Photoinitiated processes are key for many relevant natural phenomena, and they also play an essential role in emerging fields, including renewable energy, material design, and nano-medicine. Traditionally, such excited state processes have been explained from a static point of view, delivering in some cases a biased, incorrect or incomplete description. Instead, the dynamic simulation, i.e. time evolution, of such processes is fundamental to understand chemical and physical mechanisms.

This school aims to introduce its participants to state-of-the-art methodologies for the simulation of excited state dynamics, following the evolution in time of photoinitiated reactions, which is one of the priority topics of this call. The school introduces tools to both efficiently and accurately model potential energy surfaces, as well as propagate the (quantum and semi-classical) nuclear dynamics relevant for a given photophysical or photochemical process.

Motivation

The school aims to provide the attendants with the basic tools and knowledge to simulate photoinduced processes, from conventional electronic spectroscopy to ultrafast laser-triggered phenomena, enabling the participants to apply these concepts to their own research interests. The school covers ab initio strategies, including static calculations using either time-dependent density functional theory or multiconfigurational methods, and dynamics simulations using different treatments for the nuclei, from full quantum dynamics to mixed quantum-classical dynamics.

On the one hand, these calculations are essential for characterizing excited states (ES), which are involved in any photophysical and photochemical process initiated by light in molecular systems, and its time evolution. The importance of such processes covers areas from biology/medicine to physical/material science and energy conversion. For example, the interaction between UV light and DNA is the primary source of direct DNA-photodamage but has also been applied in novel phototherapies against cancer and virus treatments. Thereby, the use of computational tools suited to treat ES and its time evolution in biologically relevant molecules provides a global picture that gives insights into such processes. Furthermore, the development of new nano-materials profiting from efficient and reversible photochemical reactions (photoswitches, microreactors) and the understanding of ultrafast (femto to attosecond) charge migration in ionized systems have grown exponentially in the last decades. Likewise, ES are the basis of the sunlight conversion into energy, and a detailed understanding of such a mechanism will enable the development of more efficient materials and technologies for clean energy production.

Besides ES, other fundamental ground state processes such as dissociation, ionization or triplet state formation (reactions in the atmosphere and in the interstellar space) usually involve open-shell electronic states that require the use of this kind of computational approach. Furthermore, photo-processes often feature several competing mechanisms, where dynamic studies can provide relative yields and their associated timings that help discern them.

At the end of the school, the students will be able to apply the acquired abilities to their research projects covering any of the subjects mentioned above and others related to electronic and vibrationally excited states in complex molecular systems.

Students

The school will be carried out in the frame of the Master in Theoretical Chemistry and Computational Modeling (TCCM) that is supported by the Erasmus+ Programme of the European Union. This programme provides scholarships for international students across the world that will attend the school as a training course during their first year of master’s studies after several intensive courses.

The school is also oriented and open to other postgraduate students in other areas such as atomic and molecular physics and higher research levels (PhD students, postdocs or early-stage researchers) initiating in these types of computations.

Only basics in quantum chemistry are required as previous knowledge to attend the school since we also provide introductory lessons to photochemistry. In particular, a background in Hartree-Fock Theory, One-electron Basis Sets, Configuration Interaction theory and the Born-Oppenheimer approximation is strongly desirable.

Goals

The final goal of the school is to provide students with all the necessary tools and knowledge to understand and perform dynamic simulations for studying any process triggered upon light absorption by a system. To achieve this target, a wide overview of the theoretical methods and tools is delivered to the students, including those for static approaches. In a subsequent step, those methods are applied to the dynamic simulations.

In short, the attendants at the end of the school would be able to:

1. Understand the main processes taking place after light absorption by a molecule: radiative (fluorescence, phosphorescence) and non-radiative (internal conversion, intersystem crossing, photochemistry…) decay and their competition.

2. Perform multiconfigurational (CASSCF/CASPT2) and TD-DFT calculations for excited states: simulation of vibrationally resolved electronic absorption spectra and characterization of potential energy surfaces.

3. Set up and run dynamics simulations: pump-probe spectroscopy and non-adiabatic dynamics.

4. Use several commercial and non-commercial computational packages and codes (OpenMolcas, FCclasses, Newton-X).

These main objectives are achieved thanks to the organization of the school, i.e. theoretical lessons delivered by internationally recognized experts in the field, complemented with computer sessions and designed in 3 interrelated blocks, which gradually introduce the necessary knowledge, starting from the basics to eventually provide the students with state-of-the-art simulation methods for photochemistry. Six sets of lectures (distributed over 3 different blocks and arranged in 10 sessions) are devised to provide the basis for the theoretical concepts that are applied during 5 practical sessions, in which the students perform the simulations on their own under the instructors’ guidance. Most practical sessions are interconnected, and the lecturers coordinate the specific contents to provide students with different perspectives to approach the very same systems.