Welcome to the ISPG, Antonio and Jack!

The ISPG welcomes two new members!

Dr. Antonio Prlj joined us as a Postdoctoral Researcher working on the excited-state dynamics of atmospheric molecules – financed by the ERC StG project SINDAM.

IMG_9279

Jack Taylor started a summer project in the group and will be working with Antonio on the calculation of photoabsorption cross-sections of transient volatile organic compounds.

IMG_1839

 

A series of new articles!

The ISPG just published a series of new articles.

excit-01

In collaboration with the group of Prof. Petr Slavíček in Prague, we investigated the role of initial conditions when simulating the excited-state dynamics of molecules. This question is particularly relevant if one is interested in the simulation of photoexcitation process triggered by long pulses, i.e., when the formation of a nuclear wavepacket in the excited state is not guaranteed. More information can be found in our article just accepted in Faraday Discussions.

More information in:
J. Suchan, D. Hollas, B. F. E. Curchod, P. Slavíček, On the Importance of Initial Conditions for Excited-State Dynamics, Faraday Discuss., accepted (2018).

The two following papers were published in a special issue of the European Journal of Physics B in honor of Hardy Gross.

cover_proposal_agostinicurchod

In the first article, we studied with Dr. Federica Agostini the dynamics of a nuclear wavepacket through a conical intersection using the formalism of the Exact Factorization (EF). In a previous work, we looked at a model of the photoisomerization of retinal for this purpose. In this new article, we employed a different model for the potential energy surfaces and played with their diabatic coupling to study how the time-dependent potential energy surface and vector potential – key quantities of the EF – behave in different nonadiabatic regimes.

More information in:
F. Agostini and B. F. E. Curchod, When the Exact Factorization Meets Conical Intersections…, Eur. Phys. J. B, 91, 141 (2018).

pop_coh_errorbars

In a second article, we studied the excited-state dynamics of oxirane using the method coined coupled-trajectory mixed quantum/classical (CT-MQC), combined with linear-response time-dependent density functional theory (LR-TDDFT). The results were compared with the Ab Initio Multiple Spawning strategy (also coupled to LR-TDDFT), which reproduces the branching of photoproducts observed in CT-MQC.

More information in:
B. F. E. Curchod
, F. Agostini, I. Tavernelli, CT-MQC – A Coupled-Trajectory Mixed Quantum/Classical method including nonadiabatic quantum coherence effectsEur. Phys. J. B, 91, 168 (2018).

Extended software development workshop in quantum dynamics

Basile was a co-organizer with Dr. Federica Agostini and Dr. Ari P. Seitsonen of the Extended Software Development Workshop (ESDW) in quantum dynamics, which took place in the “Maison de la Simulation” near Paris. Morning sessions were dedicated to the scientific presentations and HPC training, while coding sessions took place every afternoon. The central goal of this event was to further extend the E-CAM library of software for quantum dynamics, as well as to stimulate future developments in the field.

IMG_8654.jpg
Participants of the ESDW 2018.

More information about E-CAM software repositories can be found here.

 

How good are the approximations of Ab Initio Multiple Spawning?

Ab Initio Multiple Spawning (AIMS) is a method that allows for accurate yet efficient excited-state molecular dynamics. It portrays nuclear wavepackets as linear combinations of coupled Gaussian functions that follow classical trajectories. (See our recent review for a detailed discussion on this method.)

AIMS emerges from the (formally-exact) Full Multiple Spawning framework by invoking two central approximations related to the coupling between Gaussian functions. While AIMS has been successfully employed to simulate the photochemistry of numerous molecules, a detailed analysis of the strengths and weaknesses of its underlying approximations was missing in the literature.

Together with Dr. Benoît Mignolet (University of Liège), we investigated in great details the approximations in AIMS using a model molecule, LiH, photoexcited by an external electric field to generate interfering nuclear wavepackets. Interestingly, AIMS could capture the behavior of properties like electronic state populations and the more challenging time-dependent molecular dipole moment, even if this low-dimensional system constitutes one of the worst-case scenarios for the AIMS approximations. We furthermore proposed and validated strategies, compatible with the simulation of larger molecular systems, to overcome some potential shortcomings of these approximations.

(On a less serious note, this article is also the first one of the group fulfilling the requirements of the Palatinate Challenge.)

A walk through the approximations of ab initio multiple spawning, by Benoît Mignolet and Basile F. E. Curchod, J. Chem. Phys., 148, 134110 (2018).

fig1