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Accurate characterization of charge-transfer excited states

Periodic Reporting for period 2 - AccuCT (Accurate characterization of charge-transfer excited states)

Reporting period: 2018-01-04 to 2019-01-03

Electronic charge transfer (CT) processes play an important role in photoactive molecules that have found great potential in solar energy conversion and environmental remediation.
A correct computational description of the electronic structure of CT excitations is essential for the bottom-up rational design of new photoactive molecules and materials.
These materials are of paramount importance for the 'development of a secure, clean and more efficient energy', one of the main focuses of the Horizon 2020 program.
The ideal computational method to study this kind of excitations should provide a quantitative description of state properties at low computational lost, making time-dependent
density functional theory (TDDFT) the method of choice. However, current TDDFT approximations fail to describe processes such as double excitations, Rydberg states, and particularly
CT excitations. The goal of this project was to develop a new family electronic structure methods for the quantitative description of CT excited states.
Upon completion of the project we have confirmed that excited-state methods based on self-interaction-error free methods are very good candidates for the
quantitative description of CT excited states. Accordingly, we have developed and implemented three new electronic structure methods, namely, Time-dependent Orbital-optimized
second-order perturbation theory (TD-OOMP2), Spin-flip Orbital-Optimized Orbital-optimized second-order perturbation theory (SF-OOMP2), and Time-dependent Orbital-Optimized
Double Hybrids (TD-OODH). The latter includes a mixture of local, and non-local exchange-correlation components. The proper ratio of these components can be achieved by means of
electron correlation measures. In this sense, we have proposed a new family of correlation indicators that are being used to improve hybrids methods.
The main results achieved during the reporting period are the development and implementation of three new electronic structure methods, namely, Time-dependent Orbital-optimized second-order perturbation theory (TD-OOMP2),
Spin-flip Orbital-Optimized Orbital-optimized second-order perturbation theory (SF-OOMP2), and Time-dependent Orbital-Optimized Double Hybrids (TD-OODH). These methods are able to describe properly excited states with strong
charge-transfer character. We have also proposed new indexes for electron correlation, that are currently been used to developed new electronic structure methods.

During the project I have participated disseminating the results of AccuCT at 10 international conferences where I have presented 2 invited talks, 4 oral communications, and 4 posters.
In addition, three open access papers have been published, one is currently under revision, and three more are currently in preparation. I also was invited to teach at two schools where I presented
the results of AccuCT to a broad audience of master, PhD students and postdocs. In addition, all the results related to the AccuCT project were posted on the website and social media of the researcher
(see https://eloyramoscordoba.wordpress.com/ or more details)
A correct computational description of the electronic structure of CT excitations, such as the one provided by using the methods developed in this project,
is essential for the bottom-up rational design of new photoactive molecules and materials. These materials are of paramount importance for the 'development
of a secure, clean and more efficient energy', one of the main focuses of the Horizon 2020 program.