1,721,487 research outputs found
Semiclassical vibrational spectroscopy : the importance of quantum anharmonicity in supra-molecular systems
Full text linkSemiclassical (SC) vibrational spectroscopy has been applied successfully to several molecular systems thanks to the possibility to regain quantum effects accurately starting from short-time classical trajectories.[1-5] Larger molecular and supra-molecular systems represent instead an open challenge in the field of semiclassical spectroscopy mainly due to the necessity to work in very high dimensionality.
To start off the talk I will present some recent theoretical advances able to extend the range of applicability of SC vibrational spectroscopy to very high-dimensional systems.[6-7] Then, I will move to applications of semiclassical spectroscopy concerning the vibrational features of water clusters and two supra-molecular systems involving glycine.[8-9] These applications will point out the importance of a multi-reference, dynamical approach able to reproduce quantum anharmonicities without employing any ad-hoc scaling factor.
[1] M. F. Herman, E. Kluk, Chem. Phys. 1984, 91, 27.
[2] A. L. Kaledin, W. H. Miller, J. Chem. Phys. 2003, 118, 7174.
[3] M. Ceotto, S. Atahan, G. F. Tantardini, A. Aspuru-Guzik, J. Chem. Phys. 2009, 130, 234113.
[4] R. Conte, A. Aspuru-Guzik, M. Ceotto, J. Phys. Chem. Lett. 2013, 4, 3407.
[5] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2017, 13, 2378.
[6] M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett. 2017, 119, 010401.
[7] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 014307.
[8] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 104302.
[9] F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, to be submitted
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)
Semiclassical Molecular Dynamics for Spectroscopic Calculations of Complex Systems
Full text linkI will present some novel semiclassical methods for spectroscopic calculations. These approaches can be employed for spectroscopic calculations of gas-phase molecular and supramolecular systems
up to hundreds of degrees of freedom, as well as to condensed phase systems. Some methods are based on a “divide-and-conquer” approach, where the full dimensional spectra are obtained as a
composition of several lower dimensional ones. Others exploit hierarchically the different levels of accuracy of different semiclassical propagators. For instance, in a system-bath problem lower
semiclassical accuracy is dedicated to the bath, while the system is treated with higher accuracy and the system spectrum is eventually singled out.
All methods are amenable for ab initio molecular dynamics simulations.
References
1. F. Gabas, G. Di Liberto, R. Conte, and M. Ceotto, Chemical Science 9 (41), 7885-8026 (2018);
2. X. Ma, G. Di Liberto, R. Conte, W. L. Hase, and M. Ceotto, JCP 149, 164113 (2018)
3. M. Micciarelli, R. Conte, J. Suarez, and M. Ceotto, JCP 149, 064115 (2018);
4. M. Buchholz, F. Grossmann, and M. Ceotto, JCP 148, 114107 (2018);
5. G. Di Liberto, R. Conte, and M. Ceotto, JCP 148, 104302 (2018);
6. G. Di Liberto, R. Conte, and M. Ceotto, JCP 148, 014307 (2018);
7. M. Buchholz, F. Grossmann, and M. Ceotto, JCP 147, 164110 (2017);
8. M. Ceotto, G. Di Liberto, and R. Conte, PRL 119, 010401 (2017);
9. F. Gabas, R. Conte, and M. Ceotto, JCTC 13, 2378-2388 (2017);
10. G. Di Liberto, M. Ceotto, JCP 145, 144107 (2016);
11. M. Buchholz, F. Grossmann, M. Ceotto, JCP 144, 094102 (2016)
Quantum Mechanical Methods for Spectroscopic Calculations of High Dimensional Molecular Systems
Full text linkI will present some novel semiclassical methods for spectroscopic calculations. These approaches can be employed for spectroscopic calculations of gas-phase molecular and supramolecular systems
up to hundreds of degrees of freedom, as well as to condensed phase systems. Some methods are based on a “divide-and-conquer” approach, where the full dimensional spectra are obtained as a
composition of several lower dimensional ones. Others exploit hierarchically the different levels of accuracy of different semiclassical propagators.
All methods are amenable to ab initio molecular dynamics simulations.
References
1. M. Micciarelli, R. Conte, J. Suarez, and M. Ceotto, JCP 149, 064115 (2018);
2. M. Buchholz, F. Grossmann, and M. Ceotto, JCP 148, 114107 (2018);
3. G. Di Liberto, R. Conte, and M. Ceotto, JCP 148, 104302 (2018);
4. G. Di Liberto, R. Conte, and M. Ceotto, JCP 148, 014307 (2018);
5. M. Buchholz, F. Grossmann, and M. Ceotto, JCP 147, 164110 (2017);
6. M. Ceotto, G. Di Liberto, and R. Conte, PRL 119, 010401 (2017);
7. F. Gabas, R. Conte, and M. Ceotto, JCTC 13, 2378-2388 (2017);
8. G. Di Liberto, M. Ceotto, JCP 145, 144107 (2016);
9. M. Buchholz, F. Grossmann, M. Ceotto, JCP 144, 094102 (2016)
How many water molecules are needed to solvate one?
Full text linkThe comprehension at the molecular scale of the processes involved during solvation still remains a challenge in chemistry. Remarkably, the question concerning how many solvent molecules are necessary to solvate a solute one is still open. By exploring several water clusters of increasing size, we employ semiclassical spectroscopy [1-5] to determine on quantum dynamical grounds the minimal number of surrounding water molecules to make the central one display the same vibrational features of liquid water. We find out that the minimal structure eventually responsible of proper solvation is made of 21 water molecules, and that particular care must be reserved to the quantum description of the combination of the central monomer bending mode with network low-frequency librations.[6] The results obtained with the accurate ab initio potential are then compared with the popular Caldeira-Leggett one to rationalize whether a simplified model can qualitatively and quantitatively describe the solvated system behavior.[7] An ongoing study on how genetic algorithms[8] and adiabatically switched trajectories[9] can help to deconstruct the complex spectrum of the formic acid dimer will be also presented.
[1] E. J. Heller, Acc. Chem. Res. 14, 368-375 (1981).
[2] M. F. Herman and E. Kluk, Chem. Phys. 91, 27-34 (1984).
[3] A. L. Kaledin and W. H. Miller, J. Chem. Phys. 119, 3078-3084 (2003).
[4] M. Ceotto, S. Atahan, G. F. Tantardini and A. Aspuru-Guzik, J. Chem. Phys. 130, 234113 (2009).
[5] M. Ceotto, G. Di Liberto and R. Conte, Phys. Rev. Lett. 119, 010401 (2017).
[6] A. Rognoni, R. Conte and M. Ceotto, Chem. Sci. 12, 2060 (2021).
[7] A. Rognoni, R. Conte and M. Ceotto, J. Chem. Phys. 154, 094106 (2021). [8] M. Gandolfi, A. Rognoni, C. Aieta, R. Conte and M Ceotto, J. Chem. Phys. 153, 204104 (2020). [9] R. Conte, L. Parma, C. Aieta, A. Rognoni and M. Ceotto, J. Chem. Phys. 151, 214107 (2019)
“Divide-and-conquer” semiclassical molecular dynamics : An application to water clusters
Full text linkWe present an investigation of vibrational features in water clusters performed by means of our recently established divide-and-conquer semiclassical approach [M. Ceotto, G. Di Liberto, and R. Conte, Phys. Rev. Lett. 119, 010401 (2017)]. This technique allows us to simulate quantum vibrational spectra of high-dimensional systems starting from full-dimensional classical trajectories and projection of the semiclassical propagator onto a set of lower dimensional subspaces. The potential energy surface employed is a many-body representation up to three-body terms, in which monomers and two-body interactions are described by the high level Wang-Huang-Braams-Bowman (WHBB) water potential, while, for three-body interactions, calculations adopt a fast permutationally invariant ab initio surface at the same level of theory of the WHBB 3-body potential. Applications range from the water dimer up to the water decamer, a system made of 84 vibrational degrees of freedom. Results are generally in agreement with previous variational estimates in the literature. This is particularly true for the bending and the high-frequency stretching motions, while estimates of modes strongly influenced by hydrogen bonding are red shifted, in a few instances even substantially, as a consequence of the dynamical and global picture provided by the semiclassical approach
Building accurate and efficient ab initio potential energy surfaces for vibrational spectroscopy calculations via permutationally invariant polynomials
No full textI will start by briefly introducing the theory of permutationally invariant polynomials (PIPs) for the fitting of potential energy surfaces (PESs).[1] Then, I will focus on recent advances of the technique and related applications involving glycine, tropolone, and aspirin.[2-4] The Δ-machine learning approach and comparison of PIPs to other machine learning methods employed for PES construction will be discussed in detail.[5-7]
In the final part of the talk, after briefly introducing the basics of semiclassical vibrational spectroscopy,[8,9] I will present the outcome of such calculations for glycine and ethanol performed employing two PIP PESs.[2,10,11] Eventually, I will demonstrate the flexibility of semiclassical spectroscopy in dealing with large dimensional systems including solvated ones.[12,13]
The final goal is to demonstrate that efforts oriented to a more and more accurate and computationally affordable description of the electronic structure of complex and large dimensional systems may allow one to perform accurate spectroscopical (and other chemically significant) calculations.[14
"Divide and conquer" semiclassical molecular dynamics : A practical method for spectroscopic calculations of high dimensional molecular systems
Full text linkWe extensively describe our recently established "divide-and-conquer" semiclassical method [M. Ceotto, G. Di Liberto, and R. Conte, Phys. Rev. Lett. 119, 010401 (2017)] and propose a new implementation of it to increase the accuracy of results. The technique permits us to perform spectroscopic calculations of high-dimensional systems by dividing the full-dimensional problem into a set of smaller dimensional ones. The partition procedure, originally based on a dynamical analysis of the Hessian matrix, is here more rigorously achieved through a hierarchical subspace-separation criterion based on Liouville's theorem. Comparisons of calculated vibrational frequencies to exact quantum ones for a set of molecules including benzene show that the new implementation performs better than the original one and that, on average, the loss in accuracy with respect to full-dimensional semiclassical calculations is reduced to only 10 wavenumbers. Furthermore, by investigating the challenging Zundel cation, we also demonstrate that the "divide-and-conquer" approach allows us to deal with complex strongly anharmonic molecular systems. Overall the method very much helps the assignment and physical interpretation of experimental IR spectra by providing accurate vibrational fundamentals and overtones decomposed into reduced dimensionality spectra
Semiclassical Spectroscopy of Water Clusters Using High-Level Ab Initio Potentials
Full text linkI will start introducing state-of-art techniques in semiclassical dynamics that allow one to
undertake vibrational spectroscopy simulations involving many degrees of freedom and complex
molecules. An important class of such systems is represented by water clusters, which also
serve as prototypical examples of water (micro-)solvation. I will present some calculations on small water clusters (from the dimer through the decamer) to benchmark my semiclassical approach against MultiMode VCI estimates obtained by means of the ab initio WHBB potential energy surface, which I also adopted for the
semiclassical simulations. Then, I will show results of a semiclassical study aimed at determining the minimum
water cluster structure able to reproduce the spectroscopic features of liquid water including the
libration-bending combination band. For this study, involving a larger number of degrees of
freedom, I employed the accurate and faster-to-evaluate MB-Pol potential energy surface.
Finally, some remarks about possible developments on water cluster calculations will be
briefly illustrated
Full-Dimensional Ammonia Vibrational Spectrum from a Handful of Classical Trajectories
Full text linkThe accurate description of quantum properties in real molecules is a major computational task, due to the growing efforts required as the number of degrees of freedom of the system increases.
Different semiclassical methods have been adopted in the attempt to gather quantum properties from computationally cheap classical-trajectories simulations. However, issues related to possible chaotic behavior and classical integrator instability at long simulation times, together with large number of classical trajectories required often to limit the success of basic semiclassical approaches to model systems.
In the present work, we demonstrate that the multidimensional double well full vibrational spectrum, including tunnel splitting, can be described quite accurately by generating only 8 classical trajectories if Multi Coherent States Time Averaging SemiClassical Initial Value Representation (MC-TA-SCIVR) is used.[1-4] The first promising results have been obtained on a 1D double-well potential aimed at describing the umbrella motion in ammonia;[5] then, the full-dimensional vibrational spectrum of ammonia is presented, computed on both a high-level fitted PES [6,7] and ab-initio on-the-fly simulations.
For the first time in classical-trajectories based methods, both tunnel splitting amplitudes and quantum vibrational frequencies are simultaneously reported.[8,9] Moreover, the exiguous number of trajectories needed makes the present approach reliable for ab-initio on-the-fly approaches, thus avoiding the request for multidimensional PES calculations.[9]
References
[1] M. Ceotto, S. Atahan, G.F. Tantardini and A. Aspuru-Guzik, Multiple coherent states for first-principles semiclassical initial value
representation molecular dynamics, J. Chem. Phys. 130, 234113 (2009).
[2] M. Ceotto, S. Atahan, S. Shim, G.F. Tantardini and A. Aspuru-Guzik, First-principles initial value represenation molecular dynamics, PCCP 11, 3861 (2009).
[3] M. Ceotto, G.F. Tantardini and A. Aspuru-Guzik, Fighting the curse of dimensionality in first-principles semiclassical calculations: non-local reference states for large number of dimensions, J. Chem. Phys. 135, 214108 (2011).
[4] A.L. Kaledin and W.H. Miller, Time averaging the semiclassical initial value representation for the calculation of vibrational energy levels, J. Chem. Phys. 118, 7174 (2003).
[5] C.-K. Lin, H.-C. Chang and S.H. Lin, Symmetric Double-Well Potential Model and Its Application to Vibronic Spectra:Studies of
InversionModes of Ammonia and Nitrogen-Vacancy Defect Centers in Diamond, J. Phys. Chem. A 111, 9347 (2007).
[6] J.M.L. Martin and T.J. Lee, An Accurate ab Initio Quartic Force Field for Formaldehyde and Its Isotopomers, J. Mol. Spect. 160, 105
(1993).
[7] N.C. Handy, S. Carter and S.M. Colwell, The vibrational levels of ammonia, Mol. Phys. 96, 477 (1999).
[8] A.L. Kaledin and W.H. Miller, TA-SCIVR for vibrational levels. Application to H2CO, NH3, CH4, CH2D2, J. Chem. Phys. 119, 3078 (2003).
[9] R. Conte, A. Aspuru-Guzik and M. Ceotto, Full-dimensional ammonia vibrational spectrum from a handful of classical trajectories, in progress
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