Browsing by Author "Metz, Michael P."
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Item Crystal Structure Predictions for 4-Amino-2,3,6-trinitrophenol Using a Tailor-Made First-Principles-Based Force Field(Crystal Growth and Design, 2022-01-24) Metz, Michael P.; Shahbaz, Muhammad; Song, Hongxing; Vogt-Maranto, Leslie; Tuckerman, Mark E.; Szalewicz, KrzysztofPredictions of crystal structures from first-principles electronic structure calculations and molecular simulations have been performed for an energetic molecule, 4-amino-2,3,6-trinitrophenol. This physics-based approach consists of a series of steps. First, a tailor-made two-body potential energy surface (PES) was constructed with recently developed software, autoPES, using symmetry-adapted perturbation theory based on a density-functional theory description of monomers [SAPT(DFT)]. The fitting procedure ensures asymptotic correctness of the PES by employing a rigorous asymptotic multipole expansion, which seamlessly integrates with SAPT(DFT) interaction energies. Next, crystal structure prediction (CSP) was performed by generating possible crystal structures with rigid molecules, minimizing these structures using the SAPT(DFT) force field, and running isothermal–isobaric molecular dynamics (MD) simulations with flexible molecules based on the tailor-made SAPT(DFT) intermolecular force field and a generic/SAPT(DFT) intramolecular one. This workflow led to the experimentally observed structure being identified as one of the forms with the lowest lattice energy, demonstrating the success of a first-principles, bottom-up approach to CSP. Importantly, we argue that the accuracy of the intermolecular potential, here the SAPT(DFT)-based potential, is determinative of the crystal structure, while generic/SAPT(DFT) force fields can be used to represent the intramolecular potential. This force field approach simplifies the CSP workflow, without significantly compromising the accuracy of the prediction.Item Fitted models for intermolecular interactions from first principles(University of Delaware, 2020) Metz, Michael P.Modern electronic structure methods are able to describe molecular systems accurately enough to predict most observed phenomena. Unfortunately, the compu- tational cost of such methods becomes prohibitively high as the size of the system grows. This problem can be alleviated by the use of relatively simple models which are fitted to data from high-level calculations. By maintaining the predictive accuracy of methods based on first principles at a computational cost which is many orders of magnitude smaller, these intermolecular potential energy surfaces (PESs) provide an important bridge to many applications in chemistry and materials science. Despite their importance and widespread use, these PESs are typically constructed in an ad hoc manner. The focus of this work is to generalize and improve upon existing method- ology for the generation of intermolecular PESs. These advancements are consolidated into a software package called autoPES, which is designed to be sufficiently automated that it is accessible to researchers with only a basic understanding of the underlying theory. The validity of this approach is demonstrated by applying it to predict the crystal structures of various organic molecules, and to compute accurate vibrational energies of the water, methane, and water-methane dimers. Finally, we extend the PES generation methodology to handle the difficult case where the monomers are allowed to deform substantially from their gas phase geometries.