) within the same
numerical framework. Core and valence electrons are tr...

Two self-consistent schemes involving Hedin's GW approximation are studied for a set of sixteen different atoms and small molecules. We compare results from the fully self-consistent GW approximation (SCGW) and the quasiparticle self-consistent GW approximation (QSGW) within the same numerical framework. Core and valence electrons are treated on an...

Many-body perturbation theory of bulk systems is often realized within
reciprocal space, using plane-wave (PW) basis sets. PW basis is
advantageous because of its elementary basis functions and simple
convergence control. However, the number of functions in PW basis grows
with third power of unit cell size, irrespective of actual number of
atoms pr...

Hedin's GW approximation (GWA) is a well known method to study charged
excitations in electronic systems with a moderate computational cost
[1]. Already one-shot GWA delivers a considerable improvement if
compared with Green's functions from density-functional theory (DFT).
However, the one-shot results are dependent on the used starting point.
Thi...

We describe an implementation of Hedin's GW approximation for molecules and clusters, the complexity of which scales as O(N(3)) with the number of atoms. Our method is guided by two strategies: (i) to respect the locality of the underlying electronic interactions and (ii) to avoid the singularities of Green's functions by manipulating, instead, the...

Organic electronics is a rapidly developing technology. Typically, the
molecules involved in organic electronics are made up of hundreds of atoms,
prohibiting a theoretical description by wavefunction-based ab-initio methods.
Density-functional and Green's function type of methods scale less steeply with
the number of atoms. Therefore, they provide...

The diagram on the front cover illustrates the calculation of the self-energy in Hedin's GW approximation using a basis of dominant products. Such a basis is useful in conjunction with the LCAO ansatz for molecular orbitals. It notably simplifies the calculation of properties of excited states in TDDFT (time-dependent density functional theory), GW...

The use of the LCAO (Linear Combination of Atomic Orbitals) method for excited states involves products of orbitals that are known to be linearly dependent. We identify a basis in the space of orbital products that is local for orbitals of finite support and with a residual error that vanishes exponentially with its dimension. As an application of...

We describe a fast parallel iterative method for computing molecular
absorption spectra within TDDFT linear response and using the LCAO method. We
use a local basis of "dominant products" to parametrize the space of orbital
products that occur in the LCAO approach. In this basis, the dynamical
polarizability is computed iteratively within an approp...

We extend the LCAO (Linear Combination of Atomic Orbitals) method to excited states by constructing a particularly simple basis in the space of orbital products. The residual error of our procedure vanishes exponentially with the number of products and our procedure avoids auxiliary sets of fitting functions and their intrinsic ambiguities. As an a...

We construct the Kohn-Sham density response function chi(0) in a previously described basis of the space of orbital products. The calculational complexity of our construction is O(N(2)N(omega)) for a molecule of N atoms and in a spectroscopic window of N(omega) frequency points. As a first application, we use chi(0) to calculate the molecular spect...

We present a TDDFT code developed in the framework of NOSSI project. The code is capable to compute absorption spectra in linear response regime. The method for calculating of the Kohn-Sham response function is outlined. Complexity of the method is discussed in detail. Testing of the shared memory parallelization and examples of spectra are given.

We propose a direct method for reducing the dimension of the space of orbital products that occur, for example, in the calculation of time dependent density functional theory linear response and in Hedin's GW approximation to the electron propagator. We do this by defining, within the linear space of orbital products, a subspace of dominant directi...

The four center integrals needed in the Hartree Fock approximation and in TDDFT linear response are known to be difficult to calculate for orbitals of the Slater type or of finite range. We show that the interaction of pairs of products that do not mutually intersect may be replaced by the interaction of their moments, of which there are O(N). Only...

For hybrid systems, such as molecules grafted onto solid surfaces, the calculation of linear response in time dependent density functional theory is slowed down by the need to calculate, in ∼N4 operations, the susceptibility of N noninteracting Kohn-Sham reference electrons. We observe that in a basis of local orbitals this susceptibility can be ca...

To describe the metal-insulator transition in the oxide TlSr2CoO5, we investigate the electronic structure of its high-temperature tetragonal phase by the local density approximation (LDA) and model Hartree-Fock calculations. Within the LDA we find a homogeneous metallic and ferromagnetic ground state; however, when including the strong Coulomb int...

We consider spin-Peierls solitons in a Heisenberg model with static magneto elastic couplings. The NMR signal predicted by this model disagrees with existing NMR data on CuGeO3 by an order of magnitude, while the distribution of averaged spins agrees qualitatively with the data. Some extra dynamics appears to be needed for an adequate description o...

We compute the magnetic profile of spin Peierls solitons in a simple Heisenberg model with magneto elastic couplings, using independently the DMRG method and the Hartree Fock approximation. Our results agree qualitatively with published NMR data provided we average over the spin profiles. We conclude that he dynamics of the spin plus lattice system...

## Projects

Projects (2)

The building blocks of organic electronics and organic solar cells are organic semiconductors , a very large class of materials with of conjugated molecules as constituents. Predicting their main properties before synthesis could help to improve them. With this aim in mind, Saber Gueddida and I are extending an existing lower scaling GW algorithm from molecules to crystals. Promising results methods have already been obtained by Georg Kresse and co workers using different methods.