2024
Richard Beckmann, Christoph Schran, Fabien Brieuc, Dominik Marx
Theoretical infrared spectroscopy of protonated methane isotopologues Journal Article
In: Phys. Chem. Chem. Phys., vol. 26, iss. 35, pp. 22846-22852, 2024.
Abstract | Links | BibTeX | Tags: Coupled Cluster, Quantum Dynamics, Spectra
@article{Beckmann2024/10.1039/D4CP02295E,
title = {Theoretical infrared spectroscopy of protonated methane isotopologues},
author = {Richard Beckmann and Christoph Schran and Fabien Brieuc and Dominik Marx},
url = {http://dx.doi.org/10.1039/D4CP02295E},
doi = {10.1039/D4CP02295E},
year = {2024},
date = {2024-08-13},
urldate = {2024-08-13},
journal = {Phys. Chem. Chem. Phys.},
volume = {26},
issue = {35},
pages = {22846-22852},
publisher = {The Royal Society of Chemistry},
abstract = {The vibrational spectroscopy of protonated methane and its mixed hydrogen/deuterium isotopologues remains a challenge to both experimental and computational spectroscopy due to the iconic floppiness of CH5+. Here, we compute the finite-temperature broadband infrared spectra of CH5+ and all its isotopologues, i.e. CHnD5−n+ up to CD5+, from path integral molecular dynamics in conjunction with interactions and dipoles computed consistently at CCSD(T) coupled cluster accuracy. The potential energy and dipole moment surfaces have been accurately represented in full dimensionality in terms of high-dimensional neural networks. The resulting computational efficiency allows us to establish CCSD(T) accuracy at the level of converged path integral simulations. For all six isotopologues, the computed broadband spectra compare very favorably to the available experimental broadband spectra obtained from laser induced reactions action vibrational spectroscopy. The current approach is found to consistently and significantly improve on previous calculations of these broadband vibrational spectra and defines the new cutting-edge for what has been dubbed the “enfant terrible” of molecular spectroscopy in view of its pronounced large-amplitude motion that involves all intramolecular degrees of freedom.},
keywords = {Coupled Cluster, Quantum Dynamics, Spectra},
pubstate = {published},
tppubtype = {article}
}
The vibrational spectroscopy of protonated methane and its mixed hydrogen/deuterium isotopologues remains a challenge to both experimental and computational spectroscopy due to the iconic floppiness of CH5+. Here, we compute the finite-temperature broadband infrared spectra of CH5+ and all its isotopologues, i.e. CHnD5−n+ up to CD5+, from path integral molecular dynamics in conjunction with interactions and dipoles computed consistently at CCSD(T) coupled cluster accuracy. The potential energy and dipole moment surfaces have been accurately represented in full dimensionality in terms of high-dimensional neural networks. The resulting computational efficiency allows us to establish CCSD(T) accuracy at the level of converged path integral simulations. For all six isotopologues, the computed broadband spectra compare very favorably to the available experimental broadband spectra obtained from laser induced reactions action vibrational spectroscopy. The current approach is found to consistently and significantly improve on previous calculations of these broadband vibrational spectra and defines the new cutting-edge for what has been dubbed the “enfant terrible” of molecular spectroscopy in view of its pronounced large-amplitude motion that involves all intramolecular degrees of freedom.
2022
Richard Beckmann, Fabien Brieuc, Christoph Schran, Dominik Marx
Infrared spectra at coupled cluster accuracy from neural network representations Journal Article
In: J. Chem. Theory Comput., 2022, ISSN: 1549-9618.
Abstract | Links | BibTeX | Tags: Coupled Cluster, Machine Learning Potentials, Spectra, Water
@article{Beckmann2022/10.1021/ACS.JCTC.2C00511,
title = {Infrared spectra at coupled cluster accuracy from neural network representations},
author = {Richard Beckmann and Fabien Brieuc and Christoph Schran and Dominik Marx},
doi = {10.1021/ACS.JCTC.2C00511},
issn = {1549-9618},
year = {2022},
date = {2022-08-01},
urldate = {2022-08-01},
journal = {J. Chem. Theory Comput.},
publisher = {American Chemical Society},
abstract = {Infrared spectroscopy is key to elucidate molecular structures, monitor reactions and observe conformational changes, while providing information on both structural and dynamical properties. This makes the accurate prediction of infrared spectra based on first-principle theories a highly desirable pursuit. Molecular dynamics simulations have proven to be a particularly powerful approach for this task, albeit requiring the computation of energies, forces and dipole moments for a large number of molecular configurations as a function of time. This explains why highly accurate first principles methods, such as coupled cluster theory, have so far been inapplicable for the prediction of fully anharmonic vibrational spectra of large systems at finite temperatures. Here, we push cutting-edge machine learning techniques forward by using neural network representations of energies, forces and in particular dipoles to predict such infrared spectra fully at "gold standard" coupled cluster accuracy as demonstrated for protonated water clusters as large as the protonated water hexamer, in its extended Zundel configuration. Furthermore, we show that this methodology can be used beyond the scope of the data considered during the development of the neural network models, allowing for the computation of finite-temperature infrared spectra of large systems inaccessible to explicit coupled cluster calculations. This substantially expands the hitherto existing limits of accuracy, speed and system size for theoretical spectroscopy and opens up a multitude of avenues for the prediction of vibrational spectra and the understanding of complex intra- and intermolecular couplings.},
keywords = {Coupled Cluster, Machine Learning Potentials, Spectra, Water},
pubstate = {published},
tppubtype = {article}
}
Infrared spectroscopy is key to elucidate molecular structures, monitor reactions and observe conformational changes, while providing information on both structural and dynamical properties. This makes the accurate prediction of infrared spectra based on first-principle theories a highly desirable pursuit. Molecular dynamics simulations have proven to be a particularly powerful approach for this task, albeit requiring the computation of energies, forces and dipole moments for a large number of molecular configurations as a function of time. This explains why highly accurate first principles methods, such as coupled cluster theory, have so far been inapplicable for the prediction of fully anharmonic vibrational spectra of large systems at finite temperatures. Here, we push cutting-edge machine learning techniques forward by using neural network representations of energies, forces and in particular dipoles to predict such infrared spectra fully at "gold standard" coupled cluster accuracy as demonstrated for protonated water clusters as large as the protonated water hexamer, in its extended Zundel configuration. Furthermore, we show that this methodology can be used beyond the scope of the data considered during the development of the neural network models, allowing for the computation of finite-temperature infrared spectra of large systems inaccessible to explicit coupled cluster calculations. This substantially expands the hitherto existing limits of accuracy, speed and system size for theoretical spectroscopy and opens up a multitude of avenues for the prediction of vibrational spectra and the understanding of complex intra- and intermolecular couplings.
Henrik R Larsson, Markus Schröder, Richard Beckmann, Fabien Brieuc, Christoph Schran, Dominik Marx, Oriol Vendrell
State-resolved infrared spectrum of the protonated water dimer: Revisiting the characteristic proton transfer doublet peak Journal Article
In: Chem. Sci., 2022, ISSN: 2041-6539.
Abstract | Links | BibTeX | Tags: Quantum Dynamics, Spectra, Water
@article{Larsson2022/10.1039/D2SC03189B,
title = {State-resolved infrared spectrum of the protonated water dimer: Revisiting the characteristic proton transfer doublet peak},
author = {Henrik R Larsson and Markus Schröder and Richard Beckmann and Fabien Brieuc and Christoph Schran and Dominik Marx and Oriol Vendrell},
doi = {10.1039/D2SC03189B},
issn = {2041-6539},
year = {2022},
date = {2022-08-01},
urldate = {2022-08-01},
journal = {Chem. Sci.},
publisher = {The Royal Society of Chemistry},
abstract = {The infrared (IR) spectra of protonated water clusters encode precise information on the dynamics and structure of the hydrated proton. However, the strong anharmonic coupling and quantum effects of these elusive species remain puzzling up to the present day. Here, we report unequivocal evidence that the interplay between the proton transfer and the water wagging motions in the protonated water dimer (Zundel ion) giving rise to the characteristic doublet peak is both more complex and more sensitive to subtle energetic changes than previously thought. In particular, hitherto overlooked low-intensity satellite peaks in the experimental spectrum are now unveiled and mechanistically assigned. Our findings rely on the comparison of IR spectra obtained using two highly accurate potential energy surfaces in conjunction with highly accurate state-resolved quantum simulations. We demonstrate that these high-accuracy simulations are important for providing definite assignments of the complex IR signals of fluxional molecules.},
keywords = {Quantum Dynamics, Spectra, Water},
pubstate = {published},
tppubtype = {article}
}
The infrared (IR) spectra of protonated water clusters encode precise information on the dynamics and structure of the hydrated proton. However, the strong anharmonic coupling and quantum effects of these elusive species remain puzzling up to the present day. Here, we report unequivocal evidence that the interplay between the proton transfer and the water wagging motions in the protonated water dimer (Zundel ion) giving rise to the characteristic doublet peak is both more complex and more sensitive to subtle energetic changes than previously thought. In particular, hitherto overlooked low-intensity satellite peaks in the experimental spectrum are now unveiled and mechanistically assigned. Our findings rely on the comparison of IR spectra obtained using two highly accurate potential energy surfaces in conjunction with highly accurate state-resolved quantum simulations. We demonstrate that these high-accuracy simulations are important for providing definite assignments of the complex IR signals of fluxional molecules.
2016
Maciej Śmiechowski, Christoph Schran, Harald Forbert, Dominik Marx
Correlated Particle Motion and THz Spectral Response of Supercritical Water Journal Article
In: Phys. Rev. Lett., vol. 116, no. 2, 2016, ISSN: 10797114.
Abstract | Links | BibTeX | Tags: Hydrogen bonding, Spectra, Water
@article{Smiechowski2016/10.1103/PhysRevLett.116.027801,
title = {Correlated Particle Motion and THz Spectral Response of Supercritical Water},
author = {Maciej Śmiechowski and Christoph Schran and Harald Forbert and Dominik Marx},
doi = {10.1103/PhysRevLett.116.027801},
issn = {10797114},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {Phys. Rev. Lett.},
volume = {116},
number = {2},
abstract = {Molecular dynamics simulations of supercritical water reveal distinctly different distance-dependent modulations of dipolar response and correlations in particle motion compared to ambient conditions. The strongly perturbed H-bond network of water at supercritical conditions allows for considerable translational and rotational freedom of individual molecules. These changes give rise to substantially different infrared spectra and vibrational density of states at THz frequencies for densities above and below the Widom line that separates percolating liquidlike and clustered gaslike supercritical water.},
keywords = {Hydrogen bonding, Spectra, Water},
pubstate = {published},
tppubtype = {article}
}
Molecular dynamics simulations of supercritical water reveal distinctly different distance-dependent modulations of dipolar response and correlations in particle motion compared to ambient conditions. The strongly perturbed H-bond network of water at supercritical conditions allows for considerable translational and rotational freedom of individual molecules. These changes give rise to substantially different infrared spectra and vibrational density of states at THz frequencies for densities above and below the Widom line that separates percolating liquidlike and clustered gaslike supercritical water.