On-the-fly semiclassical study of internal conversion rates of formaldehyde

Ianconescu, Reuven; Tatchen, Jörg; Pollak, Eli

doi:10.1063/1.4825040

Cited by 29 publications

(28 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…31,37 Since the Hessians are not needed for the propagation of the classical trajectory, additional speed-up is achieved through parallel computation of the Hessians after the full trajectory is known. Note that other Hessian approximations, such as the Hessian update schemes [38][39][40] and Gaussian process regression 41,42 have been developed in the context of ab initio simulations. The considerable cost of multiple Hessian evaluations has also inspired various semiclassical approximations, 43 including the prefactor-free, 22 adiabatic, 44,45 harmonic, 43 and "poor person's" 46 variations of the Herman-Kluk propagator.…”

Section: Hessian Interpolationmentioning

confidence: 99%

Single-Hessian thawed Gaussian approximation

Begušić

Cordova

Vaníček

2019

The Journal of Chemical Physics

View full text Add to dashboard Cite

To alleviate the computational cost associated with on-the-fly ab initio semiclassical calculations of molecular spectra, we propose the single-Hessian thawed Gaussian approximation, in which the Hessian of the potential energy at all points along an anharmonic classical trajectory is approximated by a constant matrix. The spectra obtained with this approximation are compared with the exact quantum spectra of a one-dimensional Morse potential and with the experimental spectra of ammonia and quinquethiophene. In all cases, the single-Hessian version performs almost as well as the much more expensive on-the-fly ab initio thawed Gaussian approximation and significantly better than the global harmonic schemes. Remarkably, unlike the thawed Gaussian approximation, the proposed method conserves energy exactly, despite the time dependence of the corresponding effective Hamiltonian, and, in addition, can be mapped to a higher-dimensional time-independent classical Hamiltonian system.We also provide a detailed comparison with several related approximations used for accelerating prefactor calculations in semiclassical simulations.

show abstract

Section: Hessian Interpolationmentioning

confidence: 99%

Single-Hessian thawed Gaussian approximation

Begušić

Cordova

Vaníček

2019

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…57,58,62,65,66 Furthermore, they can be associated with ab initio direct dynamics with excellent results, 60,61,67−70 a key feature when dealing with molecules the size of glycine or larger. In fact, even if a large variety of very precise PES fitting techniques is available (see, for instance, refs (71−83). )…”

Section: Introductionmentioning

confidence: 99%

On-the-Fly ab Initio Semiclassical Calculation of Glycine Vibrational Spectrum

Gabas

Conte

Ceotto

2017

J. Chem. Theory Comput.

View full text Add to dashboard Cite

We present an on-the-fly ab initio semiclassical study of vibrational energy levels of glycine, calculated by Fourier transform of the wavepacket correlation function. It is based on a multiple coherent states approach integrated with monodromy matrix regularization for chaotic dynamics. All four lowest-energy glycine conformers are investigated by means of single-trajectory semiclassical spectra obtained upon classical evolution of on-the-fly trajectories with harmonic zero-point energy. For the most stable conformer I, direct dynamics trajectories are also run for each vibrational mode with energy equal to the first harmonic excitation. An analysis of trajectories evolved up to 50 000 atomic time units demonstrates that, in this time span, conformers II and III can be considered as isolated species, while conformers I and IV show a pretty facile interconversion. Therefore, previous perturbative studies based on the assumption of isolated conformers are often reliable but might be not completely appropriate in the case of conformer IV and conformer I for which interconversion occurs promptly.

show abstract

“…In contrast, the second term of Eq. (B3) vanishes within the rotating-wave approximation-its Fourier transform would lead to a spectrum at negative frequencies around −ω 21 . We recall now that the full expression for the spectrum [Eq.…”

Section: The First Term Of the Dipole Time Autocorrelation Function [mentioning

confidence: 99%

On-the-fly ab initio semiclassical evaluation of time-resolved electronic spectra

Begušić

Roulet

Vaníček

2018

The Journal of Chemical Physics

View full text Add to dashboard Cite

We present a methodology for computing vibrationally and time-resolved pump-probe spectra, which takes into account all vibrational degrees of freedom and is based on the combination of the thawed Gaussian approximation with on-the-fly ab initio evaluation of the electronic structure. The method is applied to the phenyl radical and compared with two more approximate approaches based on the global harmonic approximation-the global harmonic method expands both the ground-and excitedstate potential energy surfaces to the second order about the corresponding minima, while the combined global harmonic/on-the-fly method retains the on-the-fly scheme for the excited-state wavepacket propagation. We also compare the spectra by considering their means and widths, and show analytically how these measures are related to the properties of the semiclassical wavepacket. We find that the combined approach is better than the global harmonic one in describing the vibrational structure, while the global harmonic approximation estimates better the overall means and widths of the spectra due to a partial cancellation of errors.Although the full-dimensional onthe-fly ab initio result seems to reflect the dynamics of only one mode, we show, by performing exact quantum calculations, that this simple structure cannot be recovered using a one-dimensional model. Yet, the agreement between the quantum and semiclassical spectra in this simple, but anharmonic model lends additional support for the full-dimensional ab initio thawed Gaussian calculation of the phenyl radical spectra. We conclude that the thawed Gaussian approximation provides a viable alternative to the expensive or unfeasible exact quantum calculations in cases, where low-dimensional models are not sufficiently accurate to represent the full system.

show abstract

On-the-fly semiclassical study of internal conversion rates of formaldehyde

Cited by 29 publications

References 33 publications

Single-Hessian thawed Gaussian approximation

Single-Hessian thawed Gaussian approximation

On-the-Fly ab Initio Semiclassical Calculation of Glycine Vibrational Spectrum

On-the-fly ab initio semiclassical evaluation of time-resolved electronic spectra

Contact Info

Product

Resources

About