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

The purpose of this school is to introduce its participants to state-of-the-art methodologies for the simulation of the dynamics of processes in the excited state, following the evolution in time of photoinitiated reactions, one of the priority topics of this call.

1.1.1. Motivation

The motivation of the school is to provide the attendants with the basic tools and knowledge to be able to simulate photoinduced processes, from conventional electronic spectroscopy to ultrafast laser-triggered phenomena, that could be applied to their own research. The approach to such simulations is carried out by ab initio strategies, including static calculations using multiconfigurational methods (electronic ab initio methods,) and dynamics simulations using different treatments for the nuclei, from full quantum dynamics to mixed quantum-classical dynamics.

These types of calculations are, on one hand, essential for characterizing excited states (ES), states that are involved in any photophysical and photochemical process initiated by light absorption in molecular systems, and its time evolution. The importance of such processes covers areas from biology/medicine to physical/material science and energy conversion. As an example, the interaction between UV light and DNA is the main 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 in such processes. Furthermore, the development of new nano-materials profiting of efficient and reversible photochemical reactions (photoswitches, microreactors) as well as the understanding of ultrafast (femto to attosecond) charge migration in ionized systems have grown exponentially in the last decades. As last case, ES are the basis of the sunlight conversion into energy, and the detailed understanding of such mechanism will enable the development of more efficient materials and technologies for clean energy production.

On the other, besides ES, other fundamental ground state processes as dissociation, ionization or triplet state formation (reactions that take place in the atmosphere and in the interstellar space), usually involves open-shell electronic states that require the use of this kind of computational methods. Furthermore, there are commonly several competing mechanisms and only a dynamic study can provide ratios estimations and timings for each of them.

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

1.1.2. Students

The school will be carried out in the frame of the Master in Theoretical Chemistry and Computational Modeling (TCCM) that has been recently supported by the Erasmus+ Programme of the European Union. This programme provides scholarships for worldwide students that will attend the school as training course during their first year of master studies after several intensive courses. Furthermore, the dissemination of the school is ensured due to its announcement in websites of the research groups and universities from the TCCCM consortium (https://www.emtccm.org/).

The school is also oriented and open to other postgraduate students in other areas such as atomic and molecular physics and in higher research levels (PhD students, postdocs or early-stage researchers) initiating in these types of computations. For this reason, we will also announce the school in two COST Actions, strongly related, and in which professors and research groups of the master are directly involved in their management and coordination: “Attosecond Chemistry” – AttoChem – CA18222, and “Molecular Dynamics in the GAS Phase – MDGAS – CA18212”)

Basics in quantum chemistry are only required as previous knowledge to attend the school since we provide also introductory lessons to photochemistry (see section 1.2; 1 block). In particular: Hartree-Fock Theory, Basis Sets, and basics on Configuration Interaction theory and Born-Oppenheimer approximation.

1.1.3. Goals

The final goal of the school is to provide the students with all the necessary tools and knowledge to understand and perform dynamic simulations for studying any process triggered by light absorption by a system. In order to achieve this target, first, a wide overview of the theoretical methods and tools, including those for static approaches, is delivered to the students. 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 process taking place after light absorption by a molecule: radiative (fluorescence, phosphorescence) and non-radiative (internal conversion, intersystem crossing, photochemistry…) and their competition. (section 1.2, 1 block)

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. (section 1.2, 2 block)

3. Set up and run dynamics simulations: pump-probe spectroscopy and non-adiabatic dynamics.  (section 1.2, 3 block)

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

These main objectives are achieved due 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 (section 1.2), which gradually build up the necessary knowledge, starting from the basics to eventually provide the students with state-of-the-art simulation methods for photochemistry. Six lessons provide the basis for the theoretical concepts that are settled and applied during 6 practical sessions (section 1.3) in which the students perform the simulations by their own guided at every moment by the teachers.