1,720,990 research outputs found
Semiclassical reaction rate constant calculations: investigation of anharmonicity and quantum effects
Full text linkSemiclassical transition state theory (SCTST) is a relatively simple method for the computation from first principles of reactive rate constants, including quantum effects while accounting for anharmonicity and the coupling between reactive and bound modes.[1-3] In this talk, I will illustrate how we have developed this technique for practical applications[4-7] involving the study of phenomena like kinetic isotope effects, heavy atom tunneling, and elusive conformer lifetimes.[5,6,8]
While many approximate reaction rate theories reduce to the parabolic barrier estimate for the tunneling correction at high temperatures, SCTST, which is based on vibrational perturbation theory (VPT2), gives the exact limit when one considers the leading order term in an expansion of powers of ħ2 of the tunneling transmission coefficient.[9-11] Our investigation of molecular reactive systems assesses the importance of the non-linear corrections to the parabolic barrier estimate of the transmission coefficient. When the reaction barrier is significantly anharmonic, it is mandatory to account for non-linear corrections; otherwise, the transmission coefficient overlooks a high-temperature regime which may be dominated by quantum reflection.[12] These results highlight the importance of having a theory such as SCTST that includes the correct high-temperature limit.
[1] W.H. Miller Faraday Discuss. Chem. Soc. 62, 40 (1977).
[2] W.H. Miller J. Chem. Phys. 62, 1899 (1975)
[3] R. Hernandez et al., Chem. Phys. Lett. 214, 129 (1993).
[4] C. Aieta, F. Gabas, M. Ceotto, J. Phys. Chem. A 120, 4853 (2016).
[5] C. Aieta F. Gabas, M. Ceotto, J. Chem. Theory Comput. 15, 2142 (2019).
[6] G. Mandelli, C. Aieta, M. Ceotto J. Chem. Theory Comput. 18, 623 (2022).
[7] J.R. Barker, MultiWell-2023 software suite; University of Michigan: Ann Arbor, Michigan, USA, 2023; http://clasp-research.engin.umich.edu/multiwell/
[8] G. Mandelli, L. Corneo, C. Aieta J. Phys. Chem. Lett. 14, 9996 (2023).
[9] E. Pollak, J. Cao, Phys. Rev. A, 107, 022203 (2023).
[10] E. Pollak, S Upadhyayula J. Chem. Phys. 160, (2024).
[11] E. Pollak J. Chem. Phys. 160, 150902 (2024).
[12] C. Aieta, M. Ceotto, E. Pollak, in preparation
A Time Averaged Semiclassical Approach to IR Spectroscopy
Full text linkSemiclassical vibrational spectroscopy is based on the evolution of classical trajectories and is able to reproduce quantum effects with good accuracy at the cost of a reasonable computational effort. [1-5] Nevertheless, semiclassical vibrational power spectra do not simulate all the features of the experimental IR spectra, since intensities in power spectra are not directly related to IR absorptions. Therefore, we
developed a new semiclassical approach to the calculation of molecular IR spectra by employing the time average technique upon symmetrization of the quantum dipole-dipole autocorrelation function. [6,7] We tested the accuracy of this new method on a few simple analytical systems and small molecules in the gas phase. In particular, spectra in the limit of infinite or zero temperature were investigated. Overall the method features excellent accuracy in calculating absorption intensities and provides estimates for the frequencies of vibrations in agreement with the corresponding power spectra.
[1] R. Conte, A. Aspuru-Guzik, and M. Ceotto, J. Phys. Chem. Lett. 4, 3407 (2013).
[2] G. Bertaina, G. Di Liberto, and M. Ceotto, J. Chem. Phys. 151, 114307 (2019).
[3] C. Aieta, M. Micciarelli, G. Bertaina, and M. Ceotto, Nat. Comm. 11, 4384 (2020).
[4] A. Rognoni, R. Conte, and M. Ceotto, Chem. Sci. 12, 2060 (2021).
[5] R. Conte, C. Aieta, G. Botti, M. Cazzaniga, M. Gandolfi, C. Lanzi, G. Mandelli, D. Moscato, and M. Ceotto, Theor. Chem. Acc. 142, 53 (2023).
[6] A. L. Kaledin and W. H. Miller, J. Chem. Phys. 118, 7174 (2003).
[7] A. L. Kaledin and W. H. Miller, J. Chem. Phys. 119, 3078 (2003)
Quantum nuclear densities from semiclassical on-the-fly molecular dynamics
No full textSemiclassical molecular dynamics is a rigorous approximation to quantum dynamics obtained from the exact quantum propagator expressed as Feynman’s path integral.[1] Recently, our group has introduced the Multiple Coherent Semiclassical Initial Value Representation (MC SCIVR) technique to reduce the number of classical trajectories required to converge vibrational spectra calculations from thousands to just a handful.[2-4] MC SCIVR has been applied successfully to several medium- and large-size molecular systems,[4-10] including fluxional and condensed phase ones.[11-13] In addition to the accurate anharmonic vibrational eigenvalue calculations, MC SCIVR yields vibrational eigenfunctions for both the ground and excited vibrational states.[14] In this talk, I will survey how we obtain the quantum anharmonic vibrational eigenfunctions from ab-initio on-the-fly trajectory simulations and how we extract the quantum nuclear densities and the geometry parameters probability distributions.[15,16] This information allows us to assign each peak in vibrational spectra, going beyond the usual harmonic normal-mode analysis. Our technique quantitatively determines how normal modes involving different functional groups cooperate to originate the spectroscopic signal. Furthermore, it allows for the visualization of the nuclear vibrations in a purely quantum picture, letting us both directly observe and quantify the effects of the full potential energy surface anharmonicity on the molecular structure. In particular, I will illustrate applications to the protonated glycine to reveal quantum mechanical and anharmonic vibrational features. The method will allow for a better rationalization of experimental spectroscopy.
[1] W.H. Miller, J. Phys. Chem. A 2001, 105, 2942.
[2] M. Ceotto, S. Atahan, S. Shim, G.F. Tantardini, A. Aspuru-Guzik, Phys. Chem. Chem. Phys. 2009, 11, 3861.
[3] M. Ceotto, S. Atahan, G.F. Tantardini, A. Aspuru-Guzik J. Chem. Phys. 2009, 130, 234113.
[4] R. Conte, M. Ceotto, In Quantum Chemistry and Dynamics of Excited States: Methods and Applications (eds L. González and R. Lindh) 2020.
[5] M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett. 2017, 119, 010401.
[6] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2017, 13, 2378.
[7] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 014307.
[8] F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, Chem. Sci. 2018, 9, 7894.
[9] F. Gabas, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 150, 224107.
[10] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2020, 16, 3476.
[11] G. Bertaina, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 151, 114307.
[12] A. Rognoni, R. Conte, M. Ceotto, Chem. Sci., 2021, 12, 2060.
[13] M. Cazzaniga, M. Micciarelli, F. Moriggi, A. Mahmoud, F. Gabas, and M. Ceotto, J. Chem. Phys. 2020, 152, 104104.
[14] M. Micciarelli, R. Conte, J. Suarez, M. Ceotto, J. Chem. Phys. 2018 149, 064115.
[15] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, Nat. Commun 2020, 11, 1.
[16] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, J. Chem. Phys., 2020, 153, 214117
Quantum nuclear densities from semiclassical on-the-fly molecular dynamics
No full textSemiclassical molecular dynamics is a rigorous approximation to quantum dynamics obtained from the exact quantum propagator expressed as Feynman’s path integral.[1] Recently, our group has introduced the Multiple Coherent Semiclassical Initial Value Representation (MC SCIVR) technique to reduce the number of classical trajectories required to converge vibrational spectra calculations from thousands to just a handful.[2-4] MC SCIVR has been applied successfully to several medium and large-size molecular systems,[4-10] including fluxional and condensed phase ones.[11-13] In addition to the accurate anharmonic vibrational eigenvalue calculations, MC SCIVR yields vibrational eigenfunctions for both the ground and excited vibrational states.[14] In this talk, I will survey how we obtain the quantum anharmonic vibrational eigenfunctions from ab-initio on-the-fly trajectory simulations and how we extract the quantum nuclear densities and the geometry parameters probability distributions.[15,16] This information allows us to assign each peak in vibrational spectra, going beyond the usual harmonic normal-mode analysis. Our technique quantitatively determines how normal modes involving different functional groups cooperate to originate the spectroscopic
signal. Furthermore, it allows for the visualization of the nuclear vibrations in a purely quantum picture, letting us both directly observe and quantify the effects of the full potential energy surface anharmonicity on the molecular structure. In particular, I will illustrate applications to the protonated glycine to reveal quantum mechanical and anharmonic vibrational features. The method will allow for a better rationalization of experimental spectroscopy.
[1] W.H. Miller, J. Phys. Chem. A 2001, 105, 2942.
[2] M. Ceotto, S. Atahan, S. Shim, G.F. Tantardini, A. Aspuru-Guzik, Phys. Chem. Chem. Phys. 2009, 11, 3861.
[3] M. Ceotto, S. Atahan, G.F. Tantardini, A. Aspuru-Guzik J. Chem. Phys. 2009, 130, 234113.
[4] R. Conte, M. Ceotto, In Quantum Chemistry and Dynamics of Excited States: Methods and Applications (eds L. González and R. Lindh) 2020.
[5] M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett. 2017, 119, 010401.
[6] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2017, 13, 2378.
[7] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 014307.
[8] F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, Chem. Sci. 2018, 9, 7894.
[9] F. Gabas, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 150, 224107.
[10] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2020, 16, 3476.
[11] G. Bertaina, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 151, 114307.
[12] A. Rognoni, R. Conte, M. Ceotto, Chem. Sci., 2021, 12, 2060.
[13] M. Cazzaniga, M. Micciarelli, F. Moriggi, A. Mahmoud, F. Gabas, and M. Ceotto, J. Chem. Phys. 2020, 152, 104104.
[14] M. Micciarelli, R. Conte, J. Suarez, M. Ceotto, J. Chem. Phys. 2018 149, 064115.
[15] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, Nat. Commun 2020, 11, 1.
[16] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, J. Chem. Phys., 2020, 153, 214117
Quantum and Semiclassical Methods for Molecular Rate Constants and Vibrational Spectra Calculations
No full textThis presentation reports about a quantum approximation for thermal rate constant calculations. The approximate rate expression is obtained from a stationary phase approximation to the time integral of the flux-flux correlation function. The resulting expression is shown to barely depend on the position of the flux operators, i.e. of the dividing surfaces. This property opens the route to applications to complex systems. We show how the approximation works on one and two dimensional systems with predominant quantum effects over a wide range of temperatures and the results are within few percent of the exact values, for a reasonable range of dividing surface positions.[1]
In a second part of the presentation, we show an optimized approach for the calculation of the vibrational density of states and the thermal rate constants in high-dimensional systems. We introduce a new code, called ParAdensum, which is based on the implementation of the Wang−Landau Monte Carlo algorithm for parallel architectures and part of the MULTIWELL suite.[2] We test the accuracy of ParAdensum on several molecular systems and show a significant computational speed-up with respect to standard approaches. The new code can easily handle 150 degrees of freedom.[3]
In a third part, a new semiclassical “divide-and-conquer” approach is presented. Here, the goal is to demonstrate that semiclassical dynamics simulations of high dimensional real molecular systems are doable. We first show the calculation of the quantum vibrational power spectra of small molecules for which benchmark quantum results are available, and we calculate the spectrum of C60, a system characterized by 174 vibrational degrees of freedom. The results show that quantum anharmonicities and purely quantum features like overtones are accurately accounted for, including when the molecular symmetry is broken and the degeneracy removed.[4]
References
[1] C. Aieta, M. Ceotto, submitted to J. Chem Phys. (under revision)
[2] J. R. Barker, et al. MultiWell Program Suite, Version 2014.1b; University of Michigan: Ann Arbor, MI, 2014; http://aoss-research.engin.umich.edu/multiwell/ (accessed June 25, 2014).
[3] C. Aieta, F. Gabas, and M. Ceotto, J. Phys. Chem. A 120, 4853 (2016)
[4] M. Ceotto, G. Di Liberto, and R. Conte, submitted to Phys. Rev. Lett. (under revision
Parallel Implementation of Semiclassical Transition State Theory and its application to high-dimensional tunneling reactions
Full text linkSemiclassical Transition State Theory (SCTST) can incorporate the non-separable coupling between degrees of freedom (DOFs) of reactive systems and include the effects of reaction path curvature and anharmonicity, as well as quantum tunneling contributions in the rate constant. The rate expression is derived by relying on a perturbative expansion for the vibrational energy which makes it possible to express the semiclassical cumulative reaction probability in a convenient way, without any further assumptions about the separability of the DOFs.[1-4]
The main goal of the talk is the extension of this semiclassical methodology to systems of increasing dimensionality upon computation of the densities of states for the reactants and the transition state by means of a convenient parallel implementation of the Wang-Landau algorithm.[5-6]
The new strategy is implemented into two codes, “paradensum” and “parsctst”, which are currently distributed with the open source MultiWell program suite for chemical kinetics.[7] The needed input information is just the reaction barrier height, the normal mode frequencies, and the anharmonic force constants, which are routinely calculated by suitable electronic structure packages.
After describing the codes and demonstrating their computational accuracy and efficiency, the new implementation is applied to estimate the rate constant of the proton transfer isomerization of the 2,4,6-tri-tert-butylphenyl to 3,5-di-tert-butylneophyl, a reaction involving 145 degrees of freedom and showing a clear tunneling regime below 250K.[6]
References
[1] Miller, W.H. J. Chem. Phys., 1975, 62, 1899 – 1906.
[2] Miller, W.H. Faraday Discuss. Chem. Soc. 1977, 62, 40 – 46.
[3] Miller, W.H.; Hernandez, R.; Handy, N.C.; Jayatilaka, D.; Willetts, A. Chem. Phys. Letters 1990, 172, 62 – 68.
[4] Hernandez, R.; Miller, W. H. Chem. Phys. Lett. 1993, 214 (2), 129 – 136.
[5] Aieta, C.; Gabas, F.; Ceotto, M. J. Phys. Chem. A 2016, 120 (27), 4853 – 4862.
[6] Aieta, C.; Gabas, F.; Ceotto, M. J. Chem. Theory Comput. 2019, 15, 2142 − 2153.
[7] Barker, J.R.; Nguyen, T.L.; Stanton, J.F.; Aieta, C.; Ceotto, M.; Gabas, F.; Kumar, T.J.D.; Li, C.G.L.; Lohr, L.L.; Maranzana, A.; Ortiz, N.F.; Preses, J.M.; Simmie, J.M.; Sonk, J.A.; Stimac, P.J.; MultiWell-2017 Software Suite; J.R. Barker, University of Michigan, Ann Arbor, Michigan, USA, 2019; http://clasp-research.engin.umich.edu/multiwell/
A quantum method for thermal rate constant calculations from stationary phase approximation of the thermal flux-flux correlation function integral
Full text linkThis paper presents a quantum mechanical approximation to the calculation of thermal rate constants. The rate is derived from a suitable stationary phase approximation to the time integral of the thermal flux-flux correlation function. The goal is to obtain an expression that barely depends on the position of the flux operators, i.e., of the dividing surfaces, so that it can be applied also to complex systems by arbitrarily locating the dividing surfaces. The approach is tested on one and two dimensional systems where quantum effects are predominant over a wide range of temperatures. The results are quite accurate, i.e., within a few percent of the exact values for a reasonable range of dividing surface positions
A Time Averaged Approach to IR Spectroscopy
Full text linkSemiclassical vibrational spectroscopy is based on the evolution of classical trajectories and is able to reproduce quantum effects with good accuracy at the cost of a reasonable computational effort. Nevertheless, semiclassical vibrational power spectra do not simulate all the features of the experimental IR spectra, since intensities in power spectra are not directly related to IR absorptions. Therefore, we developed a new semiclassical approach to the calculation of molecular IR spectra by employing the time average technique upon symmetrization of the quantum dipole-dipole autocorrelation function. We tested the accuracy of this new method on a few simple analytical systems and small molecules in the gas phase. Overall, the method features excellent accuracy in calculating absorption intensities and provides estimates for the frequencies of vibrations in agreement with the corresponding power spectra
Semiclassical vibrational spectroscopy from small molecules to solvated biomolecules
Full text linkThe hallmark of semiclassical dynamics is the ability to get quantum effects starting from classical
trajectories.[1] Therefore, the main challenge semiclassical methods have to face is to demonstrate
their accuracy and possibility to be applied even to large and complex systems.[2]
I will show that semiclassical dynamics can be straightforwardly interfaced to different descriptions
of the potential energy surface (PES), ranging from ab initio PESs[3-5] to force fields[6,7] and
QM/MM schemes. This allows one to apply semiclassical spectroscopy to the calculation of the
quantum vibrational features of very different systems, including not only small molecules
characterized by elusive Fermi resonances, like ethanol, or hard-to-assign experimental spectra, like
proline, but also large systems like solvated biomolecules. Finally, ongoing efforts to reproduce also
the intensity of absorption in the framework of semiclassical dynamics will be illustrated.[8]
[1] W. H. Miller The semiclassical initial value representation: A potentially practical way for
adding quantum effects to classical molecular dynamics J. Phys. Chem. A 105, 2942 (2001).
[2] M. Ceotto, G. Di Liberto, R. Conte Semiclassical “divide-and-conquer” method for
spectroscopic calculations of high dimensional molecular systems Phys. Rev. Lett. 119, 010401
(2017).
[3] R. Conte, A. Nandi, C. Qu, Q. Yu, P. L. Houston, and J. M. Bowman Semiclassical and
VSCF/VCI calculations of the vibrational energies of trans- and gauche-ethanol using a CCSD(T)
potential energy surface J. Phys. Chem. A 126, 7709 (2022).
[4] A. Rognoni, R. Conte, M. Ceotto Caldeira-Leggett model vs ab initio potential: A vibrational
spectroscopy test of water solvation J. Chem. Phys. 154, 094106 (2021).
[5] G. Botti, C. Aieta, R. Conte The complex vibrational spectrum of proline explained through the
adiabatically switched semiclassical initial value representation J. Chem. Phys. 156, 164303 (2022).
[6] F. Gabas, R. Conte, M. Ceotto Quantum vibrational spectroscopy of explicitly solvated
thymidine in semiclassical approximation J. Phys. Chem. Lett. 13, 1350 (2022).
[7] D. Moscato, F. Gabas, R. Conte, M. Ceotto Vibrational spectroscopy simulation of solvation
effects on a G-quadruplex J. Biomol. Struct. Dyn. doi:10.1080/07391102.2023.2180435 (2023).
[8] C. Lanzi, C. Aieta, M. Ceotto, R. Conte A semiclassical approach to IR spectroscopy, being
prepared
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