# Research

A final draft of my Ph.D. thesis can be downloaded here: (11 Mb PDF):

*Understanding the Dielectric Properties of Water*

For publications, see also Google Scholar

## Journal articles

D. C. Elton, Z. Boukouvalas, M. S. Butrico, M. D. Fuge, and P. W. Chung, “Applying machine learning techniques to predict the properties of energetic materials” (arXiv:1801.04900), 2017

F. G. VanGessel, D. C. Elton, and P. W. Chung, “A Phonon Boltzmann Study of Microscale Thermal Transport in α-RDX Cook-Off”, 16th International Detonation Symposium, Cambridge MD, USA, July 2018. (abstract accepted)

D. C. Elton and M. Fritz, “Using a monomer potential energy surface to perform approximate path integral molecular dynamics simulation of ab-initio water at near-zero added cost” ((arXiv:1803.05740, in prep), 2018

My most recent project (currently unpublished but covered in the last chapter of my Ph.D. thesis), was on simulating water from “first principles”, ie. from the laws of quantum mechanics. The usual technique that physicists use to approximate the quantum mechanics of electrons in condensed matter systems, density functional theory, does not work well for water and much work is being done to understand its shortcomings. One usual assumption is that only electrons need to be treated quantum mechanically. We argue that for water both electrons and nuclei need to be treated quantum mechanically and that density functionals should be tested with nuclear quantum effects included. Our custom code implements a novel algorithm which greatly speeds up the calculation of nuclear quantum effects with only minor losses in accuracy. Accurate first principles simulations are important for developing energy materials and in computational drug design.

Elton, D.C. “The microscopic origin of the Debye relaxation in liquid water and fitting the high frequency excess response” *Phys. Chem. Chem. Phys.*, **19**, 18739 (2017) [arXiv]

We review the literature on the Debye absorption peak of liquid water and the excess response on the high frequency side, and find lack of agreement on the microscopic phenomena underlying both of these features. To better understand the molecular origin of Debye peak we ran and analyzed large scale molecular dynamics simulations. We introduce the “spectrumfitter” Python package for fitting dielectric spectra and analyze different ways of fitting the high frequency excess, and we propose using the generalized Lydanne-Sachs-Teller equation as a way of testing the physicality of model dielectric functions. Our results support the new theory by Popov, et al. that Debye relaxation is due to the propagation of defects through the H-bond network.

Elton, D. C. and Fernandez-Serra, M.-V. “The hydrogen bond network of water supports propagating optical phonon-like modes” *Nat. Comm.* **7**, 10913 (2016) [arXiv]

We show that on subpicosecond time scales optical phonon modes can propagate through the hydrogen bond network of water over relatively long distances (2-4 nm). For the first time we study the LO-TO splitting in water’s dielectric spectra and show how this splitting can be related to local structure. We point out a previously unnoticed discrepancy in the Raman spectra peak assignment and offer a solution.

Elton, D. C. and Fernandez-Serra, M.-V. “Polar nanoregions in water – a study of the dielectric properties of TIP4P/2005,TIP4P/2005f and TTM3F” *J. Chem. Phys.*, **140**, 124504 (2014) [arXiv]

We present a critical comparison of the dielectric properties of three types of water model used in molecular dynamics – rigid, flexible, and polarizable. To better understand the dielectric properties of water we make a novel analogy to the physics of polar nanoregions in relaxor ferroelectric materials. We argue that polarizability is essential to accurately reproducing the dipolar ordering of the liquid and how it changes with temperature.

J. J. Podesta, M. A. Forman, C. W. Smith, D. C. Elton, and Y. Malecot, “Accurate Estimation of Third-Order Moments from Turbulence Measurements“, *Nonlin. Proc. Geophys.,* **16,** 99 (2009) [arXiv.org]

## Science notes

feedback on these is always appreciated.

- Relation of crystal shape & structure to LO-TO splitting (2015)
- Elementary theory of solvation (2015)
- Energy Barriers and Rates – Transition State Theory for Physicists (2013)
- Stretched Exponential Relaxation (2013)
- Foundations of Quantum Mechanics & Quantum Computing (2012)
- Hydrogen bond network analysis for TIP4P water (2012)
- Maxwell’s equations in different conventions (2011)
- Some errata for
*Geometry, Topology, & Physics*by M. Nakahara (2011)