Flexible boundary layer using exchange for embedding theories. I. Theory and implementation

18 October 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Embedding theory is a powerful computational chemistry approach to exploring the electronic structure and dynamics of complex systems, with QM/MM being the prime example. A challenge arises when trying to apply embedding methodology to systems with diffusible particles, e.g. solvents, if some of them must be included in the QM region, for example in the description of solvent-supported electronic states or reactions involving proton transfer or charge-transfer-to-solvent: without a special treatment, inter-diffusion of QM and MM particles will lead eventually to a loss of QM/MM separation. We have developed a new method called Flexible Boundary Layer using Exchange (FlexiBLE) that solves the problem by adding a biasing potential to the system that closely maintains QM/MM separation. The method rigorously preserves ensemble averages by leveraging their invariance to exchange of identical particles. With a careful choice of the biasing potential, and the use of a tree algorithm to include only important QM and MM exchanges, we find the method has an MM-forcefield-like computational cost and thus adds negligible overhead to a QM/MM simulation. Furthermore, we show that molecular dynamics with the FlexiBLE bias conserves total energy and remarkably, dynamical quantities in the QM region are unaffected by the applied bias. FlexiBLE thus widens the range of chemistry that can be studied with embedding theory.

Keywords

QM/MM
solvated electron
molecular dynamics
water
solvation dynamics

Supplementary materials

Title
Description
Actions
Title
Supplementary Material
Description
Further details on our tree algorithm, the computational scaling of FlexiBLE, energy conservation for FIRES, a comparison of BEST with small versus large QM regions, BEST versus FlexiBLE energy conservation, energy conservation for FlexiBLE with a small bias exponent, dynamical properties from FlexiBLE with a large QM region, and structural properties from FlexiBLE with a double-exchange approximation.
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.