Vibrational Dynamics of the CH 4 ·F – Complex

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The low-resolution photodetachment spectrum of FCH(4)(-) is studied in full dimensionality employing the multi-configurational time-dependent Hartree approach and potential energy surfaces recently developed by Bowman and co-workers. The computed spectrum qualitatively agrees with the low-resolution spectrum measured by Neumark and co-workers. It displays two peaks which can be assigned to different vibrational states of methane in the quasi-bound F·CH(4) van der Waals complex. The first intense peak correlates to methane in its vibrational ground state while the second much smaller peak results from methane where one of the bending modes is excited. The present simulations consider only a single potential energy surface for the neutral FCH(4) system and thus do not include spectral contributions arising from transitions to excited electronic states correlating to the F((2)P) + CH(4) asymptote. Considering the quantitative differences between the computed and the experimental spectra, one cannot decide whether beside the vibrational excitation of the methane fragment also electronic excitation of FCH(4) contributes to the second peak in the experimental photodetachment spectrum.

Section: Wave Packet Propagationsupporting

confidence: 89%

“…For the anion, only small amplitude vibrations in a single potential well were considered (see Ref. 109 for a more detailed discussion of the localisation of the CH 4 F − complex). Therefore, the computations are less demanding.…”

Section: Wave Packet Propagationmentioning

confidence: 99%

A full-dimensional wave packet dynamics study of the photodetachment spectra of ${\rm FCH}_{4}^{-}$ FCH 4−

Palma

Manthe

2012

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“…Consequently, very long propagation times are required in the dynamical simulations. While detailed quantum mechanical calculations studying FCH 4 transition state spectra and low-lying pre-reaction complexes have been reported, 4,31,32,35,40 QD studies of reactive scattering have so far been restricted to low dimensionality studies of the F + CH 4 → HF + CH 3 reaction. 17,24,34 These calculations included a maximum of five coordinates and thus had to ignore important degrees of freedom.…”

mentioning

confidence: 99%

Communication: Mode specific quantum dynamics of the F + CHD3 → HF + CD3 reaction

Song

Yang

et al. 2016

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“…This is due to the difficulties encountered when evaluating matrix elements of the potential energy operator. The CDVR approach 35,36 has been successful in overcoming these difficulties 23,[37][38][39][40][41][42] , though its use requires an enormous amount of PES evaluations, which may require a large amount of computational resources. The alternative to CDVR is to represent (or fit) the PES in a form that is compatible with ML-MCTDH, in the sense that it allows efficient evaluation of the matrix elements.…”

Section: Discussionmentioning

confidence: 99%

Multi-layer Potfit: An accurate potential representation for efficient high-dimensional quantum dynamics

Otto

2014

The multi-layer multi-configuration time-dependent Hartree method (ML-MCTDH) is a highly efficient scheme for studying the dynamics of high-dimensional quantum systems. Its use is greatly facilitated if the Hamiltonian of the system possesses a particular structure through which the multi-dimensional matrix elements can be computed efficiently. In the field of quantum molecular dynamics, the effective interaction between the atoms is often described by potential energy surfaces (PES), and it is necessary to fit such PES into the desired structure. For high-dimensional systems, the current approaches for this fitting process either lead to fits that are too large to be practical, or their accuracy is difficult to predict and control.This article introduces multi-layer Potfit (MLPF), a novel fitting scheme that results in a PES representation in the hierarchical tensor (HT) format. The scheme is based on the hierarchical singular value decomposition, which can yield a near-optimal fit and give strict bounds for the obtained accuracy. Here, a recursive scheme for using the HT-format PES within ML-MCTDH is derived, and theoretical estimates as well as a computational example show that the use of MLPF can reduce the numerical effort for ML-MCTDH by orders of magnitude, compared to the traditionally used Potfit representation of the PES. Moreover, it is shown that MLPF is especially beneficial for high-accuracy PES representations, and it turns out that MLPF leads to computational savings already for comparatively small systems with just four modes.