
Michael BonitzKiel University | CAU · Institute for Theoretical Physics and Astrophysics (ITAP)
Michael Bonitz
Dr. rer. nat. habil. Dr. h.c.
About
635
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Introduction
My research focuses on non-ideal many-body systems--from low-temperature plasmas and plasma-surface interaction to astrophysical an condensed matter systems, warm dense matter and cold atomic gases. I also study finite systems in traps and optical lattices. Of special interest are quantum and spin effects, Coulomb correlations, collective effects, transport properties and the ultra-fast response to external excitations.. I develop analytical theories and first-principle classical and quantum computer simulations. For details see the publications, books and web page.
Publications
Publications (635)
Dense quantum plasmas out of equilibrium are successfully modeled using quantum kinetic equations, such as the quantum Boltzmann, Landau or Balescu-Lenard equation. However, these equations do not properly take into account correlation effects which requires to use generalized non-Markovian kinetic equations. While the latter have been successful f...
The exploration of ultrafast phenomena is a frontier of condensed matter research, where the interplay of theory, computation, and experiment is unveiling new opportunities for understanding and engineering quantum materials. With the advent of advanced experimental techniques and computational tools, it has become possible to probe and manipulate...
We present extensive new \emph{ab initio} path integral Monte Carlo (PIMC) simulation results for the chemical potential of the warm dense uniform electron gas (UEG), spanning a broad range of densities and temperatures. This is achieved by following two independent routes, i) based on the direct estimation of the free energy [Dornheim \emph{et al....
Accurate knowledge of the properties of hydrogen at high compression is crucial for astrophysics (e.g., planetary and stellar interiors, brown dwarfs, atmosphere of compact stars) and laboratory experiments, including inertial confinement fusion. There exists experimental data for the equation of state, conductivity, and Thomson scattering spectra....
Correlated classical and quantum many‐particle systems out of equilibrium are of high interest in many fields, including dense plasmas, correlated solids, and ultracold atoms. Accurate theoretical description of these systems is challenging both, conceptionally and with respect to computational resources. While for classical systems, in principle,...
Accurate knowledge of the properties of hydrogen at high compression is crucial for astrophysics (e.g. planetary and stellar interiors, brown dwarfs, atmosphere of compact stars) and laboratory experiments, including inertial confinement fusion. There exists experimental data for the equation of state, conductivity, and Thomson scattering spectra....
The theory of nonequilibrium Green functions (NEGF) has seen a rapid development over the recent three decades. Applications include diverse correlated many‐body systems in and out of equilibrium. Very good agreement with experiments and available exact theoretical results could be demonstrated if the proper selfenergy approximations were used. How...
Yuri L'vovich Klimontovich (September 28, 1924–October 26, 2002) was an outstanding theoretical physicist who made major contributions to kinetic theory. On the occasion of his 100th birthday, we recall his main scientific achievements.
Correlated quantum many‐particle systems out of equilibrium are of high interest in many fields, including correlated solids, ultracold atoms, or dense plasmas. Accurate theoretical description of these systems is challenging both, conceptionally and with respect to computational resources. A quantum fluctuations approach is recently presented, whi...
We present improved first-principle fermionic path integral Monte Carlo (PIMC) simulation results for a dense partially ionized hydrogen (deuterium) plasma, for temperatures in the range 15000K≤T≤400000K and densities 7×10−7g/cm3≤ρH≤0.085g/cm3 (1.4×10−6g/cm3≤ρD≤0.17g/cm3), corresponding to 100≥rs≥2, where rs=r¯/aB is the ratio of the mean interpart...
The quantum dynamics of correlated fermionic or bosonic many-body systems following external excitation can be successfully studied using nonequilibrium Green functions (NEGFs) or reduced density matrix methods. Approximations are introduced via a proper choice of the many-particle self-energy or decoupling of the BBGKY-hierarchy, respectively. The...
We present novel first-principle fermionic path integral Monte Carlo (PIMC) simulation results for a dense partially ionized hydrogen (deuterium) plasma, for temperatures in the range $15,000$K $\leq T \leq 400,000$K and densities $7 \cdot 10^{-7}$g/cm$^{3}\leq \rho_H \leq 0.085$ g/cm$^{3}$ ($1.4 \cdot 10^{-6}$g/cm$^{3}\leq \rho_D \leq 0.17$ g/cm$^...
In a recent Letter [T. Dornheim et al., Phys. Rev. Lett. 121, 255001 (2018)], it was predicted on the basis of ab initio quantum Monte Carlo simulations that, in a uniform electron gas, the peak ω0 of the dynamic structure factor S(q,ω) exhibits an unusual nonmonotonic wave number dependence, where dω0/dq<0, at intermediate q, under strong coupling...
We explore the nonequilibrium dynamics of a one-dimensional Fermi-Hubbard system as a sensitive testbed for the capabilities of the time-dependent two-particle reduced density matrix (TD2RDM) theory to accurately describe time-dependent correlated systems. We follow the time evolution of the out-of-equilibrium finite-size Fermi-Hubbard model initia...
The quantum dynamics of correlated fermionic or bosonic many-body systems following external excitation can be successfully studied using nonequilibrium Green functions (NEGF) or reduced density matrix methods. Approximations are introduced via a proper choice of the many-particle selfenergy or decoupling of the BBGKY-hierarchy, respectively. These...
Real-time nonequilibrium Green functions (NEGFs) have been very successfully used to simulate the dynamics of correlated many-particle systems far from equilibrium. However, NEGF simulations are computationally expensive since the effort scales cubically with the simulation duration. Recently, we introduced the G1–G2 scheme that allows for a dramat...
In a recent Letter [T. Dornheim \textit{et al.}, Phys. Rev. Lett. \textbf{121}, 255001 (2018)], it was predicted on the basis of \textit{ab initio} quantum Monte Carlo simulations that, in a uniform electron gas, the peak $\omega_0$ of the dynamic structure factor $S(q,\omega)$ exhibits an unusual non-monotonic wave number dependence, where $d\omeg...
Günter Kelbg did remarkable early work in the field of quantum statistical physics, in particular for dense quantum plasmas. In 2022 we celebrated his 100th birthday. On this occasion, we give a brief overview of his main scientific achievements in the field of quantum plasmas, complemented by some biographical background of his research and teachi...
Warm dense matter—an exotic, highly compressed state on the border between solid and plasma phases is of high current interest, in particular for compact astrophysical objects, high‐pressure laboratory systems, and inertial confinement fusion. For many applications, the interaction of quantum plasmas with energetic particles is crucial. Moreover, o...
We explore the non-equilibrium dynamics of a one-dimensional Fermi-Hubbard system as a sensitive testbed for the capabilities of the time-dependent two-particle reduced density matrix (TD2RDM) theory to accurately describe time-dependent correlated systems. We follow the time evolution of the out-of-equilibrium finite-size Fermi-Hubbard model initi...
Matter at extreme temperatures and pressures—commonly known as warm dense matter (WDM)—is ubiquitous throughout our Universe and occurs in astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion and is realized in the laboratory using d...
Warm dense matter--an exotic, highly compressed state on the boarder between solid and plasma phases is of high current interest, in particular for compact astrophysical objects, high pressure laboratory systems, and inertial confinement fusion. For many applications the interaction of quantum plasmas with energetic particles is crucial. Moreover,...
Magnetized plasmas are well known to exhibit a rich spectrum of collective modes. Here, we focus on the density modes in dense or cold plasmas, where strong coupling effects alter the mode spectrum known from traditional weakly coupled plasmas. In particular, we study the dynamic structure factor (DSF) of the magnetized one‐component plasma with mo...
Magnetized plasmas are well known to exhibit a rich spectrum of collective modes. Here, we focus on the density modes in dense or cold plasmas, where strong coupling effects alter the mode spectrum known from traditional weakly coupled plasmas. In particular, we study the dynamic structure factor (DSF) of the magnetized one-component plasma with mo...
Matter at extreme temperatures and pressures -- commonly known as warm dense matter (WDM) in the literature -- is ubiquitous throughout our Universe and occurs in a number of astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion, and...
The study of matter under extreme densities and temperatures as they occur, for example, in astrophysical objects and nuclear fusion applications has emerged as one of the most active frontiers in physics, material science, and related disciplines. In this context, a key quantity is given by the dynamic structure factor S ( q , ω ), which is probed...
Real-time nonequilibrium Green functions (NEGF) have been very successful to simulate the dynamics of correlated many-particle systems far from equilibrium. However, NEGF simulations are computationally expensive since the effort scales cubically with the simulation duration. Recently we have introduced the G1--G2 scheme that allows for a dramatic...
We compare the ion-induced electron emission from freestanding monolayers of graphene and MoS2 to find a sixfold higher number of emitted electrons for graphene even though both materials have similar work functions. An effective single-band Hubbard model explains this finding by a charge-up in MoS2 that prevents low energy electrons from escaping...
The quantum dynamics of fermionic or bosonic many-body systems following external excitation can be successfully studied using two-time nonequilibrium Green's functions (NEGF) or single-time reduced density matrix methods. Approximations are introduced via a proper choice of the many-particle self-energy or decoupling of the BBGKY hierarchy. These...
Dynamical screening is a key property of charged many-particle systems. Its theoretical description is based on the GW approximation that is extensively applied for ground-state and equilibrium situations but also for systems driven out of equilibrium. The main limitation of the GW approximation is the neglect of strong electronic correlation effec...
The quantum dynamics of fermionic or bosonic many-body systems following external excitation can be successfully studied using nonequilibrium Green functions (NEGF) or reduced density matrix methods. Approximations are introduced via a proper choice of the selfenergy or decoupling of the BBGKY-hierarchy. These approximations are based on Feynman's...
The study of matter under extreme densities and temperatures as they occur e.g. in astrophysical objects and nuclear fusion applications has emerged as one of the most active frontiers in physics, material science, and related disciplines. In this context, a key quantity is given by the dynamic structure factor $S(\mathbf{q},\omega)$, which is prob...
Plasmas in strong magnetic fields have been mainly studied in two distinct limiting cases—that of weak and strong nonideality with very different physical properties. While the former is well described by the familiar theory of Braginskii, the latter regime is closer to the behavior of a Coulomb liquid. Here we study in detail the transition betwee...
Dynamical screening is a key property of charged many-particle systems. Its theoretical description is based on the $GW$ approximation that is extensively applied for ground-state and equilibrium situations but also for systems driven out of equilibrium. The main limitation of the $GW$ approximation is the neglect of strong electronic correlation e...
Correlated many-fermion systems emerge in a broad range of phenomena in warm dense matter, plasmonics, and ultracold atoms. Quantum hydrodynamics (QHD) complements first-principles methods for many-fermion systems at larger scales. We illustrate the failure of the standard Bohm potential central to QHD for strong perturbations when the density pert...
We present extensive new ab initio path integral Monte Carlo (PIMC) results for an electron gas at warm dense matter conditions that is subject to multiple harmonic perturbations. In addition to the previously investigated nonlinear effects at the original wave number (Dornheim et al., Phys. Rev. Lett., 2020, 125, 085001) and the excitation of high...
In a recent Letter [Balzer et al., Phys. Rev. Lett. 121, 267602 (2018)] it was demonstrated that ions impacting a correlated finite graphene‐type honeycomb cluster can excite strongly nonequilibrium states. In particular, this can lead to an enhanced population of bound pairs of electrons with opposite spin — doublons — where the doublon number can...
Warm dense matter (WDM), an exotic, highly compressed state of matter between solid and plasma phases, is of high current interest, in particular for astrophysics and inertial confinement fusion. For the latter, in particular the propagation of compression shocks is crucial. The main unknown in the shock propagation in WDM is the behaviour of the e...
Plasmas in strong magnetic fields have been mainly studied in two distinct limiting cases--that of weak and strong nonideality with very different physical properties. While the former is well described by the familiar theory of Braginskii, the latter regime is closer to the behavior of a Coulomb liquid. Here we study in detail the transition betwe...
We present extensive new ab initio path integral Monte Carlo (PIMC) results for an electron gas at warm dense matter conditions that is subject to multiple harmonic perturbations. In addition to the previously investigated nonlinear effects at the original wave number [Dornheim \emph{et al.}, PRL \textbf{125}, 085001 (2020)] and the excitation of h...
In a recent Letter [Balzer \textit{et al.}, Phys. Rev. Lett. \textbf{121}, 267602 (2018)] it was demonstrated that ions impacting a correlated graphene cluster can excite strongly nonequilibrium states. In particular, this can lead to an enhanced population of bound pairs of electrons with opposite spin -- doublons -- where the doublon number can b...
Warm dense matter (WDM)--an exotic, highly compressed state of matter between solid and plasma phases is of high current interest, in particular for astrophysics and inertial confinement fusion. For the latter, in particular the propagation of compression shocks is crucial. The main unknown in the shock propagation in WDM is the behavior of the ele...
In a recent letter, Dornheim et al. [Phys. Rev. Lett. 125, 085001 (2020)] have investigated the nonlinear density response of the uniform electron gas in the warm dense matter regime. More specifically, they have studied the cubic response function at the first harmonic, which cannot be neglected in many situations of experimental relevance. In thi...
The uniform electron gas (UEG) is one of the key models for the understanding of warm dense matter—an exotic, highly compressed state of matter between solid and plasma phases. The difficulty in modelling the UEG arises from the need to simultaneously account for Coulomb correlations, quantum effects, and exchange effects, as well as finite tempera...
We study the time-dependent neutralization of a slow highly charged ion that penetrates a hexagonal hollow-centred graphene nanoflake. To compute the ultrafast charge transfer dynamics, we apply an effective Hubbard nanocluster model and use the method of nonequilibrium Green functions in conjunction with an embedding self-energy scheme, which allo...
In a classical plasma the momentum distribution, n(k), decays exponentially, for large k, and the same is observed for an ideal Fermi gas. However, when quantum and correlation effects are relevant simultaneously, an algebraic decay, n∞(k)∼k−8 has been predicted. This is of relevance for cross sections and threshold processes in dense plasmas that...
In a recent Letter, Dornheim et al. [PRL 125, 085001 (2020)] have investigated the nonlinear density response of the uniform electron gas in the warm dense matter regime. More specifically, they have studied the cubic response function at the first harmonic, which cannot be neglected in many situations of experimental relevance. In this work, we go...
Correlated many-fermion systems emerge in a broad range of phenomena in warm dense matter, plasmonics, and ultracold atoms. Quantum hydrodynamics (QHD) complements common first-principles methods for many-fermion systems and enables simulations at larger length and longer time scales. While the quantum Bohm potential is central to QHD, we illustrat...
We study the time-dependent neutralization of a slow highly charged ion that penetrates a hexagonal hollow-centred graphene nanoflake. To compute the ultrafast charge transfer dynamics, we apply an effective Hubbard nanocluster model and use the method of nonequilibrium Green functions (NEGF) in conjunction with an embedding self-energy scheme whic...
The energy gap of correlated Hubbard clusters is well studied for one‐dimensional systems using analytical methods and density‐matrix‐renormalization‐group (DMRG) simulations. Beyond 1D, however, exact results are available only for small systems by quantum Monte Carlo. For this reason and, due to the problems of DMRG in simulating 2D and 3D system...
The screening of a test charge by partially degenerate non‐ideal free electrons at conditions related to warm dense matter and dense plasmas is investigated using linear response theory and the local field correction based on ab initio Quantum Monte‐Carlo simulations data. The analysis of the obtained results is performed by comparing to the random...
We present a finite-temperature density-functional-theory investigation of the nonequilibrium transient electronic structure of warm dense Li, Al, Cu, and Au created by laser excitation. Photons excite electrons either from the inner shell orbitals or from the valence bands according to the photon energy, and give rise to isochoric heating of the s...
In a classical plasma the momentum distribution, $n(k)$, decays exponentially, for large $k$, and the same is observed for an ideal Fermi gas. However, when quantum and correlation effects are relevant simultaneously, an algebraic decay, $n_\infty(k)\sim k^{-8}$ has been predicted. This is of relevance for cross sections and threshold processes in...
Quantum Monte Carlo (QMC) belongs to the most accurate simulation techniques for quantum many-particle systems. However, for fermions, these simulations are hampered by the sign problem that prohibits simulations in the regime of strong degeneracy. The situation changed with the development of configuration path integral Monte Carlo (CPIMC) by Scho...
There is growing interest in warm dense matter (WDM), an exotic state on the border between condensed matter and plasmas. Due to the simultaneous importance of quantum and correlation effects, WDM is complicated to treat theoretically. A key role has been played by ab initio path integral Monte Carlo (PIMC) simulations, and recently extensive resul...
The screening of a test charge by partially degenerate non-ideal free electrons at conditions related to warm dense matter and dense plasmas is investigated using linear response theory and the local field correction based on ab inito Quantum Monte-Carlo simulations data. The analysis of the obtained results is performed by comparing to the random...
We present a finite-temperature density functional theory investigation of the nonequilibrium transient electronic structure of warm dense Li, Al, Cu, and Au created by laser excitation. Photons excite electrons either from the inner shell orbitals or from the valence bands according to the photon energy, and give rise to isochoric heating of the s...
Warm dense matter (WDM) is an exotic state on the border between condensed matter and dense plasmas. Important occurrences of WDM include dense astrophysical objects, matter in the core of our Earth, and matter produced in strong compression experiments. As of late, x‐ray Thomson scattering has become an advanced tool to diagnose WDM. The interpret...
Warm dense matter (WDM)—an extreme state with high temperatures and densities that occurs, e.g., in astrophysical objects—constitutes one of the most active fields in plasma physics and materials science. These conditions can be realized in the lab by shock compression or laser excitation, and the most accurate experimental diagnostics is achieved...
Warm dense matter (WDM) is an exotic state on the border between condensed matter and dense plasmas. Important occurrences of WDM include dense astrophysical objects, matter in the core of our Earth, as well as matter produced in strong compression experiments. As of late, x-ray Thomson scattering has become an advanced tool to diagnose WDM. The in...
There is growing interest in warm dense matter (WDM) -- an exotic state on the border between condensed matter and plasmas. Due to the simultaneous importance of quantum and correlation effects WDM is complicated to treat theoretically. A key role has been played by \textit{ab initio} path integral Monte Carlo (PIMC) simulations, and recently exten...
Quantum Monte Carlo belongs to the most accurate simulation techniques for quantum many-particle systems. However, for fermions, these simulations are hampered by the sign problem that prohibits simulations in the regime of strong degeneracy. The situation changed with the development of configuration path integral Monte Carlo (CPIMC) by Schoof \te...
The time evolution in quantum many-body systems after external excitations is attracting high interest in many fields, including dense plasmas, correlated solids, laser-excited materials, or fermionic and bosonic atoms in optical lattices. The theoretical modeling of these processes is challenging, and the only rigorous quantum-dynamics approach th...
The energy gap of correlated Hubbard clusters is well studied for one-dimensional systems using analytical methods and density-matrix-renormalization-group (DMRG) simulations. Beyond 1D, however, exact results are available only for small systems by quantum Monte Carlo. For this reason and, due to the problems of DMRG in simulating 2D and 3D system...
We investigate the energy-loss characteristics of an ion in warm dense matter (WDM) and dense plasmas concentrating on the influence of electronic correlations. The basis for our analysis is a recently developed ab initio quantum Monte Carlo– (QMC) based machine learning representation of the static local field correction (LFC) [Dornheim et al., J....
Warm dense matter (WDM)---an extreme state with high temperatures and densities that occurs e.g. in astrophysical objects---constitutes one of the most active fields in plasma physics and materials science. These conditions can be realized in the lab by shock compression or laser excitation, and the most accurate experimental diagnostics is achieve...
Warm dense matter (WDM)—an exotic state of highly compressed matter—has attracted increased interest in recent years in astrophysics and for dense laboratory systems. At the same time, this state is extremely difficult to treat theoretically. This is due to the simultaneous appearance of quantum degeneracy, Coulomb correlations, and thermal effects...