A5058852598- Advanced Chemical Physics Studies
- Spectroscopy and Quantum Chemical Studies
- Quantum, superfluid, helium dynamics
- Spectroscopy and Laser Applications
- Atmospheric Ozone and Climate
- Molecular Spectroscopy and Structure
- Laser-Matter Interactions and Applications
- Advanced NMR Techniques and Applications
- Quantum chaos and dynamical systems
- Molecular spectroscopy and chirality
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum many-body systems
- Quantum Mechanics and Non-Hermitian Physics
- Photochemistry and Electron Transfer Studies
- Electron Spin Resonance Studies
- Ammonia Synthesis and Nitrogen Reduction
- Mass Spectrometry Techniques and Applications
- Atmospheric chemistry and aerosols
- Quantum and electron transport phenomena
- Various Chemistry Research Topics
- Molecular Junctions and Nanostructures
- Physics of Superconductivity and Magnetism
- Cyclopropane Reaction Mechanisms
- Strong Light-Matter Interactions
- Magnetism in coordination complexes
Bielefeld University
2015-2024
SLAC National Accelerator Laboratory
2022
Pulse Biosciences (United States)
2022
Stanford University
2022
ORCID
2021
University of Gothenburg
2009
University of Iceland
2006-2009
Technical University of Munich
1998-2007
Haldor Topsoe (Denmark)
2006
University of Coimbra
2006
The multiconfigurational time-dependent Hartree (MCTDH) approximation to the Schrödinger equation is tested for a realistic three-dimensional example, photodissociation of NOCl. working equations MCTDH scheme introduced earlier are discussed in some detail. A computational presented which allows efficient numerical calculations. This applied NOCl after excitation S1 surface. results compared an exact wave-packet dynamics calculation. Fast convergence toward one found as number configurations...
The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional quantum dynamics calculations by representing the wavepacket in an optimal set of basis functions, called single-particle functions. Choosing these functions to be themselves wavefunctions which are represented using a MCTDH representation, multilayer scheme has been constructed and used for treating up 1000 degrees freedom rigorously [Wang Thoss, J. Chem. Phys. 199, 1289 (2003)]. present work gives...
A full-dimensional quantum dynamics simulation of a hydrogen atom reacting with methane on an accurate ab initio potential energy surface is reported. Based first-principles theory, thermal rate constants are predicted accuracy comparable to (or even exceeding) experimental precision. The theoretical prediction within the range significantly varied reported by different groups. This level has previously been achieved only for smaller, three-or four-atom reactive systems. Comparison classical...
Here, we give a full account of large collaborative effort toward an atomic-scale understanding modern industrial ammonia production over ruthenium catalysts. We show that overall rates can be determined by applying various levels theory (including transition state with or without tunneling corrections, and quantum dynamics) to range relevant elementary reaction steps, such as N(2) dissociation, H(2) hydrogenation the intermediate reactants. A complete kinetic model based on most steps...
The cumulative reaction probability (CRP) (the Boltzmann average of which is the thermal rate constant) has been calculated for H2+OH↔H2O+H in its full (six) dimensionality total angular momentum J=0. calculation, should be (numerically) exact result assumed potential energy surface, was carried out by a direct procedure that avoids having to solve complete state-to-state reactive scattering problem. Higher momenta (J≳0) were taken into account approximately obtain constant k(T) over range...
The nuclear dynamics on potential energy surfaces with a conical intersection is investigated the basis of exact (numerical) integration time-dependent Schrödinger equation. ethylene cation chosen as typical realistic model system. Complementing earlier work we study also in adiabatic basis, which will be seen to allow for more profound understanding decay and dephasing processes occurring computational effort exceeds considerably that propagation diabatic previous related studies have been...
The nuclear dynamics on potential energy surfaces which are strongly vibronically coupled through a conical intersection is investigated by exact (numerical) integration of the time-dependent Schrödinger equation. Results for realistic model systems including three degrees freedom presented: C2H+4, pyrazine and NO2. It was found previously C2H+4 that wave packet moves after an initial decay mainly lower adiabatic surface. This observation could be confirmed also By varying coupling strength...
Thermal rate constants are calculated for the H + CH(4) --> CH(3) H(2) reaction employing potential energy surface of Espinosa-Garcia (Espinosa-Garcia, J. Chem. Phys. 2002, 116, 10664). Two theoretical approaches used. First, we employ multiconfigurational time-dependent Hartree method combined with flux correlation functions. In this way in range 225-400 K obtained and compared previous results using same but Wu et al. (Wu, T.; Werner, H.-J.; Manthe, U. Science 2004, 306, 2227). It is found...
Accurate full-dimensional quantum mechanical calculations are reported for the CH4+H→CH3+H2 reaction employing Jordan–Gilbert potential energy surface. Benchmark results thermal rate constant and cumulative probability presented compared to classical transition state theory as well reduced dimensionality scattering calculations. The importance of effects in this system is highlighted.
A time-dependent discrete variable representation for evaluation of potential energy matrix elements in Hartree and multiconfiguration approaches is presented. In contrast to other representations, the scheme presented treats separable parts exactly not by quadrature. Thus, accurate results can be obtained even very small sizes grid. Time-dependent calculations photodissociation NOCl after S0→S1-excitation demonstrate accuracy this representation.
The multiconfigurational time-dependent Hartree (MCTDH) approach is applied to an example showing very complex dynamics: the wave-packet dynamics on three-dimensional B2 potential-energy surface of NO2. ability MCTDH scheme describe accurately severe splitting wave packet a saddle-shaped demonstrated. Internal checks calculation enable us assess degree convergence without need resort numerically exact calculation. As representative observable photodissociation spectrum calculated and...
Advances in the time propagation of multidimensional wave packets are exploited to present A-band photodissociation dynamics methyl iodide for five active vibrational modes on three relevant excited ab initio potential surfaces. The considered represent all experimentally observed dynamical activity. only neglected asymmetric C–H stretch and deformation group. kinetic energy operator corresponding these degrees freedom is derived. fully quantum mechanical calculation was implemented upon...
It is shown that the cumulative reaction probability for a chemical can be expressed (absolutely rigorously) as N(E)=∑kpk(E), where {pk} are eigenvalues of certain Hermitian matrix (or operator). The all lie between 0 and 1 thus have interpretation probabilities, eigenreaction probabilities which may thought rigorous generalization transmission coefficients various states activated complex in transition state theory. determined by diagonalizing directly available from Hamiltonian itself....
The cumulative reaction probability is calculated for the H2+OH→H+H2O in its full (six) dimensionality total angular momentum J=0. calculation, which should give (numerically) exact result assumed potential energy surface, yields directly, without having to solve complete state-to-state reactive scattering problem. Higher momenta (J≳0) were taken into account approximately obtain thermal rate constant k(T) over range 300°<T<700°. deviates significantly from experimental...
An improved approach for the direct calculation of thermal rate constants, employing multi-configurational time-dependent Hartree (MCTDH) and flux–flux correlation function, is presented. In this approach, flux operator diagonalized its eigenstates are propagated. The cumulative reaction probability obtained all energies simultaneously by a simple Fourier transform matrix elements between propagated eigenstates. Calculations H2+OH→H+H2O reaction, which include six internal degrees freedom...
The multiconfigurational time-dependent Hartree (MCTDH) approach facilitates multidimensional quantum dynamics calculations by employing a layered representation: in the upper layer of representation wave function is expanded basis single-particle functions, lower then these functions are represented larger time-independent basis. This two can be generalized to multilayer MCTDH further increase numerical efficiency. In recent work [U. Manthe, J. Chem. Phys. 128, 164116 (2008)], quadrature...
Benchmark calculations of the tunneling splitting in malonaldehyde using full dimensional potential proposed by Yagi et al. are reported. Two exact quantum dynamics methods used: multiconfigurational time-dependent Hartree (MCTDH) approach and diffusion Monte Carlo based projection operator imaginary time spectral evolution (POITSE) method. A ground state 25.7+/-0.3 cm(-1) is calculated POITSE. The MCTDH computation yields 25 converged to about 10% accuracy. These rigorous results used...
The multiconfigurational time-dependent Hartree (MCTDH) approach uses optimized sets of basis functions, called single-particle to represent multidimensional wavefunctions and thereby facilitates efficient quantum dynamics studies. function bases are usually for a single wavefunction. Here, an is studied which utilizes common several simultaneously, i.e., the constructed result in averaged description number wavefunctions. can favorably be used obtain eigenstates Hamiltonians or thermal...
Full-dimensional (multilayer) multi-configurational time-dependent Hartree calculations studying the intramolecular proton transfer in malonaldehyde based on a recent potential energy surface (PES) [Wang et al., J. Chem. Phys. 128, 224314 (2008)10.1063/1.2937732] are presented. The most accurate yield ground state tunneling splitting of 23.8 cm−1 and zero point 14 678 cm−1. Extensive convergence tests indicate an error margin quantum dynamics for about 0.2 These results to be compared with...
Full-dimensional quantum dynamics calculations for the H+CH(4)-->H(2)+CH(3) reaction using curvilinear coordinates are presented. A coordinate system to describe reactions of type X+YCH(3)-->XY+CH(3) is developed which facilitates efficient multiconfigurational time-dependent Hartree (MCTDH) approach. To bending motion X and Y atoms relative axis defined by CH(3) fragment, based on stereographic projection introduced. These yield a kinetic energy operator free singularities within...
State-to-state reaction probabilities for the H + CH4→ H2 CH3 are calculated by accurate full-dimensional quantum dynamics calculations employing multilayer multiconfigurational time-dependent Hartree approach and transition-state concept. Reactions starting from different vibrational rotational states of methane reactant investigated vanishing total angular momentum. The state distributions products found to be essentially independent initial rovibrational reactants. only show excitation in...
The mode-selective chemistry of the title reaction is studied by full-dimensional quantum dynamics simulation on an accurate ab initio potential energy surface for vanishing total angular momentum. Using a rigorous transition state based approach and multi-configurational time-dependent Hartree wave packet propagation, initial state-selected probabilities many ro-vibrational states methane are calculated. theoretical results compared with experimental trends seen in reactions methane. An...
An iterative block Lanczos-type diagonalization scheme utilizing the state-averaged multi-configurational time-dependent Hartree (MCTDH) approach is introduced. Combining propagation in real and imaginary time using a set of initial seed wavefunctions corresponding to excitations via different components dipole moment vector, can favorably be used selectively compute vibrational states which show high intensities absorption spectra. Tunneling splitted double well systems described...
Initial state-selected reaction probabilities of the H + CH4 → H2 CH3 are calculated in full and reduced dimensionality on a recent neural network potential [X. Xu, J. Chen, D. H. Zhang, Chin. Chem. Phys. 27, 373 (2014)]. The quantum dynamics calculation employs transition state concept multi-layer multi-configurational time-dependent Hartree approach rigorously studies for vanishing total angular momentum (J = 0). calculations investigate accuracy neutral study effect resulting from...