First-principle investigation of photophysical and photochemical reactions by means of non-adiabatic molecular dynamics

• Research unit: COST
• Project number: C09.0046

Key words (English)

Electronic structure; time-dependent density functional theory; first-principle excited state dynamics; non-adiabatic effects; nuclear quantum coherence and decoherence; femtosecond spectroscopy; electron transfer processes; molecular wires

Research programs (English)

COST-Action CM0702 - Chemistry With Ultrashort Pulses and Free-Electron Lasers: Looking for Control Strategies Through "Exact" Computations

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise: EPFL SB ISIC Laboratoire de chimie et biochimie comptuationelles BCH 4107 (Batochime UNIL)

Partners and International Organizations (English)

AT, BE, CH, DE, DK, ES, FI, FR, GR, HR, HU, IE, IT, NO, PL, RO, SE, UK

Abstract (English)

The principal aim of the project is to develop and implement methods for the study of non-adiabatic processes within the framework of density functional theory (DFT) and its time dependent extension, TDDFT, which are well suited for the study of medium to large size quantum systems. To this end, we planned to further develop the recently proposed TDDFT-based trajectory surface (TSH) molecular dynamics (MD) scheme, and to investgate possible possible alternative, more accurate solutions. The principal achievements can be summarized as follows: 1. Derivation of a rigorous nonadiabatic MD scheme (1,2] capable to go beyond the commonly used trajectory surface hopping approach based on the independent trajectory approximation. This method is derived ab-initio from the time-dependent Schrödinger equation for the combined electronnuclear wavefunction and it is based on the simultaneous propagation of a swarm of Bohmian trajectories that take into account all nuclear quantum effects. The implementation of this method is based on DFT/TDDFT for the calculation of all electronic properties such as PESs, forces, and nonadiabatic couplings. The method was applied to the study of simple molecular reactions in gas phase for which we obtained results in very good agreement with more expensive wave-packet propagation schemes. An extension of NABDY for the simulation of nonadiabatic effects in larger molecular systems is currently under investigation. 2. Development and implementation of a QM/MM scheme for the coupling of the TDDFT-based TSH excited state dynamics with a classically described MM environment [3]. A rigorous treatment of the solvent effects is crucial to the correct understanding of photochemical and photophysical processes occurring in solution. We showed that the knowledge of the solvent reorganization at atomistic scale resolution brings new fundamental insights into the mechanism of electron relaxation following photoexcitation [3]. 3. Derivation of a LR-TDDFT-based theory tor the calculation of non-adiabatic coupling vectors between excited states [4]. The efficient calculation of nonadiabatic coupling elements between excited states was one of the major limitation of all nonadiabatic mixed-quantum classical MD schemes. We have developed a new rigorous theoretical strategy tor the calculation of NACVs within LR-TDDFT, which can be applied to large molecular systems. 4. Implementation of a local control theory for laser pulse shaping within the LR-TDDFT-based TSH nonadiabatic dynamics [5]. This vew efficient scheme is a valid alternative to the computationally more involved optimal control scheme. The “optimal“ pulse is produced on-the-fly using a single TSH run, while in optimal control both forward and backward time propagations are required. 5. The methods described above have been applied to the study of the radiation induced defects formation in DNA base pairs in solution and in the design of improved dyes for dye-sensitized solar cells. Publications on both these subjects are planned for next year (2012).

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C09.0046