Tribute to Benjamin Widom - ACS Publications - American Chemical

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Special Issue Preface pubs.acs.org/JPCB

Cite This: J. Phys. Chem. B 2018, 122, 3203−3205

Tribute to Benjamin Widom range of subsequent theoretical and computational developments. Most importantly, this theory produced a new exact expression for liquid-state chemical potentials. Ben referred to this approach as “potential distribution theory”, and its implications include what is now widely known as the “Widom particle insertion” method. In the same paper, Ben also described applications of potential distribution theory to liquids, including the derivation of generalized van der Waals and lattice models of fluids. In 1978,63 Ben extended potential distribution theory to heterogeneous systems such as the interface between a liquid and its vapor, opening up a new theoretical approach to inhomogeneous systems. The power and scope of potential distribution theory demonstrate to students of theoretical science that a purely analytical result, achieved without any apparent reference to simulations, can in the future have an enormous impact on computation. Ben’s work revealed that the forces relevant near the triple point,23 where solid, liquid, and vapor phases are in mutual equilibrium, are quite different from those important near the critical point,28 where liquid and vapor phases become indistinguishable. As explained in a 1967 paper,31 “Intermolecular Forces and the Nature of the Liquid State”, Ben established that, while shortranged repulsive forces dominate near the triple point, long-ranged attractive forces dictate the characteristic phenomenology of the critical point. With this work, Ben established the pathway from the 19th century theory of van der Waals to a comprehensive theory of the liquid state, answering the implied challenge of Landau and Lifschitz. The influence of the 1967 paper is next described by the “W” of WCA perturbation theory: At the ACS meeting in Washington celebrating Ben’s 90th birthday, it was striking to see speaker af ter speaker citing the many pioneering papers by Ben Widom that strongly inf luenced their research. I know I would speak for David Chandler and Hans Andersen in saying that the Ben Widom paper that changed our lives forever was B. Widom, Science 157, 375 (1967). It is a model of clarity and conciseness, exemplif ied by its one sentence abstract: “Liquids ref lect in their bulk properties the attractions and repulsions of their constituent molecules”. It provided deep physical insight into the basic physics of simple liquids and its connection to the successes and limitations of the van der Waals equation. Ben’s simple picture that attractive intermolecular forces in uniform dense liquids essentially cancel explained the accuracy of the hard sphere model and provided the key idea that led to the development of the WCA theory and to many other advances. Ben Widom’s scientif ic leadership, his generosity, and his open and supportive personality serve as a continuing inspiration for all of us. Thank you, Ben Widom! (John Weeks, University of Maryland) Ben’s focus on the contemporary generalization of the ideas of van der Waals is evident to curious Cornell students and drivers around Ithaca who have noticed the letters VDWAALS on his New York State license plates. Also of formidable impact is the development of “Widom scaling”,27,28 which represents a crucial milestone in the solution

Cornell University Photography

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hen Ben Widom was awarded the Boltzmann medal in 1998, the citation read, “For his illuminating studies of the statistical mechanics of fluids and fluid mixtures and their interfacial properties, especially his clear and general formulation of scaling hypotheses for the equation of state and surface tensions of fluids near critical points.” The words “illuminating” and “clear” are especially well-chosen, for Ben Widom has brought light and clarity to numerous branches of statistical mechanics as well as to the understanding of anyone who has heard him speak in the classroom or at a scientific meeting or who has read any of his publications. Ben has reminded audiences103 that, as recently as the middle twentieth century, Landau and Lifschitz were able to state with their customary authority that, in contrast to solids and gases, no general method existed to compute the thermodynamic properties of liquids. That this statement no longer holds is due in large part to Ben’s pioneering insights and accomplishments. Any partial enumeration of Ben’s research highlights must include his 1963 paper,21 “Some Topics in the Theory of Fluids”. This exceedingly influential work laid the foundation for a wide © 2018 American Chemical Society

Special Issue: Benjamin Widom Festschrift Published: April 5, 2018 3203

DOI: 10.1021/acs.jpcb.8b00129 J. Phys. Chem. B 2018, 122, 3203−3205

Special Issue Preface

The Journal of Physical Chemistry B

precisely on time, in the bottom right-hand corner. In 2010 he and I were teaching at a mini-school for students attending Faraday Symposium 146. Ben kicked off the Seminar in his usual immaculate style, setting the bar for any subsequent lecturer. Moreover, he used what appeared to be PowerPoint. Af terward a student joined Ben and asked: “Professor Widom what font do you use for your slides? I really like this.” It was a serious question. Ben smiled and said: “Ah. Do you not recognize this?” Standing nearby, I laughed. For his lecture, Ben had scanned in his own hand-written notes and thereby had developed his own Widom Font. (Bob Evans, University of Bristol) An example of Widom Font may be found in the cover art. Since his arrival at Cornell, Ben’s faculty office has been a major center of statistical mechanical research. However, all of his group members and visitors over the last four decades, as well as other Cornell theoretical chemists, know that he has a branch office: the Souvlaki House restaurant. Statistical mechanicians from around the world have fond recollections of the regular Saturday pizza lunches with Ben. While he is broadly tolerant of a wide range of tastes in pizza, lunch goers quickly recognize his partiality to feta and garlic and to pepperoni and pepperoncini as toppings. A former lunch regular elaborates: Prof. Widom would take the entire group, students, postdocs, and visiting scientists, for lunch each weekend to a very f ine Greek restaurant. It was always f riendly and informal, and during the walk down there f rom the lab, and on the way back, Prof. Widom would take the time to speak with each of us individually. He would ask f riendly questions about how things were going, not just scientif ically but in broader terms. The kindness shone right through, out of his eyes and into the gorgeous af ternoon around us. Also not to be forgotten: no matter how large or small the group, Prof. Widom had a “formula” for estimating with unfailing accuracy precisely how much food was necessary. Never too much, nor too little, just right. (Avik Chatterjee, State University of New York, College of Environmental Science and Forestry) In addition to applying his analytical skills to predict pizza consumption by graduate students, Ben is known for bringing his deep understanding of probabilities and his scientific judgment to the poker table. He continues to be a regular member of a poker game that has existed in various forms around the Cornell Chemistry department since the 1940s. One of Ben’s younger colleagues notes: When Ben stays in, and then starts betting heavily, get out. No microstate has been left out of the equation. But then, he could be bluf fing... (Kyle Lancaster, Cornell University) Other colleagues have engaged Ben in different forms of friendly competition: Looks like I am fated to be ten years behind my dear colleague Ben Widom, from Stuyvesant through Columbia to Cornell. In catching up, chess did not work; I did not even try poker. Maybe I did pass him just one time, in appointments with Dr. Nap. It has been a wonderf ul 52 years here with Ben, Cornell’s intellect, and the f inest teacher our trade has given us. (Roald Hoffmann, Cornell University) In addition to the poker table and the chessboard, there is the football field: I have always been awestruck by your exceptional talents as a theoretical chemist and extraordinary ability as a lecturer. But, there is one area where you are a mere mortal; that has to do with your support for the NFL’s New York Football Giants. How someone with so many gif ts and talents could choose such a team (especially this year, 2017)well, I will never understand it. However, fear not! The Philadelphia Eagles NFL fan base is accepting new applications, and since I have been a lifelong Eagles football fan (f rom my South Jersey/Atlantic City upbringing), I can say with great conf idence that

of one of the most important and challenging problems in statistical mechanics of the 20th century: the mathematical interpretation of thermodynamic properties near a critical point. Thermodynamic properties, which generally display smooth dependences on variables such as temperature and number density, show characteristic mathematical singularities near a critical point. Singularities for different properties are linked by mathematical relationships, whose origin Ben was able to explain by postulating that the free energy density is an unknown generalized homogeneous function of two variables. Ben’s remarkable insight set the stage for the development by Wilson of the renormalization group approach, a revolutionary analytical technique that provided a deep understanding of the mathematical description of critical phenomena. While primarily known as a theorist, Ben also went into the laboratory to further our understanding of critical phenomena. His experimental studies with Lang58,59 of the approach to a tricritical point, at which three phases become indistinguishable, provided experimental verification in a four-component system of the newly developed view of critical phenomena. A recurring theme throughout Ben’s career is the molecular nature of liquid interfaces. He has made foundational contributions to the theory of line tensions and surface tensions, which quantify the reversible work associated with the formation of contacts between two or more liquid phases. With John Rowlinson, Ben wrote the authoritative work on this subject, “The Molecular Theory of Capillarity” (1982).73 Ben has continued to identify and contribute to important current problems in statistical mechanics, ranging from phase behavior in microemulsions78 to the fundamental origin of the hydrophobic effect133 to the dynamics of charged polymers.107 As with his early work, each Widom paper brings light and clarity to a complex physical or chemical problem. Ben taught chemistry at Cornell University for more than 50 years. His lectures in the graduate level statistical mechanics course became legendary, and the clarity of his presentation of the subject is also evident to every reader of his undergraduate textbook.145 Perhaps less well-known in the research community is his teaching of introductory chemistry. Students in Honors General Chemistry may not have known of the research accomplishments of the instructor guiding them through the mysteries of multiple equilibria, but they surely appreciated the clarity of his presentations and his remarkable work at the chalkboard. Realizing that, as far as anyone knew, none of his course lectures had been recorded, colleagues and collaborators encouraged him to give a lecture at the chalkboard in his inimitable style, which could be preserved for the future. The resulting lecture on potential distribution theory delivered in 2017 is publicly accessible through Cornell’s streaming service, CornellCast. Viewers may watch Ben begin his lecture at the upper left-hand corner of the board and conclude in the lower right, as next described by two colleagues: Ben enters the small seminar room which has blackboards on three walls. He is introduced and begins speaking and answering questions. Using a piece of chalk he records salient points, equations and pictures on the left blackboard. Once that is f ull he moves to the one in f ront, then to that on the right. Af ter 50 min his conclusions f ill the last lines on the right blackboard, the seminar is over and 10 min are lef t for discussion. (Anneke Levelt-Sengers, National Institutes of Standards and Technology) All mortals need heroes; scientists are no exception. Ben is one of my heroes. His articles inf luenced hugely my own choice of research topics. And who can forget Ben’s remarkable blackboard lectures where he starts writing in the top lef t-hand corner and f inishes, 3204

DOI: 10.1021/acs.jpcb.8b00129 J. Phys. Chem. B 2018, 122, 3203−3205

Special Issue Preface

The Journal of Physical Chemistry B you will be welcomed with open arms into the throng of f ull-f ledged Eagles’ supporters. With that accomplished, you will truly be the complete renaissance man and extraordinary in all aspects of life. (Rick Cerione, Cornell University) Ben’s mentoring of group members extended well beyond the lunch table at the Souvlaki House. According to a former graduate student: For me Ben Widom will always be an example of Scientist, Human and Gentleman. I only wanted to recall the story of one of my f irst papers written as a graduate student in Ben’s group. He encouraged me to do the scientif ic project, completely rewrote the paper that I prepared af ter doing this, checked and corrected all calculations and all mistakes, both scientif ic and grammar. But at the end he refused to be the coauthor because, as he claimed, I expressed a vague idea how to do it. It was a surprising lesson to me. It stimulated my desire to do more scientif ic projects. But I will never forget how Ben Widom put me on this road of doing research. I am happy to stay at this road and I wanted to thank Ben for this! (Anatoly Kolomeisky, Rice University) In addition to members of his research group, his younger faculty colleagues have experienced his warm personal interest in them and their work: Ben has been very caring about his younger colleagues and their research achievements. Now and then C&EN publishes a news piece on our work. I would then get an extra copy of the magazine in my mailbox f rom Ben, with a handwritten note clipped to the f ront, something like “Peng - I thought you would like another copy of this issue...presumably one of many...Very interesting...Ben” (Peng Chen, Cornell University) As a younger colleague, I am always impressed by his love for science. At the age of 90, he still comes to work pretty much every day and his mind is as sharp as a 19-year old. Ben is also a great man to talk to as he always makes me feel at ease when I talk to him. (Hening Lin, Cornell University) Professor Ben Widom is an erudite and kind gentleman and is always most engaging to talk to. (Yimon Aye, Cornell University) Ben is so much more than just a legend in Theoretical Chemistry. He is one of the kindest and most genuine people that I knowand quite a formidable poker player. (Robert A. DiStasio, Jr., Cornell University) From brief conversations in the hallway to sharing pizza at the Souvlaki House to attending his extraordinarily illuminating seminars timed to clockwork precision, I feel fortunate to know Ben. Ben is a truly inspirational colleague: a brilliant scholar, a great teacher, and a genuinely warm and kind person. (Nandini Ananth, Cornell University) And Ben is enthusiastically appreciated by more senior colleagues: Ben was Crucial to the fact that I am now “Emeritus” at Cornell. We would not have come except for him. (Michael E. Fisher, University of Maryland and Cornell University) I f irst encountered Ben Widom as a graduate student at Oxford, when he gave a course of lectures on Critical Phenomena as IBM Professor during the 78−79 academic year. The legendary clarity and lucidity of his lectures made an immediate and extraordinary impact on me. I have subsequently had the great good fortune to have had Ben as a Cornell colleague for over 30 years. During that time he has been a constant source of inspiration as scientif ic researcher, teacher, and human being. (Greg Ezra, Cornell University) I can think of no one who exceeds Ben in the clarity of his seminar talks and teaching generally, all delivered without notes. He has been a tremendous resource for all of us. (Bob Fay, Cornell University)

My meetings with Ben Widom were few but enchanting. His talks always dealt with f undamental insights and properties. Here I want to renew thanks for encouragement Ben gave 25 years ago. In pursuing experiments on fluids at high pressures, Dor Ben-Amotz and I examined temperature-density diagrams for many fluids. We found an intriguing empirical correlation between two prominent generic properties, both nearly linear and known for more than a century. Ben confirmed that the correlation had not been recognized. One line had the quaint name, “line of rectilinear diameters”. The other line, which we dubbed the “Zeno line”, was the locus of f luid points for which the compressibility factor, Z = P/ρRT = 1. The correlation between them remained mysterious until a few years ago. Then V.L. Kulinshii introduced a remarkably simple projective transformation. The linearity of the Zeno line and its relation to the binodal curve emerged as geometrical consequences of an isomorphism of real fluid diagrams with the lattice gas model, equivalent to the Ising spin model. A nice link with universal insights of Ben Widom. (Dudley Herschbach, Harvard University) It is late Thursday afternoon in 119 Baker Laboratory at Cornell, and the weekly departmental chemistry seminar is about to begin. Attendance varies according to the speaker’s field, but one may be sure that regardless of the subject Ben and Joanne Widom are already seated. Their presence, together, reminds the rest of us that chemistry really is a community. The organizers of the First Liquid Matter Conference of the European Physical Society, held in 1990, knew exactly whom to ask to summarize the substance of the research reported, to assess the current state of the physics of liquids, and to predict the future of the field. In a 40 min lecture, which was later published in the conference proceedings,103 Ben succinctly met the first two goals, but in approaching future predictions reminded the audience of the story of Fermat’s last theorem. Fermat wrote that he had proven the result but was unable to fit the proof into the margin of his manuscript. Ben concluded, “Similarly, I was going to predict for you, with great certainty, the future of liquid-state physics, but...” In like spirit, we might finish with a precise and detailed prediction of the influence of Ben’s research achievements on future generations of physical scientists and engineers, but... What is certain is that Ben’s work and personal style of scientific research have had a remarkable impact and that his example will long continue to illuminate and clarify our path forward.

Roger F. Loring

Cornell University

Kenichiro Koga

Okayama University

Dor Ben-Amotz

■

Purdue University

AUTHOR INFORMATION

ORCID

Kenichiro Koga: 0000-0002-1153-5831 Dor Ben-Amotz: 0000-0003-4683-5401 Notes

The reference numbers in the text refer to the list of Publications of Benjamin Widom (DOI: 10.1021/acs.jpcb.8b00125).

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DOI: 10.1021/acs.jpcb.8b00129 J. Phys. Chem. B 2018, 122, 3203−3205