Charge Transfer Dynamics in Condensed Phase | Method Development and Materials Simulation Lab

Multistate charge transport in conductive metal-organic frameworks

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Conductive layered metal-organic frameworks (MOFs) are a new family of 2D materials which offer electrical conductivity in addition to permanent porosity and exceptionally high surface area. Owing to the ideal architecture and electrical properties of 2D MOFs, unprecedented breakthroughs are in horizon, in producing high-performance and cost-effective semiconductors; supercapacitors; and ion-to-electron transduced chemical sensors. In order to be able to decipher mechanistic details of charge transfer subject to a very flexible and dynamical framework, a deep atomistic level understanding of structural, electronic and dynamical behavior of 2D MOFs is required. Theoretical studies can be flag bearers in this quest and hence provide design guidelines for improving the charge mobility and turning these outstanding materials to practical devices for electrocatalysis, resistive sensing, and electrical energy storing.

**Developing ab initio parametrized force fields**

Dynamical flexibility is an intrinsic characteristics of 2D layered MOFs which should be investigated and addressed before any defect or dopant engineering strategy can be efficiently employed for tuning the electrical conductivity of these materials. Conducting such a study with ab initio molecular dynamics (AIMD) simulations, where the energies and forces felt by nuclei are calculated on-the-fly with an ab initio method, is very time consuming. Currently, typical time and length scales that are accessible with AIMD are up to hundreds of femtoseconds to tens of picoseconds, and up to a few hundreds of atoms. In response to this challenge, we develop ab initio parameterized force fields (AIFFs) specifically parametrized to reproduce the flexible dynamical structure of 2D MOFs. Using these AIFFs, we demonstrate a diverse range of interesting structural dynamics including (i) deformation of organic linkers, (ii) slipping of layers compared to each other, and (iii) constant expansion and contraction of layers along the stacking direction.

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Developing ab initio parametrized force fields

Moreover, we are able to study the behavior of water confined in different pores and channels of these porous materials where we characterize the mobility of water with respect to (i) diffusion in 1D channels, (ii) adsorption by forming either coordinative bonds with metal centers or formation of hydrogen bonds with organic linkers and, (iii) penetration within the interlayer spaces of these 2D -stacked layered materials.

Interfacing nonadiabatic dynamics methods and AIFFs

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To provide an accurate picture of the real time non-adiabatic dynamics of electron and hole polarons in conductive 2D MOFs specifically, and in porous materials in general, we are combining state-of-the-art MQCL and RPSH molecular dynamics approaches with potential energy surfaces (PESs) that are produced on-the-fly with the developed AIFFs in our research lab. Thus, we can investigate the electron-hole separation/recombination subject to constant dynamical deformations in these extremely flexible materials. A dynamic picture of electron-phonon coupling is currently being developed and the impact of the defect formations, creating trap states, on the rate of electron-hole recombination is under investigation.