Thomas

Nicht wir, sondern die Sonne ist schuld an der globalen Erwärmung? Schlimm, dass es Menschen gibt, die solch krassen Unsinn ernst nehmen, kommentiert Klimatologe Stefan Rahmstorf.

Weltrekord: Zum ersten Mal haben Forscher eine chemische Reaktion bei nur 500 milliardstel Kelvin über dem absoluten Temperaturnullpunkt ablaufen lassen.

The Journal of Chemical Physics, Volume FEMTO2019, Issue 1, December 2019.
Based on the original Stochastic Surrogate Hamiltonian approach for the simulation of open quantum system dynamics, we present a modified algorithm for the swap procedure. The implementation is tested with nuclear relaxation dynamics of model systems known from literature, i.e., the harmonic oscillator and the Morse oscillator. Finally, the stochastic surrogate Hamiltonian is applied to simulate the dynamical electronic excitation and relaxation of a photodesorption process. This is the first application of the stochastic surrogate Hamiltonian in an ab initio context. A comparison to a surrogate Hamiltonian benchmark allows us to evaluate the results obtained. For this purpose, the well-studied laser-induced desorption of NO from NiO(100) is chosen.

The Journal of Chemical Physics, Volume 151, Issue 16, October 2019.
The attraction density functional theory (DFT) has for electronic structure theory is that it is easier to do computationally than ab initio, correlated wavefunction methods, due to its effective one-particle structure. On the contrary, ab initio theorists insist on the ability to converge to the right answer in appropriate limits, but this requires a treatment of the reduced two-particle density matrix. DFT avoids that by appealing to an “existence” theorem (not a constructive one) that all its effects are subsummed into a DFT functional of the one-particle density. However, the existence of thousands of DFT functionals emphasizes that there is no satisfactory way to systematically improve the Kohn-Sham (KS) version as most changes in parameterization or formulation seldom lead to a new functional that is genuinely better than others. Some researchers in the DFT community try to address this issue by imposing conditions rigorously derived from exact DFT considerations, but to date, no one has shown how this route will ever lead to converged results even for the ground state, much less for all the other electronic states obtained from time-dependent DFT that are critically important for chemistry. On the contrary, coupled-cluster (CC) theory and its equation-of-motion extensions provide rigorous results for both that KS-DFT methods are attempting to emulate. How to use them and their exact formal properties to tie CC theory to an effective one-particle form is the target of this perspective. This route addresses the devil’s triangle of KS-DFT problems: the one-particle spectrum, self-interaction, and the integer discontinuity.

The Journal of Chemical Physics, Volume OSQD2019, Issue 1, November 2019.
A comprehensive approach to modeling open quantum systems consistent with thermodynamics is presented. The theory of open quantum systems is employed to define system bath partitions. The Markovian master equation defines an isothermal partition between the system and bath. Two methods to derive the quantum master equation are described: the weak coupling limit and the repeated collision model. The role of the eigenoperators of the free system dynamics is highlighted, in particular, for driven systems. The thermodynamical relations are pointed out. Models that lead to loss of coherence, i.e., dephasing are described. The implication of the laws of thermodynamics to simulating transport and spectroscopy is described. The indications for self-averaging in large quantum systems and thus its importance in modeling are described. Basic modeling by the surrogate Hamiltonian is described, as well as thermal boundary conditions using the repeated collision model and their use in the stochastic surrogate Hamiltonian. The problem of modeling with explicitly time dependent driving is analyzed. Finally, the use of the stochastic surrogate Hamiltonian for modeling ultrafast spectroscopy and quantum control is reviewed.

The Journal of Chemical Physics, Volume 151, Issue 13, October 2019.
Based on the original Stochastic Surrogate Hamiltonian approach for the simulation of open quantum system dynamics, we present a modified algorithm for the swap procedure. The implementation is tested with nuclear relaxation dynamics of model systems known from literature, i.e., the harmonic oscillator and the Morse oscillator. Finally, the stochastic surrogate Hamiltonian is applied to simulate the dynamical electronic excitation and relaxation of a photodesorption process. This is the first application of the stochastic surrogate Hamiltonian in an ab initio context. A comparison to a surrogate Hamiltonian benchmark allows us to evaluate the results obtained. For this purpose, the well-studied laser-induced desorption of NO from NiO(100) is chosen.