Computational benchmarking for ultrafast electron dynamics: wavefunction methods vs density functional theory

Attosecond electron dynamics in small- and medium-sized molecules, induced by an ultrashort strong optical pulse, is studied computationally for a frozen nuclear geometry. The importance of exchange and correlation effects on the nonequilibrium electron dynamics induced by the interaction of the molecule with the strong optical pulse is analyzed by comparing the solution of the time-dependent Schrodinger equation based on the correlated field-free stationary electronic states computed with the equation-of-motion coupled cluster singles and doubles and the complete active space multi-configurational self-consistent field methodologies on one hand, and various functionals in real-time time-dependent density functional theory (TD-DFT) on the other. We aim to evaluate the performance of the latter approach, which is very widely used for nonlinear absorption processes and whose computational cost has a more favorable scaling with the system size. We focus on LiH as a toy model for a nontrivial molecule and show that our conclusions carry over to larger molecules, exemplified by ABCU (C10H19N). The molecules are probed with IR and UV pulses whose intensities are not strong enough to significantly ionize the system. By comparing the evolution of the time-dependent field-free electronic dipole moment, as well as its Fourier power spectrum, we show that TD-DFT performs qualitatively well in most cases. Contrary to previous studies, we find almost no changes in the TD-DFT excitation energies when excited states are populated. Transitions between states of different symmetries are induced using pulses polarized in different directions. We observe that the performance of TD-DFT does not depend on the symmetry of the states involved in the transition.Belgian Fonds National de la Recherche Collective through project number 2.4545.12 “Control of attosecond dynamics: applications to molecular reactivity

Angle-Resolved Photoelectron Spectroscopy and Scanning Tunnelling Spectroscopy Studies of the Endohedral Fullerene Li@C60

M. S., E. B., J. O. F. T. and E. E. B. C. gratefully acknowledge financial support from the Leverhulme Foundation (RPF-298 “PES of hollow nanomaterials”). M. S. and H. J. C. acknowledge the financial support of EPSRC DTP studentships (EP/M508214/1 and EP/N509644/1). R. S. acknowledges financial support from the Scottish Funding Council through SRD-Grant (HRO7003). The work of FR and BM is supported by the Fonds de la Recherche Fondamentale Collective (#T.0132.16 and J.0012.18) and by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award # DE-SC0012628. BM and FR thank the Fonds National de la Recherche (FRS.FNRS, Belgium) for its support. Computational resources were provided by Consortium des équipements de calcul intensif (CECI, FNRS 2.5020.11).Gas phase photoelectron spectroscopy (Rydberg Fingerprint Spectroscopy), TDDFT calculations and low temperature STM studies are combined to provide detailed information on the properties of the diffuse, low-lying Rydberg-like SAMO states of isolated Li@C60 endohedral fullerenes. The presence of the encapsulated Li is shown by the calculations to produce a significant distortion of the lowest-lying S- and P-SAMOs that is dependent on the position of the Li inside the fullerene cage. Under the high temperature conditions of the gas phase experiments, the Li is mobile and able to access different positions within the cage. This is accounted for in the comparison with theory that shows a very good agreement of the photoelectron angular distributions, allowing the symmetry of the observed SAMO states to be identified. When adsorbed on a metal substrate at low temperature, a strong interaction between the low-lying SAMOs and the metal substrate moves these states to energies much closer to the Fermi energy compared to the situation for empty C60 while the Li remains frozen in an off-centre position.Publisher PDFPeer reviewe

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

Excited-State Molecular Dynamics Triggered by Light Pulses – Ab Initio Multiple Spawning vs Trajectory Surface Hopping

Trajectory surface hopping and ab initio multiple spawning are two commonly em ployed methods for simulating the excited-state dynamics of molecules. Trajectory surface hopping portrays the dynamics of nuclear wavepackets by a swarm of indepen dent classical trajectories, which can hop between electronic states. Ab initio multiple spawning, on the other hand, expresses nuclear wavepackets in a basis of traveling, coupled basis functions, whose number can be extended in case of coupling between electronic states. In the following, we propose to compare the performance of these two methods to describe processes involving the explicit interaction of a molecule with laser pulses. We base this comparison on the LiH molecule, as it is compatible with numerically-exact simulations using quantum dynamics. As recognized in earlier works, the limitations of TSH due to its inherent independent trajectory approximation are further enhanced when studying an explicit photoexcitation. While ab initio multiple spawning is also based on a series of approximations, the couplings between its trav eling basis functions allow for a proper description of phenomena that TSH cannot describe with its inherent independent trajectory approximation, even when applying decoherence corrections. We show here for different in silico experiments involving laser pulses that ab initio multiple spawning overcomes the limitations experienced by trajectory surface hopping and offers an at least qualitative description of population transfer between electronic states

Steering the outcome of a photochemical reaction - an in silico experiment on the H2CSO sulfine using few-femtosecond dump pulses

We propose a pump-dump control scheme using sub-10 fs pulses to enhance the photochemical formation of the three-membered C–S–O ring oxathiirane from the parent H2CSO sulfine molecule. The ultrashort nature of the pulses is essential to promptly alter the photoinduced dynamics, e.g., while a bond is elongating, which is key to selectively form the oxathiirane by radiative dumping. We carried out an in silico pump-dump experiment with excited-state dynamics simulations that include the interaction with electric field of the pump and dump pulses. By applying the dump pulse when the CS bond is elongating, the population transferred to the ground state will form the oxathiirane with a branching ratio of 4, much higher than the one solely due to nonradiative relaxation (0.66). The overall oxathiirane yield can be increased by up to 17% when the 6 fs IR dump pulse is applied at a delay time of 47 fs

A walk through the approximations of ab initio multiple spawning

Full multiple spawning offers an in principle exact framework for excited-state dynamics, where nuclear wavefunctions in different electronic states are represented by a set of coupled trajectory basis functions that follow classical trajectories. The couplings between trajectory basis functions can be approximated to treat molecular systems, leading to the ab initio multiple spawning method which has been successfully employed to study the photochemistry and photophysics of several molecules. However, a detailed investigation of its approximations and their consequences is currently missing in the literature. In this work, we simulate the explicit photoexcitation and subsequent excited-state dynamics of a simple system, LiH, and we analyze (i) the effect of the ab initio multiple spawning approximations on different observables and (ii) the convergence of the ab initio multiple spawning results towards numerically exact quantum dynamics upon a progressive relaxation of these approximations. We show that, despite the crude character of the approximations underlying ab initio multiple spawning for this low-dimensional system, the qualitative excited-state dynamics is adequately captured, and affordable corrections can further be applied to ameliorate the coupling between trajectory basis functions

Systèmes d'élevage et risque de pollution azotée. Construction d'un indicateur de risque et application dans la plaine des Vosges

National audienceA method for evaluating and localizing areas where there are risks of diffusing nitrates into the groundwater has been established and linked to the livestock farming system diversity and to their characteristic cropping plans. It has been applied to the 2211 farms present in 1993 in the Vosges plain. This method associates real nitrate leaching measures under farm fields, a livestock farm typology which contains information on the cropping plans, and a geographic information system to locate the information within water resource management units. Currently, the farm types combining big areas in cash crops and a maize forage system present the highest potential risks of nitrate pollution, while the farm types specialised in grassland dairy and/or meat production seem to be the least polluing. The farm type location makes it possible to identify geographic areas exposed to a high agricultural nitrate pollution risk, which are characterized by a combination of the most modernised and intensive farm types of the region.Une méthode d’évaluation et de localisation des risques de pollution nitrique diffuse des eaux souterraines, liés à la diversité des systèmes d’élevage de ruminants et à leurs assolements caractéristiques, est mise au point et appliquée sur les 2211 exploitations présentes en 1993 dans la plaine des Vosges. Cette méthode associe des mesures des lixiviations nitriques réelles sous des parcelles agricoles, une typologie des exploitations d’élevage qui contient des informations sur les assolements et un système d’information géographique qui permet de localiser les informations au sein d’unités territoriales de gestion des ressources en eau. Les exploitations combinant des surfaces importantes en grandes cultures et un système fourrager à base de maïs génèrent actuellement les plus forts risques de pollution par les nitrates, alors que les exploitations spécialisées dans les productions de lait et/ou de viande à base d’herbe apparaissent les moins polluantes. La localisation des types d’exploitation permet d’identifier des zones géographiques exposées à un fort risque de pollution d’origine agricole, caractérisées par une combinaison des types d’exploitation d’élevage les plus modernisés et intensifs de la région

Structure des films et enregistrement photographique direct en microscopie de champ (

Les auteurs discutent les possibilités qu’offre la microscopie de champ pour l’étude de la structure des films adsorbés.Par désorption de champ, on peut émettre des informationsa) sur le réseau des sites de désorption ;b) sur le réseau des sites utilisés en l’absence de champ et sur le mécanisme de la désorption.Pour recueillir ces informations, il faut une méthode de transmission et d’enregistrement très sensible. Les auteurs suggèrent l’enregistrement direct par impact des ions sur une plaque photographique située dans le microscope. Ils décrivent un appareil approprié à cet usage

Communication: XFAIMS—eXternal Field Ab Initio Multiple Spawning for electron-nuclear dynamics triggered by short laser pulses

Attoscience is an emerging field where attosecond pulses or few cycle IR pulses are used to pump and probe the correlated electron-nuclear motion of molecules. We present the trajectory-guided eXternal Field Ab Initio Multiple Spawning (XFAIMS) method that models such experiments “on-the-fly,” from laser pulse excitation to fragmentation or nonadiabatic relaxation to the ground electronic state. For the photoexcitation of the LiH molecule, we show that XFAIMS gives results in close agreement with numerically exact quantum dynamics simulations, both for atto- and femtosecond laser pulses. We then show the ability of XFAIMS to model the dynamics in polyatomic molecules by studying the effect of nuclear motion on the photoexcitation of a sulfine (H2CSO)