Ab Initio Nonadiabatic Molecular Dynamics in Weakly Coupled Nanosystems.

Area of Science:

• Computational Chemistry and Materials Science
• Quantum Dynamics and Spectroscopy
• Nanoscale Science and Engineering

Background:

• Simulating excited-state processes in weakly coupled nanoscale systems, like layered materials, is challenging for traditional nonadiabatic molecular dynamics (NA MD).
• Standard NA MD methods struggle with divergent nonadiabatic coupling in such systems, limiting atomistic time-domain modeling.
• Two-dimensional (2D) perovskites show promise for optoelectronics but suffer from inefficient charge transport due to insulating organic spacers.

Purpose of the Study:

• To develop an efficient ab initio nonadiabatic molecular dynamics (NA MD) methodology for simulating excited-state dynamics in weakly coupled nanoscale systems.
• To implement decoherence-induced surface hopping (DISH) within a novel mixed diabatic-adiabatic representation (dNAMD) framework.
• To apply the DISH-dNAMD method to understand long-range charge transfer mechanisms in 2D perovskites and their impact on optoelectronic efficiency.

Main Methods:

• Developed a mixed diabatic-adiabatic representation (dNAMD) method that uses diabatization to handle weak inter-component coupling while retaining adiabatic representation within components.
• Integrated decoherence-induced surface hopping (DISH) into the dNAMD framework to enable accurate simulations of excited-state dynamics.
• Applied the DISH-dNAMD methodology to simulate long-range charge transfer in 2D perovskites with phenethylammonium and butylammonium spacers.

Main Results:

• The DISH-dNAMD method successfully simulated nano- to microsecond time-scale charge transfer in 2D perovskites, yielding results consistent with experimental data and Marcus theory.
• Simulations revealed that phenethylammonium spacers, due to increased rigidity, hydrogen bonding, and π-π stacking, significantly reduce electronic couplings and slow charge transfer rates (1-2 orders of magnitude) compared to flexible butylammonium spacers.
• Spacer rigidity was identified as a critical factor controlling interlayer charge transport in 2D perovskites, influencing electron-vibrational coupling and interlayer spacing.

Conclusions:

• The developed DISH-dNAMD framework offers an efficient and versatile tool for atomistic, time-domain simulation of excited-state dynamics in weakly coupled systems.
• Spacer engineering in 2D perovskites is crucial for controlling charge transport and enhancing optoelectronic device performance.
• The study advances the design principles for next-generation optoelectronic materials by elucidating the role of molecular structure in charge dynamics.