Non-adiabatic molecular dynamics simulation for carrier transport in a molecular monolayer

TL;DR

This paper introduces a novel non-adiabatic molecular dynamics method enabling efficient, accurate simulation of carrier transport in large organic monolayers, revealing new transport mechanisms and non-equilibrium behaviors.

Contribution

The authors develop a scalable simulation approach combining linear Hamiltonian approximation, charge patching, and fragment methods for large systems at DFT accuracy.

Findings

Discovered a new charge transfer mechanism involving state energy crossing.

Showed the system is not in thermodynamic equilibrium in terms of state populations.

Achieved large-scale simulations within hours using high-performance computing.

Abstract

We present a new approach to carry out non-adiabatic molecular dynamics to study the carrier mobility in an organic monolayer. This approach allows the calculation of a 4802 atom system for 825 fs in about three hours using 51,744 computer cores while maintaining a plane wave pseudopotential density functional theory level accuracy for the Hamiltonian. Our simulation on a pentathiophene butyric acid monolayer reveals a previously unknown new mechanism for the carrier transport in such systems: the hole wave functions are localized by thermo fluctuation induced disorder, while its transport is via charge transfer during state energy crossing. The simulation also shows that the system is not in thermo dynamic equilibrium in terms of adiabatic state populations according to Boltzmann distribution. Our simulation is achieved by introducing a linear time dependence approximation of the Hamiltonian within a fs time interval, and by using the charge patching method to yield the Hamiltonian, and overlapping fragment method to diagonalize the Hamiltonian matrix.