(Quelle: SFB ViCoM Vienna Computational Materials Laboratory Proposal SFB Vicom / Application for the 2nd funding period, Spezialforschungsbereich F41)
During the last decades, computational science has firmly established its role as an important research tool complementing experimental and theoretical investigations. In particular, in materials science and condensed matter physics, where computer-aided studies now play a central role, unimagined possibilities have opened. Progress in this field has been so fast that many present-day applications could not have been realized ten years ago and were hardly imaginable thirty years ago. Although these developments have been facilitated by a rapidly increasing computer performance, the impact of novel theoretical methods in quantum mechanics and statistical mechanics, of improved computational algorithms, and of their implementation in highly efficient computer codes has been even more important. With the widening application of computational methods to problems of both fundamental science and modern technology, computational materials science continues to face new critical challenges:
(i) The prediction of groundstate total energies, of activation energies for chemical reactions and of phase transformations must achieve chemical accuracy. This requires a substantially improved treatment of many-electron correlation effects beyond the commonly used density functional theory approximation. Here, the recent developments in many-body physics, as well as in quantum chemistry have opened new routes. However, achieving this goal for realistic solid state materials is much more difficult.
(ii) To maintain the contact with modern experimental materials science and condensed matter physics, the functionality of the existing computer-simulation codes must be extended. Detailed predictions of materials properties that can be measured by electronic, optical or magnetic spectroscopies in weak and strong fields must become possible.
(iii) Even with the help of high-performance computers, the time and lengths scales accessible in the computer-laboratory are many orders of magnitude below those of real-world problems. To bridge these gaps requires the development of multi-scale simulation methods.
Scientists at the two large universities in Vienna, the University of Vienna and the Vienna University of Technology, together with their research partners at the TU Graz, have made over many years important contributions to the recent progress in computational materials science. In the Special Research Program (SFB) Vienna Computational Materials Laboratory (ViCoM), they combine their forces with the objective to address the three challenges outlined above. In this way, Vienna can consolidate its role as one of the leading centres in this research field. iv General Part
-Dynamical mean-field theory and beyond (Arrigoni, 01.06.2010-31.12.2018)
In the second funding period we plan to further improve the interface between density
functional theory (DFT) which is the workhorse of the SFB ViCoM and dynamical mean field
theory (DMFT) which accounts for a major part of the electronic correlations, i.e. the local ones.
We will continue to study non-local correlations beyond DMFT on all length scales and extend
our project into a new direction: the interplay of non-equilibrium and electronic correlations.
These three subprojects in more detail:
(1) DFT+DMFT interface: We plan a substantial extension of the wien2wannier package
including a DFT+DMFT self-consistency for the (hermitianized) self-energy a la Schilfgaarde
and Kotani, and of woptics, a package for calculating the optical spectra and other transport
properties. There are strong interconnections with P02 and P07 and their electronic structure
packages VASP and Wien2K; and with P16's mapping onto low-energy effective models.
(2) Non-local correlations beyond DMFT: the focus is on magnetic fluctuations in layered bulk
4d and 5d materials such as ruthenates and iridates. The latter are structurally similar to
cuprates, but with important multiorbital effects, and we will analyze whether magnetic
fluctuations can lead to similar pseudogap physics. We will also study the interplay between
spin-orbit coupling and electronic correlations and magnons. We will continue the
collaborations on impurity solvers with P04, regarding pseudogap physics we will profit from
the expertise of P16.
(3) Correlated interfaces out of equilibrium: We are interested in transport beyond linear
response theory across correlated interfaces and heterostructures. We will adopt a newly
developed nonequilibrium DMFT scheme, and parameters will be extracted from ab-initio calculations. Among other aspects, we are interested in transition metal oxide solar cells. We
will collaborate with P04 on non-equilibrium methods and P15 on heterostructures.
-Quantum Impurity Solvers (Evertz, 01.06.2010-31.12.2018)
The project aims at calculating spectral functions and real time evolution of the quantum many body problems of quantum impurity models and at understanding the correlations and entanglement of these models. In the first funding period we have successfully developed new zero-temperature quantum impurity solvers for single orbital and two-orbital impurities with very good energy resolution at all frequencies, based on Chebyshev expansions and on real time evolution using Matrix Product State (MPS) techniques. In the second funding period, we will extend and apply these techniques to larger multi-orbital models, to finite temperatures, and especially to non-equilibrium calculations and to the study of transport phenomena, in close collaboration with several other subprojects.
(1) Simulation of multi-band impurity models, especially transition metal oxides. Investigation of, e.g, the interplay of electronic correlations and spin-orbit coupling.
(2) Development of generalized impurity solvers. We will extend the applicability of the impurity solvers to finite temperatures, with density matrix renormalization group (DMRG) techniques and with a new Lagrangian approach, and calculate finite temperature spectral functions. We plan to include spatial correlations by incorporating a higher dimensional generalization of DMRG into the impurity solver.
(3) Non-equilibrium and transport. We will use the capabilities for real time evolution to study transport across heterostructures, the thermoelectric effect, scattering, and embedded clusters. We will generalize our impurity solver to the auxiliary master equation approach for non-equilibrium DMFT and apply it to low dimensional real time evolution, as well as to the exciting physics of the photovoltaic effect in oxide heterostructures and the corresponding recently proposed solar cells.
-Collective Phenomena in Oxide Films and Heterostructures (Boeri, 01.01.2015-31.12.2018)
Collective Phenomena in Oxide Films and Hetero-structures
Perovskite interfaces and heterostructures are at the core of next-generation nanoelectronics due to the unprecedented wealth of functionalities arising from the intermingled action of lattice, orbital, and electronic degrees of freedom. The theoretical description of these systems requires methods at the frontier of materials modeling. Our main objective is the computational study of collective phenomena in surfaces, interfaces and heterostructures of transition metal oxide (TMO) perovskites: we aim at first understanding the interplay among dimensional confinement, electronic correlations, spin-orbit coupling (SOC) and electron-lattice interactions, and then at exploiting our understanding for future materials design. For this, we will employ a combination of the most advanced ab-initio and many-body model methods developed within the ViCoM. In fact, correlated surfaces, interfaces, and multilayer heterostructures represent one of the best examples where purely ab-initio or model approaches only allow to describe a few aspects. Highly optimized structures, lattice dynamics, ab-initio low-energy, interacting Hamiltonians and, eventually, dynamical correlations are all necessary for a complete description.