“On the fly” QM/MM hybrid simulations of critical failure at the interface in CNT/polymer nanocomposites

Functionalised CNT/polymer composites are a class of strong, lightweight materials with application in many areas of technology, including aerospace. Developing a fundamental understanding of failure mechanisms at the CNT/polymer (CNP) interface can lead to making better materials suited to a broader range of applications.

From a computational perspective, the problem is challenging because it is multi-scale: the bond-breaking processes that occur at the CNP interface and initiate failure are inherently quantum mechanical (QM); yet the mechanisms by which external stresses are transferred through the polymer occur on length and time-scales far in excess of anything that can be simulated quantum mechanically.

We address this by using a QM/MM hybrid approach where classical molecular dynamics (MM) is used to simulate the majority of the system, while regions of particular interest are investigated using QM methods, utilising their accuracy and transferability. The QM regions are selected automatically “on the fly” [1] as the hybrid simulation proceeds. We use this to investigate critical failure at a CNP interface, showing that it leads to qualitatively different results compared to a fully classical, forcefield-based approach.

[1]Phys.Rev.Let.93(17):1-4,2004.