title: Bond breaking in epoxy systems: A combined QM/MM approach.
abstract: A novel method to combine quantum mechanics (QM) and molecular mechanics has been developed to accurately and efficiently account for covalent bond breaking in polymer systems under high strain without the use of predetermined break locations. Use of this method will provide a better fundamental understanding of the mechano-chemical origins of fracture in thermosets. Since classical force fields cannot accurately account for bond breaking, and QM is too demanding to simulate large systems, a hybrid approach is required. In the method presented here, strain is applied to the system using a classical force field, and all bond lengths are monitored. When a bond is stretched past a threshold value, a zone surrounding the bond is used in a QM energy minimization to determine which, if any, bonds break. The QM results are then used to reconstitute the system to continue the classical simulation at progressively larger strain until another QM calculation is triggered. In this way, a QM calculation is only computed when and where needed, allowing for efficient simulations. A robust QM method for energy minimization has been determined, as well as appropriate values for the QM zone size and the threshold bond length. Compute times do not differ dramatically from classical molecular mechanical simulations.
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Ohio 45433, USA.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Barr
authors.affiliation: Engility Corporation, Air Force Research Laboratory, WPAFB, Ohio 45433, USA.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Kedziora
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Ohio 45433, USA.
authors.forename: Allison M
authors.initials: AM
authors.lastname: Ecker
authors.affiliation: Miami University, Oxford, Ohio 45056, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Moller
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Ohio 45433, USA.
authors.forename: Rajiv J
authors.initials: RJ
authors.lastname: Berry
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, Ohio 45433, USA.
authors.forename: Tim D
authors.initials: TD
authors.lastname: Breitzman