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JCP Spotlight Collections

The Journal of Chemical Physics has created a new Perspectives section, featuring invited papers on topics currently generating a great deal of interest in the research community. JCP Spotlight Collections, which will be home to the collected perspectives, along with the seminal articles they reference, provide a comprehensive look at the history of the field and where it is headed.

Marsha I. Lester discusses JCP's Spotlight Collections (published 15 June 2010).

Perspectives will be a regular feature of the journal and freely available to the community. We hope these collections will be a useful research tool, as well as a valuable resource for those interested in learning more about the broad range of topics in Chemical Physics.


Perspective: Fifty years of density-functional theory in chemical physics

Axel D. Becke
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, CA

Becke Interview (MP3)
Becke

Listen now to Part 1: History of DFT
Listen now to Part 2: Advances in DFT and the future

Abstract Since its formal inception in 1964–1965, Kohn-Sham density-functional theory (KS-DFT) has become the most popular electronic structure method in computational physics and chemistry. Its popularity stems from its beautifully simple conceptual framework and computational elegance. The rise of KS-DFT in chemical physics began in earnest in the mid 1980s, when crucial developments in its exchange-correlation term gave the theory predictive power competitive with well-developed wave-function methods. Today KS-DFT finds itself under increasing pressure to deliver higher and higher accuracy and to adapt to ever more challenging problems. If we are not mindful, however, these pressures may submerge the theory in the wave-function sea. KS-DFT might be lost. I am hopeful the Kohn-Sham philosophical, theoretical, and computational framework can be preserved. This Perspective outlines the history, basic concepts, and present status of KS-DFT in chemical physics, and offers suggestions for its future development.

J. Chem. Phys. 140, 18A301 (2014)


Perspective: Detecting and measuring exciton delocalization in photosynthetic light harvesting

Gregory D. Scholes and Cathal Smyth
Department of Chemistry, University of Toronto, Toronto, CA

scholes Interview (MP3)
Scholes

Listen now to the interview

Abstract Photosynthetic units perform energy transfer remarkably well under a diverse range of demanding conditions. However, the mechanism of energy transfer, from excitation to conversion, is still not fully understood. Of particular interest is the possible role that coherence plays in this process. In this perspective, we overview photosynthetic light harvesting and discuss consequences of excitons for energy transfer and how delocalization can be assessed. We focus on challenges such as decoherence and nuclear-coordinate dependent delocalization. These approaches complement conventional spectroscopy and delocalization measurement techniques. New broadband transient absorption data may help uncover the difference between electronic and vibrational coherences present in two-dimensional electronic spectroscopy data. We describe how multipartite entanglement from quantum information theory allows us to formulate measures that elucidate the delocalization length of excitation and the details of that delocalization even from highly averaged information such as the density matrix.

J. Chem. Phys. 140, 110901 (2014)


Perspective: Bimolecular chemical reaction dynamics in liquids

Andrew J. Orr-Ewing
School of Chemistry, University of Bristol, UK

Orr Interview (MP3)
Orr

Listen now to the interview

Abstract Bimolecular reactions in the gas phase exhibit rich and varied dynamical behaviour, but whether a profound knowledge of the mechanisms of isolated reactive collisions can usefully inform our understanding of reactions in liquid solutions remains an open question. The fluctuating environment in a liquid may significantly alter the motions of the reacting particles and the flow of energy into the reaction products after a transition state has been crossed. Recent experimental and computational studies of exothermic reactions of CN radicals with organic molecules indicate that many features of the gas-phase dynamics are retained in solution. However, observed differences may also provide information on the ways in which a solvent modifies fundamental chemical mechanisms. This perspective examines progress in the use of time-resolved infra-red spectroscopy to study reaction dynamics in liquids, discusses how existing theories can guide the interpretation of experimental data, and suggests future challenges for this field of research.

J. Chem. Phys. 140, 090901 (2014)


Perspective: Crystal structure prediction at high pressures

Yanchao Wang and Yanming Ma
Institute for Research in Fundamental Sciences (IPM)
State Key Laboratory of Superhard Materials, Jilin University, Changchun, China

Ma Interview (MP3)
Ma

Listen now to the interview
Listen now to the interview (Chinese)

Abstract Crystal structure prediction at high pressures unbiased by any prior known structure information has recently become a topic of considerable interest. We here present a short overview of recently developed structure prediction methods and propose current challenges for crystal structure prediction. We focus on first-principles crystal structure prediction at high pressures, paying particular attention to novel high pressure structures uncovered by efficient structure prediction methods. Finally, a brief perspective on the outstanding issues that remain to be solved and some directions for future structure prediction researches at high pressure are presented and discussed.

J. Chem. Phys. 140, 040901 (2014)


Perspective: Tipping the scales: Search for drifting constants from molecular spectra

Paul Jansen, Hendrick L. Bethlem and Wim Ubachs
1Institute for Research in Fundamental Sciences (IPM)
Department of Physics and Astronomy, LaserLaB, VU University Amsterdam

Ubachs Interview (MP3)
Ubachs

Listen now to the interview

AbstractTransitions in atoms and molecules provide an ideal test ground for constraining or detecting a possible variation of the fundamental constants of nature. In this perspective, we review molecular species that are of specific interest in the search for a drifting proton-to-electron mass ratio μ. In particular, we outline the procedures that are used to calculate the sensitivity coefficients for transitions in these molecules and discuss current searches. These methods have led to a rate of change in μ bounded to 6 × 10−14/yr from a laboratory experiment performed in the present epoch. On a cosmological time scale, the variation is limited to |Δμ/μ| < 10−5 for look-back times of 10–12× 109 years and to |Δμ/μ| < 10−7 for look-back times of 7× 109 years. The last result, obtained from high-redshift observation of methanol, translates into μ/μ=(1.4±1.4)×10-17/yr if a linear rate of change is assumed.

J. Chem. Phys. 140, 010901 (2014)


Perspective: Structural dynamics in condensed matter mapped by femtosecond x-ray diffraction

T. Elsaesser and M. Woerner
1Institute for Research in Fundamental Sciences (IPM)
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie

Elsaesser Interview (MP3)
Elsaesser

Listen now to the interview

AbstractUltrashort soft and hard x-ray pulses are sensitive probes of structural dynamics on the picometer length and femtosecond time scales of electronic and atomic motions. Recent progress in generating such pulses has initiated new directions of condensed matter research, exploiting a variety of x-ray absorption, scattering, and diffraction methods to probe photoinduced structural dynamics. Atomic motion, changes of local structure and long-range order, as well as correlated electron motion and charge transfer have been resolved in space and time, providing a most direct access to the physical mechanisms and interactions driving reversible and irreversible changes of structure. This perspective combines an overview of recent advances in femtosecond x-ray diffraction with a discussion on ongoing and future developments.

J. Chem. Phys. 140, 020901 (2014)


Perspective: Coulomb fluids – Weak coupling, strong coupling, in between and beyond

Ali Naji1, Matej Kanduc2,3, Jan Forsman4 and Rudolf Podgornik3,5
1Institute for Research in Fundamental Sciences (IPM)
2Free University Berlin
3J. Stefan Institute
4Chemical Center
5University of Ljubljana

Naji Interview (MP3)
Naji

Listen now to the interview

Abstract We present a personal view on the current state of statistical mechanics of Coulomb fluids with special emphasis on the interactions between macromolecular surfaces, concentrating on the weak and the strong coupling limits. Both are introduced for a (primitive) counterion-only system in the presence of macroscopic, uniformly charged boundaries, where they can be derived systematically. Later we show how this formalism can be generalized to the cases with additional characteristic length scales that introduce new coupling parameters into the problem. These cases most notably include asymmetric ionic mixtures with mono- and multivalent ions that couple differently to charged surfaces, ions with internal charge (multipolar) structure and finite static polarizability, where weak and strong coupling limits can be constructed by analogy with the counterion-only case and lead to important new insights into their properties that cannot be derived by any other means.

J. Chem. Phys. 139, 150901 (2013)


Perspective: Reaches of chemical physics in biology

Martin Gruebele1 and D. Thirumalai2
1University of Illinois
2University of Maryland

Gruebele Interview (MP3)
Gruebele

Listen now to the interview

Abstract Chemical physics as a discipline contributes many experimental tools, algorithms, and fundamental theoretical models that can be applied to biological problems. This is especially true now as the molecular level and the systems level descriptions begin to connect, and multi-scale approaches are being developed to solve cutting edge problems in biology. In some cases, the concepts and tools got their start in non-biological fields, and migrated over, such as the idea of glassy landscapes, fluorescence spectroscopy, or master equation approaches. In other cases, the tools were specifically developed with biological physics applications in mind, such as modeling of single molecule trajectories or super-resolution laser techniques. In this introduction to the special topic section on chemical physics of biological systems, we consider a wide range of contributions, all the way from the molecular level, to molecular assemblies, chemical physics of the cell, and finally systems-level approaches, based on the contributions to this special issue. Chemical physicists can look forward to an exciting future where computational tools, analytical models, and new instrumentation will push the boundaries of biological inquiry.

J. Chem. Phys. 139, 121701 (2013)


Perspective: Coarse-grained models for biomolecular systems

W.G. Noid
The Pennsylvania State University

Noid Interview (MP3)
Noid

Listen now to the interview

Abstract By focusing on essential features, while averaging over less important details, coarse-grained (CG) models provide significant computational and conceptual advantages with respect to more detailed models. Consequently, despite dramatic advances in computational methodologies and resources, CG models enjoy surging popularity and are becoming increasingly equal partners to atomically detailed models. This perspective surveys the rapidly developing landscape of CG models for biomolecular systems. In particular, this review seeks to provide a balanced, coherent, and unified presentation of several distinct approaches for developing CG models, including top-down, network-based, native-centric, knowledge-based, and bottom-up modeling strategies. The review summarizes their basic philosophies, theoretical foundations, typical applications, and recent developments. Additionally, the review identifies fundamental inter-relationships among the diverse approaches and discusses outstanding challenges in the field. When carefully applied and assessed, current CG models provide highly efficient means for investigating the biological consequences of basic physicochemical principles. Moreover, rigorous bottom-up approaches hold great promise for further improving the accuracy and scope of CG models for biomolecular systems.

J. Chem. Phys. 139, 090901 (2013)


Perspective: Nanomotors without moving parts that propel themselves in solution

Raymond Kapral
University of Toronto

Perspectives
Raymond Kapral (MP3)
Listen now to the interview

Abstract Self-propelled nanomotors use chemical energy to produce directed motion. Like many molecular motors they suffer strong perturbations from the environment in which they move as a result of thermal fluctuations and do not rely on inertia for their propulsion. Such tiny motors are the subject of considerable research because of their potential applications, and a variety of synthetic motors have been made and are being studied for this purpose. Chemically-powered self-propelled nanomotors without moving parts that rely on asymmetric chemical reactions to effect directed motion are the focus of this article. The mechanisms they use for propulsion, how size and fuel sources influence their motion, how they cope with strong molecular fluctuations and how they behave collectively are described. The practical applications of such nanomotors are largely unrealized and the subject of speculation. Since molecular motors are ubiquitous in biology and perform a myriad of complex tasks, the hope is that synthetic motors might be able to perform analogous tasks. They may have the potential to change our perspective on how chemical dynamics takes place in complex systems.

J. Chem. Phys. 138, 020901 (2013)


Perspective: Alchemical free energy calculations for drug discovery

David Mobley
University of California, Irvine

Perspectives
Mobley Interview (MP3)
Listen now to the interview

Abstract Computational techniques see widespread use in pharmaceutical drug discovery, but typically prove unreliable in predicting trends in protein-ligand binding. Alchemical free energy calculations seek to change that by providing rigorous binding free energies from molecular simulations. Given adequate sampling and an accurate enough force field, these techniques yield accurate free energy estimates. Recent innovations in alchemical techniques have sparked a resurgence of interest in these calculations. Still, many obstacles stand in the way of their routine application in a drug discovery context, including the one we focus on here, sampling. Sampling of binding modes poses a particular challenge as binding modes are often separated by large energy barriers, leading to slow transitions. Binding modes are difficult to predict, and in some cases multiple binding modes may contribute to binding. In view of these hurdles, we present a framework for dealing carefully with uncertainty in binding mode or conformation in the context of free energy calculations. With careful sampling, free energy techniques show considerable promise for aiding drug discovery.

J. Chem. Phys. 137, 230901 (2012)


Perspective: Nonadiabatic Dynamics Theory

John Tully
Yale University

Perspectives
Tully Interview (MP3)
Listen now to the interview

Abstract Nonadiabatic dynamics – nuclear motion evolving on multiple potential energy surfaces – has captivated the interest of chemists for decades. Exciting advances in experimentation and theory have combined to greatly enhance our understanding of the rates and pathways of nonadiabatic chemical transformations. Nevertheless, there is a growing urgency for further development of theories that are practical and yet capable of reliable predictions, driven by fields such as solar energy, interstellar and atmospheric chemistry, photochemistry, vision, single molecule electronics, radiation damage, and many more. This spotlight examines the most significant theoretical and computational obstacles to achieving this goal, and suggests some possible strategies that may prove fruitful.

J. Chem. Phys. 137, 22A301 (2012)


Perspective: Advances and challenges in treating van der Waals dispersion forces in density functional theory

Angelos Michaelides and Jirí Klimeš
University College London

Perspectives
Michaelides Interview (MP3)
Listen now to the interview

Abstract Electron dispersion forces play a crucial role in determining the structure and properties of biomolecules, molecular crystals and many other systems. However, an accurate description of dispersion is highly challenging, with the most widely used electronic structure technique, density functional theory (DFT), failing to describe them with standard approximations. Therefore, applications of DFT to systems where dispersion is important have traditionally been of questionable accuracy. However, the last decade has seen a surge of enthusiasm in the DFT community to tackle this problem and in so-doing to extend the applicability of DFT-based methods. Here we discuss, classify, and evaluate some of the promising schemes to emerge in recent years. A brief perspective on the outstanding issues that remain to be resolved and some directions for future research are also provided.

J. Chem. Phys. 137, 120901 (2012)


Special Topic: Photochemistry at Surfaces

Horia Metiu, Associate Editor
University of California, Santa Barbara

Metiu Interview (MP3)
Metiu Interview (MP3)
Listen now to the interview

Abstract This Special Topic Section on Photochemistry at Surfaces contains invited essays by several leading scientists in the field. These essays present personal perspectives on the field and provide an overview of promising areas for future research on photo-initiated processes at surfaces using advanced experimental techniques. The authors focus on fundamental aspects of the field, which also has significant future applications in photovoltaic solar cells and photocatalytic water splitting.

Go to Special Topic: Photochemistry at Surfaces


Perspective: Supercooled Liquids and Glasses

Mark Ediger
University of Wisconsin

Peter Harrowell
University of Sydney

JCP Perspective
Mark Ediger Interview (MP3)
Listen now to the interview

Abstract Supercooled liquids and glasses are important for current and developing technologies. Here, Mark Ediger and Peter Harrowell provide perspective on recent progress in this field. The interpretation of supercooled liquid and glass properties is discussed in terms of the potential energy landscape. Connections are explored between amorphous structure, high frequency motions, molecular motion, structural relaxation, stability against crystallization, and material properties. Recent developments are described that may lead to new materials or new applications of existing materials.
- Photo Credit: Erberto Zani

J. Chem. Phys. 137, 080901 (2012)


Perspective: Quantum or Classical Coherence?

William H. Miller
Department of Chemistry and K. S. Pitzer Center for Theoretical Chemistry, University of California and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, USA

JCP Perspective
Jochen Autschbach Interview (MP3)
Listen now to the interview

Abstract Some coherence effects in chemical dynamics are described correctly by classical mechanics, while others only appear in a quantum treatment—and when these are observed experimentally it is not always immediately obvious whether their origin is classical or quantum. Semiclassical theory provides a systematic way of adding quantum coherence to classical molecular dynamics and thus provides a useful way to distinguish between classical and quantum coherence. Several examples are discussed which illustrate both cases. Particularly interesting is the situation with electronically non-adiabatic processes, where sometimes whether the coherence effects are classical or quantum depends on what specific aspects of the process are observed.

J. Chem. Phys. 136, 210901 (2012)


Perspective: Relativistic Effects

Jochen Autschbach
Department of Chemistry, State University of New York at Buffalo, New York 14260-3000, USA

JCP Perspective
Jochen Autschbach Interview (MP3)
Listen now to the interview

Abstract This perspective article discusses some broadly-known and some less broadly-known consequences of Einstein's special relativity in quantum chemistry, and provides a brief outline of the theoretical methods currently in use, along with a discussion of recent developments and selected applications. The treatment of the electron correlation problem in relativistic quantum chemistry methods, and expanding the reach of the available relativistic methods to calculate all kinds of energy derivative properties, in particular spectroscopic and magnetic properties, requires on-going efforts.

J. Chem. Phys. 136, 150902 (2012)


Perspective on Density Functional Theory

Kieron Burke
University of California, Irvine

JCP Perspective
Kieron Burke Interview (MP3)
Listen now to the interview

Abstract Density functional theory (DFT) is an incredible success story. The low computational cost, combined with useful (but not yet chemical) accuracy, has made DFT a standard technique in most branches of chemistry and materials science. Electronic structure problems in a dazzling variety of fields are currently being tackled. However, DFT has many limitations in its present form: Too many approximations, failures for strongly correlated systems, too slow for liquids, etc. This perspective reviews some recent progress and ongoing challenges.

J. Chem. Phys. 136, 150901 (2012)


Hydrogen: A Fresh Look at High Pressure

Roald Hoffmann, Vanessa Labet, Paulina Gonzalez-Morelos, Neil Ashcroft
Cornell University

JCP Perspective
Hoffmann Interview (MP3)
Listen now to the interview

Abstract Nobel Laureate and Professor Emeritus of Chemistry at Cornell University Roald Hoffmann joins colleagues Vanessa Labet and Neil Ashcroft in talking about their work on hydrogen at very high pressures. While at atmospheric pressures the hydrogen molecule remains one of the few exactly solvable problems as a diatomic molecule, it is not a solved problem under extreme pressure where the molecule’s properties change and the system becomes, as Hoffmann says, “the subject of intense experimental research and an important problem” .

J. Chem. Phys. 136, 074501 (2012)
J. Chem. Phys. 136, 074502 (2012)
J. Chem. Phys. 136, 074503 (2012)
J. Chem. Phys. 136, 074504 (2012)


The Dawning of the Age of Graphene

George W. Flynn
Columbia University

Since the first reports of experiments on stand-alone, single-layer graphene crystals, this remarkable 2-dimensional material has attracted great scientific interest.

JCP Perspective
G. Flynn Interview (MP3)
Listen now to the interview

Abstract Graphene is a single sheet of carbon atoms that constitutes the basic building block of macroscopic graphite crystals. Held together by a backbone of sp2 hybrids, graphene's 2p orbitals form p state bands that delocalize over an entire 2-dimensional macroscopic carbon sheet leading to a number of unusual characteristics that include large electrical and thermal conductivities. Recent discoveries have provided simple methods (e.g. mechanical cleavage of graphite) for preparing laboratory scale samples that can be used to investigate the fundamental physical and chemical characteristics of graphene. In addition a number of techniques have emerged that show promise for producing large-scale samples with the ultimate goal of developing devices that take advantage of graphene's unusual properties. As large samples become available, the possibility grows for applications of this material in solar cell technology (as flexible, transparent electrodes), in composite material development, and in electronic devices.

J. Chem. Phys. 135, 050901 (2011)


Water Cluster Mediated Atmospheric Chemistry

Veronica Vaida
University of Colorado

Vaida JCP Perspective
V. Vaida Interview (MP3)

Listen now to the interview

Abstract The importance of water in atmospheric and environmental chemistry initiated recent studies with results documenting catalysis, suppression and anti-catalysis of thermal and photochemical reactions due to hydrogen bonding of reagents with water. Water, even one water molecule in binary complexes, has been shown by quantum chemistry to stabilize the transition state and lower its energy. However, new results underscore the need to evaluate the relative competing rates between reaction and dissipation to elucidate the role of water in chemistry. Water clusters have been used successfully as models for reactions in gas-phase, in aqueous condensed phases and at aqueous surfaces. Fundamental issues in experimental and theoretical chemical physics remain but that work in this field accelerated recently, driven by the importance of this chemistry in planetary atmospheres including but not limited to Earth.

J. Chem. Phys. 135, 020901 (2011)


Ionic Liquids

Edward W. Castner, Jr.1 and James F. Wishart2
1Rutgers, The State University of New Jersey
2Brookhaven National Laboratory

Castner Interview (MP3)
Castner Interview (MP3)
Listen now to the interview

Abstract Ionic liquids are an emerging class of materials with a diverse and extraordinary set of properties. Understanding the origins of these properties and how they can be controlled by design to serve valuable practical applications presents a wide array of challenges and opportunities to the chemical physics and physical chemistry community. We highlight here some of the signi_cant progress already made and future research directions in this exciting area.

J. Chem. Phys. 132, 120901 (2010)


Frontiers in Electronic Structure Theory

C. David Sherrill
Georgia Institute of Technology

Sherrill Interview (MP3)
Sherrill

Listen now to the interview

Abstract Current and emerging research areas in electronic structure theory promise to greatly extend the scope and quality of quantum chemical computations. Two particularly challenging problems are the accurate description of electronic near-degeneracies (as occur in bond-breaking reactions, firstrow transition elements, etc.) and the description of long-range dispersion interactions in density functional theory. Additionally, even with the emergence of reduced-scaling electronic structure methods and basis set extrapolation techniques, quantum chemical computations remain very time consuming for large molecules or large basis sets. A variety of techniques, including density fitting and explicit correlation methods, are making rapid progress toward solving these challenges.

J. Chem. Phys. 132, 110902 (2010)


Cold and Ultracold Molecules: Spotlight on Orbiting Resonances

David W. Chandler
Sandia National Laboratories

Castner Interview (MP3)
Chandler Interview (MP3)
Listen now to the interview

Abstract There is great interest in the production of cold molecules, at temperatures below 1 K, and ultracold molecules, at temperatures below 1 mK. Such molecules have potential applications in areas ranging from precision measurement to quantum information storage and processing, and quantum gases of ultracold polar molecules are expected to exhibit novel quantum phases. In addition, cold molecules open up a new domain for collision physics, dominated by long-range forces and scattering resonances. There have been major recent advances both in cooling molecules from room temperature and in forming molecules in ultracold atomic gases. As these techniques mature and cold and ultracold samples are more accessible collision studies at previously unavailable energies will be possible. This spotlight article will highlight some of the background and motivation for studying collisions at low energies and will direct readers to recent articles on the recent experimental advancements.

J. Chem. Phys. 132, 110901 (2010)


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