Molecular enclosures appear broadly throughout many solid-state materials and biological systems alike, whether in nanoporous materials for energy storage or nanolipid particles for drug delivery. Importantly, the constituent ions and molecules that may be confined within these enclosures can largely determine the properties and performance of the system. It is critical to have a means of determining the density, relative concentration, arrangement, physical and electronic structure, viscosity, diffusivity, etc. of those constituents for two key reasons: a) the physics under such confinement can vary dramatically from bulk and remain poorly understood; and b) rational design of these enclosed systems is predicated on understanding how they are assembled. Current simulation methods fall short for accurately determining the density and structure of molecules packed inside small-scale enclosures, so there is a need for a new simulation method to address this technology gap.
LLNL researchers have developed a novel simulation methodology using slow growth thermodynamic integration (SGTI) utilizing spliced soft-core interaction potential (SSCP). The approach to filling the molecular enclosures is a nonphysical one. Rather than filling the pores from the open ends this method creates steps in the algorithm that allow molecules to pass through the pore wall and explore the internal volume and external volume equally at accelerated rates in order to make the positional, configurational, and rotational sampling more computationally economical.
Image Caption: Filled (8,8) (left) and (15,15) (right) CNTs with [EMIM+][BF4- ] using SGTI with the proposed spliced soft-core potential (SSCP) approach
![Filled (8,8) (left) and (15,15) (right) CNTs with [EMIM+][BF4- ] using SGTI with the proposed spliced soft-core potential (SSCP) approach](/sites/ipo/files/styles/scaled_300w/public/2025-09/Filled%20CNTs%20using%20SGTI.png?itok=ESwDWGIt)
Bernardi A, Meshot ER, Faller R. Confining Liquids inside Carbon Nanotubes: Accelerated Molecular Dynamics with Spliced, Soft-Core Potentials and Simulated Annealing. J Chem Theory Comput. 2020 Apr 14;16(4):2692-2702 (https://doi.org/10.1021/acs.jctc.0c00009)
Current stage of technology development: TRL 2
LLNL has patent(s) on this invention.
U.S. Patent No. 11734478 Spliced soft-core interaction potential for filling small-scale enclosures published 8/22/2023
- Better approximations of the wall thickness as the enclosure is being filled
- Shown to work on ionic liquids enclosed in carbon nanotubes (CNTs)
- Fully integrated with electrostatics, so it can work with charged species and electrified enclosures (e.g., electrode of a battery)
- Energy storage modeling of ion diffusion
- Drug development for understanding drug uptake through cellular membranes
- Ion diffusion through CNT membranes for water purification
