An Accurate Theoretical Prediction of the Zero Point Vibrational Energy of CH<sub>5</sub><sup>+</sup>

Kaledin, Alexey L.; Kunikeev, Sharif D.; Taylor, Howard S.

doi:10.1021/jp0486999

Cited by 12 publications

(22 citation statements)

References 29 publications

(25 reference statements)

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“…ϩ , recent semiclassical calculations of the zero-point energy by Kaledin et al 33 yield a value of 10 973 cm Ϫ1 , using the same surface, which is in excellent agreement with the value obtained by DMC.…”

Section: Dmc Resultssupporting

confidence: 80%

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Brown

McCoy

Braams

et al. 2004

The Journal of Chemical Physics

103

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We report a full dimensional, ab initio based potential energy surface for CH(5) (+). The ab initio electronic energies and gradients are obtained in direct-dynamics calculations using second-order Møller-Plesset perturbation theory with the correlation consistent polarized valence triple zeta basis. The potential energy and the dipole moment surfaces are fit using novel procedures that ensure the full permutational symmetry of the system. The fitted potential energy surface is tested by comparing it against additional electronic energy calculations and by comparing normal mode frequencies at the three lowest-lying stationary points obtained from the fit against ab initio ones. Well-converged diffusion Monte Carlo zero-point energies, rotational constants, and projections along the CH and HH bond lengths and the tunneling coordinates are presented and compared with the corresponding harmonic oscillator and standard classical molecular dynamics ones. The delocalization of the wave function is analyzed through comparison of the CH(5) (+) distributions with those obtained when all of the hydrogen atoms are replaced by (2)H and (3)H. The classical dipole correlation function is examined as a function of the total energy. This provides a further probe of the delocalization of CH(5) (+).

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Section: Dmc Resultssupporting

confidence: 80%

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Brown

McCoy

Braams

et al. 2004

The Journal of Chemical Physics

103

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“…95 The quantum-induced scrambling scenario has been confirmed much later by independent quantum Monte Carlo studies, 156,157,159 stressing the importance of anharmonic corrections to harmonic zero-point energy estimates. 158 Furthermore, it could be clearly shown, based on a thorough electronic structure analysis, that the three-center bonding character of the C rms structures is preserved within the constantly scrambling CH 5 + molecule, but again only in an average sense. 93 A major implication of these quantum simulations 92 is that the quantum motion of the five protons in three-dimensional space is not independent or completely random, despite the observed dramatic fluctuation effects, but rather ''correlated'' due to the particular chemical bonding pattern at work.…”

Section: F Computational Aspectsmentioning

confidence: 99%

Theoretical spectroscopy using molecular dynamics: theory and application to CH5+ and its isotopologues

Ivanov

Witt

Marx

2013

Phys. Chem. Chem. Phys.

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Infrared spectroscopy is a powerful technique to unravel the structure and dynamics of molecular systems of ever increasing complexity. For isolated molecules in the gas phase theoretical approaches that directly rely on solving the Schrödinger equation, either approximately or quasi-exactly, are well established. A distinctly different approach to compute infrared spectra can be based on advanced molecular dynamics, itself being based on classical Newtonian dynamics, in conjunction with concurrent first principles electronic structure calculations. At variance with traditional methods, which are formulated in terms of the Schrödinger representation of quantum mechanics, the molecular dynamics approach stems from Heisenberg's representation and thus relies on computing thermal expectation values of time-correlation functions. Crucial in addition to generating the spectra themselves is their decomposition in terms of modes, which can be assigned to correlated atomic motion. This ab initio molecular dynamics route to compute infrared spectra, and its recent extension to quasiclassical techniques relying on approximate path integral dynamics, is covered in the review part of this Perspective. The usefulness of this unconventional approach, which can be generalized beyond infrared spectroscopy, is demonstrated in detail by applying the full machinery in computing and assigning the infrared spectra of protonated methane and its isotopologues. This particular molecule is often considered to be the most prominent member of the class of floppy or fluxional molecules. CH5(+) has been a longstanding challenge for theoretical infrared spectroscopy because it undergoes intricate large-amplitude motion, which is also reviewed. Molecular dynamics based infrared spectroscopy is general and can be applied to diverse systems such as molecular complexes in the gas phase, chromophores in biomolecular environments, and solute-solvent systems in the liquid phase.

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“…Computationally, this requires at least methods such as centroid 86 or ring-polymer 87 molecular dynamics in the framework of ab initio path integral molecular dynamics 88 in order to improve the correlation functions in the spirit of our earlier analysis, 79 if not exact quantum dynamics 89,90 on global potential energy surfaces. [57][58][59]62 In the latter case, however, care must be taken to deal with excitations due to finite-temperature effects which were shown to affect the spectra beyond the ultracold regime. 69 It also remains to be seen what happens if the molecule is cooled down much below the current experimental temperature, 110 K, possibly using helium nanodroplets resulting in thermalization at about 0.4 K. Complementary to spectroscopy in frequency space would be the Coulomb explosion imaging technique 91 as a direct means to probe the real-space structures of molecular ions in the gas phase.…”

Section: Status Quo and Open Questionsmentioning

confidence: 99%

“…12 Contrary to early experiments, a host of theoretical investigations of five protons, one carbon nucleus and ten electrons has provided a wealth of insights. 12 In particular, structures and energetics, [54][55][56][57][58][59]61,62 (ro)vibrational spectra, [41][42][43][44][45][46][49][50][51]56,58,60 reactivity and chemical bonding, 28,30,36,43,52,55,62 and more recently also the dynamics, 9,48,49,53,[56][57][58][59]61,63 of this very small but utterly complicated molecule have been analyzed. Much of these studies revolved around the question what ''the structure'' of CH 5 1 is.…”

mentioning

confidence: 99%

“…9 The quantum-induced scrambling scenario has been confirmed much later by independent quantum Monte Carlo studies, 57,58,61 stressing the importance of anharmonic corrections to harmonic zero-point energy estimates. 59 Furthermore, it could be clearly shown, based on a thorough electronic structure analysis, that the three-center bonding character of the C s structures is preserved within the constantly scrambling CH 5 1 molecule, but again only in an average sense. 52 A major implication of these quantum simulations 48 is that the quantum motion of the five protons in three-dimensional space is not independent or completely random, despite the observed dramatic fluctuation effects, but rather ''correlated'' due to the particular chemical bonding pattern at work.…”

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confidence: 99%

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Understanding hydrogen scrambling and infrared spectrum of bare CH₅⁺based on ab initio simulations

Marx

2006

Phys. Chem. Chem. Phys.

112

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A comprehensive study of the properties of protonated methane obtained from ab initio molecular dynamics simulations is presented. Comparing computed infrared spectra to the measured one gives further support to the high fluxionality of bare CH(5)(+). The computational trick to partially freezing out large-amplitude motion, in particular hydrogen scrambling and internal rotation of the H(2) moiety, leads to an understanding of the measured IR spectrum despite the underlying rapid hydrogen scrambling motion that interconverts dynamically structures of different symmetry and chemical bonding pattern. In particular, the fact that C-H stretching modes involving the carbon nucleus and those protons that form the H(2) moiety and the CH(3) tripod, respectively, result in distinct peaks is arguably experimental support for three-center two-electron bonding being operative at experimental conditions. It is proposed that hydrogen scrambling is associated with the softening of a mode that involves the bending of the H(2) moiety relative to the CH(3) tripod, which characterizes the C(s) ground-state structure. The potential energy surface that is mapped on to a two dimensional subspace of internal coordinates provides insight into the dynamical mechanism for exchange of hydrogens between CH(3) tripod and the three-center bonded H(2) moiety that eventually leads to full hydrogen scrambling.

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An Accurate Theoretical Prediction of the Zero Point Vibrational Energy of CH₅⁺

Cited by 12 publications

References 29 publications

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Theoretical spectroscopy using molecular dynamics: theory and application to CH5+ and its isotopologues

Understanding hydrogen scrambling and infrared spectrum of bare CH₅⁺based on ab initio simulations

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An Accurate Theoretical Prediction of the Zero Point Vibrational Energy of CH5+

Cited by 12 publications

References 29 publications

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Quantum and classical studies of vibrational motion of CH5+ on a global potential energy surface obtained from a novel ab initio direct dynamics approach

Theoretical spectroscopy using molecular dynamics: theory and application to CH5+ and its isotopologues

Understanding hydrogen scrambling and infrared spectrum of bare CH5+based on ab initio simulations

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An Accurate Theoretical Prediction of the Zero Point Vibrational Energy of CH₅⁺

Understanding hydrogen scrambling and infrared spectrum of bare CH₅⁺based on ab initio simulations