‪Thomas Frauenheim

‪Thomas Frauenheim

Chair Professor

Beijing Computational Science Research Center

Shenzhen JL Computational Science And Applied Research Institute

Biography

‪Thomas Frauenheim is a chair professor of computational material science at Shenzhen JL Computational Science And Applied Research Institute, Beijing Computational Science Research Center.

Education

  • PhD in Theoretical Physics, 1976

    Technical University Dresden

  • Diploma in Theoretical Solid State Physics, 1973

    Technical University Dresden

Research Projects

Coherent real-time charge transport across a donor−acceptor interface

We theoretically have studied the ultrafast charge transport in thiophene:fullerene stacks using time-dependent density functional tight-binding theory combined with Ehrenfest molecular dynamics for open systems. Our results reveal coherent oscillations of the charge density between neighboring donor sites, persisting for ∼200 fs and promoting charge transport within the polymer stacks.
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Coherent real-time charge transport across a donor−acceptor interface

DFTB+ Software development

DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods.
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DFTB+ Software development

Photo-induced real time spin dynamics in 2D magnets

Laser-induced switching of spins in materials is of great interest to revolutionize future magnetic storage technology and spintronics, which is generally realized in multicomponent ferrimagnetic (FiM) compounds but rare in 2D magnets.
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Photo-induced real time spin dynamics in 2D magnets

Photocatalysis on metal oxide surfaces

Femtosecond X-ray laser pulses synchronized with an optical laser were employed to investigate the dynamics of the photocatalytic oxidation of CO on the anatase TiO2(101) surface in real-time. Our results provide evidence of ultrafast timescales for the photooxidation of CO to CO2 and clarify the initial mechanism of oxygen activation that is crucial to unraveling the underlying processes for a range of photocatalytic reactions relevant to air purification and self-cleaning surfaces.
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Photocatalysis on metal oxide surfaces

TD-DFT/B real-time charge dynamics at hybrid interfaces

In a recent work, we have studied the photodynamic process in a supramolecular arrangement composed of a hydrogenated nanodiamond (C190H110) interacting with a 3,4,9,10-perylenetetra-carboxylic acid diimide (PDI) molecule as acceptor. After pulse irradiation in tune with the photoexcitation of the acceptor, the system shows an ultrafast charge transfer process reaching a stable steady state in a few tens of femtoseconds.
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TD-DFT/B real-time charge dynamics at hybrid interfaces

Ultrafast energy transfer through an intermolecular CoIn

Conical intersections (CoIns) of multidimensional potential energy surfaces are ubiquitous in nature and control pathways and yields of many photo-initiated intramolecular processes. Such topologies can be potentially involved in the energy transport in aggregated molecules or polymers but are yet to be uncovered.
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Ultrafast energy transfer through an intermolecular CoIn

Meet the Team in

Principal Investigators

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Chi-Yung YAM

Associate Professor

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‪Thomas Frauenheim

Chair Professor

Researchers

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Adriel Dominguez-Garcia

PostDoc

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Jun LI

PostDoc

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Tong MOU

PostDoc

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Xiaoyan WU

PostDoc

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Xingshuai LV

PostDoc

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Zhen TONG

PostDoc

Grad Students

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Yatian ZHANG

PostGraduate

Featured Publications

March 2020 J. Chem. Phys. 152, 124101 (2020)

DFTB+, a software package for efficient approximate density functional theory based atomistic simulations

DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green’s functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives.
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September 1998 Physical Review B

Self-consistent-charge density-functional tight-binding method for simulations of complex materials properties

We outline details about an extension of the tight-binding (TB) approach to improve total energies, forces, and transferability. The method is based on a second-order expansion of the Kohn-Sham total energy in density-functional theory (DFT) with respect to charge density fluctuations. The zeroth order approach is equivalent to a common standard non-self-consistent (TB) scheme, while at second order a transparent, parameter-free, and readily calculable expression for generalized Hamiltonian matrix elements may be derived. These are modified by a self-consistent redistribution of Mulliken charges (SCC). Besides the usual “band structure” and short-range repulsive terms the final approximate Kohn-Sham energy additionally includes a Coulomb interaction between charge fluctuations. At large distances this accounts for long-range electrostatic forces between two point charges and approximately includes self-interaction contributions of a given atom if the charges are located at one and the same atom. We apply the new SCC scheme to problems where deficiencies within the non-SCC standard TB approach become obvious. We thus considerably improve transferability.
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Recent Publications

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GW electronic structure calculations of cobalt defects in ZnO

Recently the point defect responsible for the emission of cobalt in doped zinc oxide (ZnO) samples has been identified [24]. In this work we extend our investigation to other point defects in Co-doped ZnO. We use density-functional theory and GW calculations to obtain the orbital-resolved band structure of cobalt doped ZnO. We show that mainly O-p and Co-d orbitals take part in the process and confirm that an oxygen interstitial nearby a cobalt atom is a likely defect to occur in ion beam Co-doped ZnO samples. We also rule out that other common point defects in ZnO can be responsible for the observed d-d transition. Finally, we suggest that defect complexes involving oxygen interstitials could be used to promote ferromagnetism in cobalt doped ZnO samples.
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Electron paramagnetic resonance and theoretical study of gallium vacancy in β-Ga2O3

Unintentionally doped n-type β-Ga2O3 becomes highly resistive after annealing at high temperatures in oxygen ambient. The annealing process also induces an electron paramagnetic resonance (EPR) center, labeled IR1, with an electron spin of S = 1/2 and principal g-values of gxx = 2.0160, gyy = 2.0386, and gzz = 2.0029 with the principal axis of gzz being 60° from the [001]* direction and gyy along the b-axis. A hyperfine (hf) structure due to the hf interaction between the electron spin and nuclear spins of two equivalent Ga atoms with a hf splitting of ∼29 G (for 69Ga) has been observed. The center can also be created by electron irradiation. Comparing the Ga hf constants determined by EPR with corresponding values calculated for different Ga vacancy-related defects, the IR1 defect is assigned to the double negative charge state of either the isolated Ga vacancy at the tetrahedral site (V2−Ga(I)) or the VGa(I)–Gaib–VGa(I) complex.
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Optically Driven Ultrafast Magnetic Order Transitions in Two-Dimensional Ferrimagnetic MXenes

Laser-induced switching of spins in materials is of great interest to revolutionize future magnetic storage technology and spintronics, which is generally realized in multicomponent ferrimagnetic (FiM) compounds but rare in 2D magnets. Using density functional theory (DFT) calculations, we show that 2D MXenes, including Cr2VC2F2, Mo2VC2F2, Mo2VN2F2, Mo3C2F2, and Mo3N2F2, have unusual FiM order. Interestingly, our real-time time-dependent DFT simulations demonstrate that laser pulses can directly induce ultrafast spin-selective charge transfer between magnetic sublattices in a few femtoseconds and further generate dramatic changes in the magnetic structure of these MXenes, including a transition from FiM to transient ferromagnetism (FM). The microscopic mechanism behind this ultrafast switching of spin is governed by the optically induced intersite spin transfer (OISTR) effect, which theoretically enables the ultrafast optical manipulation of the magnetic state in MXenes. Our results open new opportunities for exploring the optical manipulation of spin in 2D magnets.
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Optically Driven Ultrafast Magnetic Order Transitions in Two-Dimensional Ferrimagnetic MXenes

An adaptive design approach for defects distribution modeling in materials from first-principle calculations

Designing and understanding the mechanism of non-stoichiometric materials with enhanced properties is challenging, both experimentally and even computationally, due to the large number of chemical spaces and their distributions through the material. In the current work, it is proposed a Machine Learning approach coupled with the Efficient Global Optimization (EGO) method—an Adaptive Design (AD)—to model local defects in materials from first-principle calculations. Our method takes into account the smallest sample set as possible, envisioning the material defect structure relationship with target properties for new insights. As an example, the AD framework allows us to study the stability and the structure of the modified goethite (Fe0.875Al0.125OOH) by considering a proper defect distribution, from first-principle calculations. The chemical space search for the modified goethite was evaluated by starting from different sizes and configurations of the samples as well as different surrogate models (ANN and Gaussian Process; GP), acquisition functions, and descriptors. Our results show that the same local solution of several defect arrangements in Fe0.875Al0.125OOH is found regardless of the initial sample and regression model. This indicates the efficiency of our search method. We also discuss the role of the descriptors in the accelerated global search for defects in material modeling. We conclude that the AD method applied in material defects is a successful approach in automating the search within huge chemical spaces from first-principle calculations by considering small samples. This method can be applied to mechanistic elucidation of non-stoichiometric materials, solid solutions, alloys, and Schottky and Frenkel defects, essential for material design and discovery.
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An adaptive design approach for defects distribution modeling in materials from first-principle calculations

A Real-Time Time-Dependent Density Functional Tight-Binding Implementation for Semiclassical Excited State Electron–Nuclear Dynamics and Pump–Probe Spectroscopy Simulations

The increasing need to simulate the dynamics of photoexcited molecular systems and nanosystems in the subpicosecond regime demands new efficient tools able to describe the quantum nature of matter at a low computational cost. By combining the power of the approximate DFTB method with the semiclassical Ehrenfest method for nuclear–electron dynamics, we have achieved a real-time time-dependent DFTB (TD-DFTB) implementation that fits such requirements. In addition to enabling the study of nuclear motion effects in photoinduced charge transfer processes, our code adds novel features to the realm of static and time-resolved computational spectroscopies. In particular, the optical properties of periodic materials such as graphene nanoribbons or the use of corrections such as the “LDA+U” and “pseudo SIC” methods to improve the optical properties in some systems can now be handled at the TD-DFTB level. Moreover, the simulation of fully atomistic time-resolved transient absorption spectra and impulsive vibrational spectra can now be achieved within reasonable computing time, owing to the good performance of the implementation and a parallel simulation protocol. Its application to the study of UV/visible light-induced vibrational coherences in molecules is demonstrated and opens a new door into the mechanisms of nonequilibrium ultrafast phenomena in countless materials with relevant applications.
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A Real-Time Time-Dependent Density Functional Tight-Binding Implementation for Semiclassical Excited State Electron–Nuclear Dynamics and Pump–Probe Spectroscopy Simulations
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Contact

  • frauenheim@csrc.ac.cn
  • Level 6, Block 26, HongShan 6979 Phase Two, Longhua New District, ShenZhen, GuangDong 518000