QM/MM optimization with quantum coupling: Host-guest interactions in a pentacene-doped p-terphenyl crystal

In this work, we present a novel force-based scheme to perform hybrid quantum mechanics/molecular mechanics (QM/MM) computations. The proposed scheme becomes especially relevant for the simulation of host-guest molecular systems, where the description of the explicit electronic interactions between a guest molecule and a classically described host is of key importance. To illustrate its advantages, we utilize the presented scheme in the geometry optimization of a technologically important host-guest molecular system: a pentacene-doped p-terphenyl crystal, a core component of a room-temperature MASER device. We show that, as opposed to the simpler and widely used hybrid scheme ONIOM, our Quantum-Coupling QM/MM scheme was able to reproduce explicit interactions in the minimum energy configuration for the host-guest complex. We also show that, as a result of these explicit interactions, the host-guest complex exhibits an oriented net electric dipole moment that is responsible for red-shifting the energy of the first singlet-singlet electronic excitation of pentacene. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

In this work, a novel force-based scheme for hybrid quantum mechanics/molecular mechanics (QM/MM) computations is presented. The scheme is particularly relevant for simulating host-guest molecular systems and accurately describing the explicit electronic interactions between a guest molecule and a classically described host. By applying the scheme to the optimization of a technologically important host-guest molecular system, a pentacene-doped p-terphenyl crystal, it is shown that the proposed Quantum-Coupling QM/MM scheme can reproduce explicit interactions in the minimum energy configuration for the host-guest complex. Furthermore, it is demonstrated that these explicit interactions result in an oriented net electric dipole moment in the host-guest complex, which is responsible for red-shifting the energy of the first singlet-singlet electronic excitation of pentacene.