Navigation

Theoretical Chemistry

Overview

Theoretical Chemistry is part of the Department of Chemisty and comprises the research groups of Prof. Dr. Andreas Görling and of Prof. Dr. Dirk Zahn. The Görling group is a leader in the development of novel density-functional methods with unprecedented accuracy and wide applicability.  The group has been actively involved in the development of the widely used quantum chemistry codes Molpro and  TURBOMOLE and has been developing the electronic structure code MCEXX for periodic systems. A second field of activity are applications of electronic structure programs in  fields comprising molecular chemistry, catalysis, surface science, solid state physics, and materials science. The Zahn group takes a lead role in investigating self-organization processes and is devoted to the development and application of static and molecular dynamics simulations. Investigating the mechanisms of reactions, nucleation events and the assembly of nanosystems, the addressed topics range from materials science, solid state chemistry to biophysics and general physical chemistry.

People

Prof. Dr. Dirk Zahn

Email: dirk.zahn@fau.de

Görling group

Methods and Software

The group uses static electronic structure methods (density-functional theory, wave-function-based methods) and Ab-initio molecular dynamics simulations.
Used software packages are:
For research self-written special purpose software (e.g., for the homogeneous electron gas, for simulating and visualizing infrared spectra on surfaces) is employed.

Research Projects

Novel density-functional methods based on the adiabatic-connection fluctuation-dissipation (ACFD) theorem

Conventional DFT (density-functional theory) methods use functionals of the electron density to calculate the exchange and correlation energy. ACFD methods calculate the exchange energy exactly from occupied orbitals and approximate the correlation energy with the help of the ACFD theorem from response functions that depend on occupied as well as unoccupied orbitals and their eigenvalues. The electron density is not required in ACFD methods. What is needed instead, is the formal framework of DFT in particular the KS formalism. The simplest ACFD method amounts to the well-known random phase approximation for the correlation energy. More advanced ACFD approaches have been shown to yield unprecedented accuracy rivaling that of high level wave-function-based methods at a much lower computational effort. Moreover, some ACFD methods have been shown to be applicable to challenging electronic structures characterized by static/strong correlation.

Exact-exchange methods for taking into account spin-orbit interactions and the electronic temperature in semiconductors and topological insulators

Starting point are exact exchange Kohn-Sham methods using plane-wave basis sets and pseudopotentials to treat the core electrons. Relativistic effects, in particular spin-orbit interactions, can be introduced via the pseudopotentials. From a formal point of view, not only the electron density but additionally currents of the magnetization have to be used as basis variables in a DFT description in this case. An rigorous inclusion of magnetization currents is possible at the exact-exchange level. Similarly, effects due to a non-zero electronic temperature can be taken into account rigorously in an exact exchange framework. While these effects in most semiconductors play a minor role this is different in cases of semiconductors with very small band gaps or in topological insulators.

Carbon-rich materials

Within the collaborative research center 958 “Synthetic Carbon Allotropes” carbon-rich molecular compounds and two-dimensional materials are investigated. DFT calculations are used to predict new materials and their properties, to develop strategies for their synthesis, to characterize electronic properties, and to simulate spectroscopic data.

Catalysis at liquid interfaces

Novel catalysis concepts utilizing interfaces are explored. These comprise SCALMS (Supported Catalytically Active Liquid Metal Solutions, Interface-Enhanced SILP (Supported Ionic Liquid Phase, and Advanced SCILL (Solid Catalyst with Ionic Liquid Layer). Static DFT calculation are used to characterize catalytic cycles and electronic structures of the constituents of the catalytic setups. Ab-initio molecular dynamics simulations are used to determine correlation functions and diffusion coefficients in liquid metal alloys and to studiy surface depletion and enrichment effect of catalytically active atoms. Besides providing data to analyse experimental data, the knowledge based optimization of  catalytic setup is a key goal.

Chemical storage of solar energy

By converting molecules with sun light into isomers with higher energy, solar energy can be stored. The system norbornadiene/quadricyclane is an example for such a pair of isomeres. By chemical modification, e.g. by functionalization, such storage systems for solar energy shall be optimized. Electronic structure calculations contribute to this goal by providing insight into optical properties and by elucidating conversion mechanisms and their energetics.

Liquid organic hydrogen carriers (LOHCs)

LOHCs are organic molecules that can bind and release hydrogen reversibly. The energetics and kinetics of the hydrogen upload and release reactions are key quantities to be understood and subsequently optimized with the help of electronic structgure calculations. The stability of LOHCs is another key factor that determines the number of storage and release cycles that can be carried out with an LOHC.  An investigation of unwanted side reactions by electronic structure calculations can help to get insight on this point.

Selected Publications

Novel DFT methods based on the ACFD theorem

  • A. Görling, Hierarchies of methods towards the exact Kohn-Sham correlation energy based on the adiabatic-connection fluctuation-dissipation theorem, Phys. Rev. B 99, 235120 (2019).
  • A. Thierbach, D. Schmidtel and A. Görling, Robust and Accurate Hybrid Random-Phase-Approximation Methods,  J. Chem. Phys.151, 144117 (2019).
  • J. Erhard, P. Bleiziffer and A. Görling, Power series approximation for the correlation kernel leading to Kohn-Sham methods combining accuracy, computational efficiency, and general applicability, Phys. Rev. Lett. 117, 143002 (2016).
  • P. Bleiziffer, A. Heßelmann and A. Görling, Resolution of identity approach for the Kohn-Sham correlation energy within the exact-exchange random-phase approximation, J. Chem. Phys.136, 134102 (2012).
  • A. Heßelmann and A. Görling, Correct Description of the Bond Dissociation Limit without Breaking Spin Symmetry by a Random-Phase-Approximation Correlation Functional, Phys. Rev. Lett. 106, 093001 (2011).

Exact-exchange methods for taking into account spin-orbit interactions and the electronic temperature in semiconductors and topological insulators

  • E. Trushin, L. Fromm and A. Görling, Assessment of the exact-exchange-only Kohn-Sham method for the calculation of band structures for transition metal oxide and metal halide perovskites, Phys. Rev. B 100, 075205 (2019).
  • E. Trushin and A. Görling, Topological phase transitions in zinc-blende semimetals driven exclusively by electronic temperature, Phys. Rev. Lett. 120, 146401 (2018).

Carbon-rich materials

  • P. Vecera, J. C. Chacón-Torres, T. Pichler, S. Reich, H. R. Soni, A. Görling, K. Edelthalhammer, H. Peterlik, F. Hauke
    und A. Hirsch, Precise determination of graphene functionalization by in situ Raman spectroscopy, Nat. Commun. 8, 15192 (2017).
  • C. Steiner, J. Gebhardt, M. Ammon, Z. Yang, A. Heidenreich, N. Hammer, A. Görling, M. Kivala und S. Maier, Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures, Nat. Commun. 8, 14765 (2017).
  • D. Malko, F. Viñes, C. Neiss und A. Görling, Competition for graphene: graphynes with directional-dependent Dirac cones, Phys. Rev. Lett. 108, 086804 (2012).

Catalysis at liquid interfaces

  • T. Bauer, S. Maisel, D. Blaumeiser, J. Vecchietti, N. Taccardi, P. Wasserscheid, A. Bonivardi, A. Görling und J. Libuda, Operando DRIFTS and DFT study of propane dehydrogenation over solid and liquid supported xPty Catalysts, ACS Cat. 9, 2842-2853 (2019).
  • N. Taccardi, M. Grabau, J. Debuschewitz, M. Distaso, M. Brandl, R. Hock, F. Maier, C. Papp, J. Erhard, C. Neiss, W. Peukert, A. Görling, H.-P. Steinrück, P. Wasserscheid Gallium-rich Pd-Ga phases as supported liquid metal catalysts, Nat. Chem. 9, 862-867 (2017).

Chemical storage of solar energy

  •  C. Schuschke, C. Hohner,  M. Jevric, A. U. Petersen, Z. Wang, M. Schwarz, M. Kettner, F. Waidhas, L. Fromm,  C. Sumby, A. Görling, O. Brummel, K. Moth-Poulsen, J. Libuda, Solar energy storage at an atomically defined organic-oxide hybrid interface, Nat. Comm. 10, 2384 (2019).
  • F. Waidhas, M. Jevric, L. Fromm,  M. Bertram, A. Görling, K. Moth-Poulsen, O. Brummel, J. Libuda, Electrochemically Controlled Energy Storage in a Norbornadiene-Based Solar Fuel with 99% Reversibility Nano Energy, 63, UNSP 103872 (2019).

Liquid organic hydrogen carriers (LOHCs)

  • P. Bachmann, J. Steinhauser, F. Späth, F. Düll, U. Bauer, R. Eschenbacher, F. Hemauer, M. Scheuermeyer, A. Bösmann, M. Büttner, C. Neiss, A. Görling, P. Wasserscheid, H.-P. Steinrück und C. Papp, Dehydrogenation of the Liquid Organic Hydrogen Carrier  System 2-methylindole/2-methylindoline/2-methyloctahydroindole on Pt(111), J. Chem. Phys. 151, 144711 (2019).

Zahn Group

Methods and Software

The group uses static electronic structure methods (density-functional theory, wave-function-based methods), classical (empirical interaction models) molecular dynamics simulations, quantum/classical approaches and molecular modelling packages.

Used software packages are:

For QM/MM modelling we typically use LAMMPS scripts interfacing with dedicated QM calculations.

Research Projects

Reactions in complex Systems

We explore the mechanisms of reactions in condensed phases from quantum/ classical and ab-initio molecular dynamics simulations. A special focus is dedicated to proton transfer reactions occurring during crystal aggregation and ripening.

Self-Organization of Crystals, Macro-molecules and Composites

Starting from the association of single ions our simulations allow the investigation of the infancy of crystal nucleation from solution. This provides a unique level of insights into (self)-organization and its interplay with ripening reactions and interactions to growth-controlling molecules. The latter aspect allows also the investigation of hybrid materials.

Phase Transitions and Phase Separation

Our studies of phase transitions involve solid-solid, liquid-solid and liquid-vapor transformations. The main focus is dedicated to the mechanisms of phase nucleation and growth. In multinary systems also the interplay of phase transformation with segregation phenomena is explored (distillation, crystallization of eutectic systems).

Materials Simulations

Atomistic and coarse-grained models are used to explore the structure and mechanical properties of nano-crystals and bulk materials. These studies include atomic mobility, defect arrangements, dislocations, grain and phase boundaries as well as their role during deformation and fracture.

Sampling Bio-molecular Systems

The immense complexity of bio-molecular processes calls for advanced molecular dynamics protocols to assess the mechanisms and structures involved. We develop new simulation techniques to study biomolecule solvation, folding and docking to ligands without imposing restraints on protein flexibility or the arrangement of the solvent.

Method Development

The investigation of rare barrier crossing events (reactions, nucleation processes) requires efficient simulation strategies. To tackle the time/length scale problem we apply transition path sampling, constraint MD simulations and related approaches. Diffusion controlled processes, like crystal aggregation from dillute solutions impose different challenges to computer simulation. For this purpose, we develop specific approaches which allow to study aggregation and growth at the atomistic level of detail.

Force-Field Development

To enable molecular mechanics or efficient QM/MM modelling at high accuracy we develop tailor-made force-fields to extend the scope of off-the-shelf models where needed. Examples are molecular mechanics models of the different states of photo-switches and molecules before/after (de)protonation reactions. Moreover, for the prospering field of modelling additives in oil and at oil-steel interfaces, our OilF force-field is continuously extended to enable the molecular simulation of anti-wear films, debris dispergion and tribology at the nm scale.

Selected Publications

Reactions in complex Systems

  • P. Becker, T. Wonglakhon, D. Zahn, D. Gudat, R. Niewa, Approaching Dissolved Species in Ammonoacidic GaN Crystal Growth: A Combined Solution NMR and Computational Study, Chem.Eur.J., in press.
  • H.P. Huinink, S. Sansotta, D. Zahn, Defect-driven water migration in MgCl2 tetra- and hexahydrates, J. Solid State Chem., 277, 221-228. (2019)

Self-Organization of Crystals, Macro-molecules and Composites

  • M.Burraschi, S.Sansotta, D.Zahn, Polarization Effects in Dynamic Interfaces of Platinum Electrodes and Ionic Liquid Phases: a Molecular Dynamics Study, J. Phys. Chem. C.,  124, 3, 2002-2007. (2020)
  • P.Duchstein, P.Ectors and D.Zahn, Molecular simulations of crystal growth: From understanding to tailoring, Advances in Inorganic Chemistry, 73, 507-529. https://doi.org/10.1016/bs.adioch.2018.11.004 (2019)

Phase Transitions and Phase Separation

  • H.Park, A.May, L.Portilla, H.Dietrich, F.Münch, T.Rejek, M.Sarcletti, L.Banspach, D.Zahn and M.Halik, Simple and efficient magnetic removal of glyphosate from water, Nature Sustainability, in press. https://doi:10.1038/s41893-019-0452-6
  • M.Sarcletti, H.Dietrich, T.Luchs, D.Vivod, T.Rejek, L.Portilla, D.Zahn, A.Hirsch and M.Halik, Superoleophilic magnetic iron oxide nanoparticles for effective hydrocarbon removal from water, Adv. Funct. Mater. , 29, 1805742. https://doi.org/10.1002/adfm.201805742 (2019)

Materials Simulations

  • B.Becit, P.Duchstein, D.Zahn, Molecular mechanisms of mesoporous silica formation from colloid solution: ripening-reactions arrest hollow network structures, PLOS One,  14, e0212731. (2019)
  • J.Wittmann, C.Henkel, J.Träg, J.Will, L.Stiegler, P.Strohriegl, A.Hirsch, T.Unruh, D.Zahn, D.M. Guldi, M.Halik, Mixed Organic Ligand Shells: Controlling the Nanoparticle Surface Morphology towards Tuning the Optoelectronic Properties, Small, 16, 1903729. (2020)

Sampling Biomolecular Systems

  • C.Debus, B.Wu, T.Kollmann, P.Duchstein, M.Siglreitmeier, S.Herrera, D.Benke,D.Kisailus, D.Schwahn, V.Pipich, D.Faivre, D.Zahn, H.Cölfen, Bio-inspired Multifunctional Layered Magnetic Hybrid Materials, Bioinspired Biomimetic and Nanobiomaterials,  8, 1-66. (2019)
  • J.Träg, P.Duchstein, M.Hennemann, T.Clark, D.M.Guldi, D.Zahn, Size-Dependent Local Ordering in Melanin Aggregates and its Implication on Optical Properties, J.Phys.Chem.A, 123, 9403-9412 (2019)

Method Development

  • D.Zahn, On the solvation of metal ions in liquid ammonia: a molecular simulation study of M(NH2)x(NH3)y complexes as functions of pH, RSC Advances, 7, 54063-54067. (2017)
  • J.Anwar, D.Zahn, Polymorphic Phase Transitions: Macroscopic Theory and Molecular Simulation, Advanced Drug Delivery Reviews, 117, 47-70. (2017)

Force-Field Development

  • T.Wonglakhon, D.Zahn, Interaction Potentials for modelling GaN precipitation and solid state polymorphism, J.Phys.:Cond.Mat. in press.
  • P.Ectors, D.Zahn, Benchmarking and optimization of molecular simulation models of zinc dialkyldithio-phosphate and calcium sulfonate oil additives, J.Mol.Model., 25, 100. (2019)