Non-adiabatic effects in F + CHD3 reactive scattering

Palma J, Manthe U. Non-adiabatic effects in F + CHD3 reactive scattering. JOURNAL OF CHEMICAL PHYSICS. 2017;146(21): 214117.The effect of non-adiabatic transitions on the F(P-2) + CHD3(nu(1)) -> DF + CHD2 and F(P-2) + CHD3(nu(1)) -> HF + CD3 reactions is investigated. The dynamics of the nuclei was simulated using trajectory surface hopping and a vibronically and spin-orbit coupled diabatic potential energy matrix. To facilitate the calculations, the fewest switching algorithm of Tully was adapted to the use of a complex diabatic potential energy matrix. For reactions of CHD3 with ground state fluorine atoms, F(P-2(3/2)), the ratio between the previously computed adiabatic cross sections and the non-adiabatic ones was found to range from 1.4 to 2.1. The actual ratio depends on the translational energy and the initial vibrational state of CHD3. The total reactivity of CHD3(nu(1) = 1) was found to be always larger than that of CHD3(nu(1) = 0) mainly because of the increase in the cross sections for the HF + CD3 channel. Thus, the inclusion of non-adiabatic transitions in the theoretical treatment cannot resolve the existing disagreement between theory and experiment. Cross sections for the reaction of CHD3 with spin-orbit excited fluorine atoms, F(P-2(1/2)), were found to be significantly smaller than the ones for reaction with F(P-2(3/2)). Published by AIP Publishing

Quantum dynamics of H-2 in a carbon nanotube: Separation of time scales and resonance enhanced tunneling

Mondelo-Martell M, Huarte-Larranaga F, Manthe U. Quantum dynamics of H-2 in a carbon nanotube: Separation of time scales and resonance enhanced tunneling. JOURNAL OF CHEMICAL PHYSICS. 2017;147(8): 84103.Quantum confinement effects are known to affect the behavior of molecules adsorbed in nanostructured materials. In order to study these effects on the transport of a single molecule through a nanotube, we present a quantum dynamics study on the diffusion of H-2 in a narrow (8,0) carbon nanotube in the low pressure limit. Transmission coefficients for the elementary step of the transport process are calculated using the flux correlation function approach and diffusion rates are obtained using the single hopping model. The different time scales associated with the motion in the confined coordinates and the motion along the nanotube's axis are utilized to develop an efficient and numerically exact approach, in which a diabatic basis describing the fast motion in the confined coordinate is employed. Furthermore, an adiabatic approximation separating the dynamics of confined and unbound coordinates is studied. The results obtained within the adiabatic approximation agree almost perfectly with the numerically exact ones. The approaches allow us to accurately study the system's dynamics on the picosecond time scale and resolve resonance structures present in the transmission coefficients. Resonance enhanced tunneling is found to be the dominant transport mechanism at low energies. Comparison with results obtained using transition state theory shows that tunneling significantly increases the diffusion rate at T < 120 K. Published by AIP Publishing

The effect of surface relaxation on the N-2 dissociation rate on stepped Ru: A Transition State Theory Study

van Harrevelt R, Honkala K, Norskov JK, Manthe U. The effect of surface relaxation on the N2 dissociation rate on stepped Ru: A Transition State Theory Study. Journal of Chemical Physics. 2006;124(2):026102: 026102

The reaction rate for dissociative adsorption of N-2 on stepped Ru(0001): Six-dimensional quantum calculations

van Harrevelt R, Honkala K, Norskov JK, Manthe U. The reaction rate for dissociative adsorption of N2 on stepped Ru(0001): Six-dimensional quantum calculations. Journal of Chemical Physics. 2005;122(23): 234702.Quantum-mechanical calculations of the reaction rate for dissociative adsorption of N-2 on stepped Ru(0001) are presented. Converged six-dimensional quantum calculations for this heavy-atom reaction have been performed using the multiconfiguration time-dependent Hartree method. A potential-energy surface for the transition-state region is constructed from density-functional theory calculations using Shepard interpolation. The quantum results are in very good agreement with the results of the harmonic transition-state theory. In contrast to the findings of previous model calculations on similar systems, the tunneling effect is found to be small. (C) 2005 American Institute of Physics

A new time-dependent approach to the direct calculation of reaction rates

Manthe U. A new time-dependent approach to the direct calculation of reaction rates. JOURNAL OF CHEMICAL PHYSICS. 1995;102(23):9205-9213

Reaction Rates: Accurate quantum dynamical calculations for polyatomic systems

Manthe U. Reaction Rates: Accurate quantum dynamical calculations for polyatomic systems. J. Theo. Comp. Chem. 2002;1:153

A time-dependent discrete variable representation for (multiconfiguration) Hartree methods

Manthe U. A time-dependent discrete variable representation for (multiconfiguration) Hartree methods. JOURNAL OF CHEMICAL PHYSICS. 1996;105(16):6989-6994

On the integration of the multi-configurational time-dependent Hartree (MCTDH) equations of motion

Manthe U. On the integration of the multi-configurational time-dependent Hartree (MCTDH) equations of motion. Chemical Physics. 2006;329(1-3):168-178.The multi-configurational time-dependent Hartree approach facilitates multi-dimensional wave packet calculations studying polyatomic reaction processes. The efficiency of the approach results from the use of an optimally adapted time-dependent basis of single-particle functions employed in the wavefunction representation. As a consequence, the equations of motion are non-linear. An efficient integration scheme for these equations has been developed by Beck and Meyer [Z. Phys. D 42 (1997) 113]. The scheme is optimally suited for studies of systems where the Hamiltonian can be represented as a sum of products of single-particle operators. Employing the same basic ideas, the present work now introduces and discusses revised integration schemes which are more efficient for systems, where the Hamiltonian includes a general potential energy function. The H + CH4 H-2 + CH3 reaction is employed as an example to test the efficiency of the different schemes. (c) 2006 Elsevier B.V. All rights reserved