The awards go to Tel Aviv University’s Barak Hirshberg and Princeton University’s Marissa Weichman for their work in observing, understanding, and quantifying molecular dynamics
MELVILLE, N.Y., Sept. 6, 2024 — The Journal of Chemical Physics (JCP) is honored to announce Profs. Barak Hirshberg and Marissa Weichman as the 2023 winners of the JCP Best Paper by an Emerging Investigator Award.
Profs. Hirshberg and Weichman will receive a $2,000 honorarium and are invited to write a perspective article for JCP. They were selected from a pool of papers in the 2023 JCP Emerging Investigators Special Collection by a committee composed of Editorial Advisory Board Members. The special collection is intended to be a recognition of excellence in itself, as it has a higher standard for acceptance than the journal.
Submissions for the 2024 JCP Emerging Investigators Special Collection are now open. To qualify for the award, the principal investigator must be within 10 years of their graduate degree graduation date.
Barak Hirshberg
Prof. Hirshberg, senior lecturer at Tel Aviv University’s School of Chemistry, was recognized for his paper, “Quadratic scaling bosonic path integral molecular dynamics,” published in JCP on Oct. 19, 2023.
According to Hirshberg, molecular dynamics (MD) simulations provide you with a “virtual microscope” through which you can track the motion of every atom in a wide array of systems. While this offers invaluable insight into chemical and physical processes, there are two limitations: First, they are inherently classical, and standard algorithms neglect quantum effects entirely; and second, they are limited in timescale because the propagation uses intervals smaller than the system’s fasted vibrations.
To solve the first problem, Prof. Hirshberg’s team has put together computationally scalable algorithms that factor fermionic and bosonic exchange effects — which are responsible for a variety of quantum phenomena — into their classical MD simulations. These efforts were exemplified by the team’s winning paper.
“In this paper, Prof. Hirshberg reports a new algorithm for efficiently simulating path integral molecular dynamics of systems consisting of a large number of bosons,” said JCP Editor-in-Chief Dr. Tim Lian. “This development provides a much-needed new method for simulating quantum nuclear effects in large bosonic systems that are of interest to many potential applications, including quantum materials.”
Building on postdoctoral work in which he was part of a team that determined a way to reduce computational scaling from exponential to cubic through recursive evaluation of ring polymer forces, Prof. Hirshberg and Schmidt Science Fellow Dr. Yotam Feldman established a method relying on quadratic scaling — speeding things up in orders of magnitude and allowing for path integral MD simulations of thousands of bosonic quantum particles for the first time.
“As a scientist, the highest reward is to see that our community appreciates our work,” said Prof. Hirshberg. “The Journal of Chemical Physics is my scientific home. I send some of my best papers there, knowing they will go through a professional, helpful, and fast peer-review process.”
He went on to note that he’s “thrilled” this particular paper won because it represents interdisciplinary efforts performed alongside Dr. Feldman, who specialized in computer science before moving over to theoretical chemical physics.
“This sort of interdisciplinary work is not always appreciated, but in JCP, it was — for which we are incredibly thankful,” said Prof. Hirshberg.
A graduate of the Hebrew University of Jerusalem’s Amirim Natural Sciences Honors Program as well as a former Adams Fellow at the Israel Academy of Sciences and Humanities and Rothschild Postdoctoral Fellow at ETH Zurich, Prof. Hirshberg credits Profs. R. Benny Gerber and Michele Parrinello with guiding and inspiring him in the earliest portions of his career. He joined the faculty at Tel Aviv University’s School of Chemistry in January 2021.
“I am thankful for my department, which provides a supportive and intellectually stimulating environment for me to pursue my science dreams, and my group members, who are intelligent, motivated, and fun to work with,” said Prof. Hirshberg.
With regard to his plans for his current or future work, Prof. Hirshberg noted he’d like to go a step further past evaluating thermal averages for bosonic condensed phases, instead obtaining their dynamic transport properties — a significant challenge, he noted, because simulations converge exponentially slowly as a result of the dynamical sign problem.
He’d also like to tackle the evaluation of thermal expectation values of large fermionic systems, which themselves prove exponentially slow to converge at low temperatures or large numbers because of the fermionic sign problem.
“Both issues probably could not be solved exactly, but even making a dent in them, extending the range of timescales and systems we could simulate, would be a great achievement,” said Prof. Hirshberg.
Marissa Weichman
Prof. Weichman, assistant professor of chemistry at Princeton University’s Department of Chemistry, was recognized for her paper, “Ultrafast dynamics of CN radical reactions with chloroform solvent under vibrational strong coupling,” published in JCP on Oct. 23, 2023.
According to Prof. Weichman, while more and more research has demonstrated strong light-matter coupling between a molecular vibrational mode and the confined electromagnetic field of an optical cavity can alter chemical reactivity, the underlying mechanisms behind cavity-altered chemistry are still something of a mystery because the reaction dynamics of the systems involved have proven too complex to understand.
In the award-winning paper, Prof. Weichman’s team utilized ultrafast spectroscopy to watch in real time as cyanide (CN) radicals reacted with strongly cavity-coupled chloroform (CHCl3) solvent molecules. The team found vibrational strong coupling does not significantly alter any measured rate constants — including those associated with hydrogen abstraction.
It is, to Prof. Weichman and her team’s knowledge, the first experimental study of an elementary biomolecular reaction under strong light-matter coupling. They argue the “conspicuous absence” of cavity-altered effects in the system provide a new data point for help benchmark mechanisms of polariton chemistry.
“Dr. Weichman’s paper deals with a highly exciting and controversial field of intense current interest: whether polaritons, formed by strong light matter interaction, can be used to affect chemistry,” said Dr. Lian. “Her work shows convincingly that strong coupling of the CH stretching mode of CHCl3 molecules with a cavity does not affect their reaction with CN radical. This observation on an important class of reactions with a relatively simple model system provides important data to test theoretical models.”
Prof. Weichman, whose first first-author paper was published in JCP back in 2013, said receiving the JCP Best Paper by an Emerging Investigator Award is “extremely meaningful” to her.
“I have enjoyed being a part of the community that publishes in JCP throughout my career,” she said. “It feels like a full-circle moment that I was able to publish one of my first independent papers in JCP — and that it is being recognized in this way.”
A trained experimental physical chemist and spectroscopist, much of Prof. Weichman’s career has centered on the use of novel spectroscopic techniques in studying the structure and dynamics of molecules to better understand them as quantum mechanical systems.
“As a PhD student with Prof. Neumark at [The University of California, Berkeley], I used high-resolution anion photoelectron imaging to study an array of cold radicals, clusters, and transient reactive complexes,” said Prof. Weichman. “The highlights of this work were transition state spectroscopy experiments that illuminated discrete quantum resonances supported along the reaction coordinates of benchmark molecular reactions.”
“Subsequently, in my postdoc work with Dr. Jun Ye at JILA/[University of Colorado Boulder], I used cavity-enhanced frequency comb spectroscopy to resolve the quantum states of unprecedentedly large molecules like the C60 fullerene,” she added.
At Princeton, her team applies spectroscopic techniques drawn from atomic, molecular, and optical physics to important chemical problems. Currently, the team is interested in examining chemistry under strong light-matter interactions — the subject of the winning paper. They’re also developing precision and cavity-enhanced spectroscopies for astrochemistry and climate science.
Building on the success of this paper, wherein they studied a near-barrierless reaction, Prof. Weichman’s lab intends to study reactions with higher barriers relying on infrared excitation in order to proceed, believing it will give them a better chance of seeing cavity-modified behavior.
“Stay tuned!” said Prof. Weichman.
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Contact:
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