Monday, July 26, 2021

Sage wisdom on computational materials science

Roald Hoffmann and Jean-Paul Malrieu are two of my favourite living theoretical chemists. Both greatly value the role of concepts and intellectual clarity in theory. Hoffmann has featured in 22 posts on this blog.

They recently published a wonderful trilogy in  Angewandte Chemie.

Simulation vs. Understanding: A Tension, in Quantum Chemistry and Beyond. 

Part A. Stage Setting

Part B. The March of Simulation, for Better or Worse

Part C. Toward Consilience

I add this trilogy to my list of 5 papers every computational chemistry student should read, suggested by me a decade ago. [Malrieu is author of one of those and Hoffmann co-author of another.]

Although the trilogy addresses and uses specific examples from computational quantum chemistry it is just as relevant to anyone interested in computational materials science. Actually, I hope that anyone interested in materials science would read and digest it as it gives a sober and balanced perspective about the relationship between theory, simulation, and understanding.

Articles are timely as they address hype about how AI techniques will "revolutionise" materials theory. 

The articles are beautifully written and engage with broader themes such as philosophy of science, culture, art, and politics.

Finally, I just love this photo of the two authors, both in their eighties. the photo reflects some of the joy they find in science, so beautifully expressed in these articles.

I thank Ben Powell for bringing the papers to my attention.

Friday, July 23, 2021

Covid-19 in a different world

 

Covid-19 has turned the world upside down. Different people and communities have had very different experiences. In my state of Queensland, it is almost a different world. To illustrate I share the data above, which prompted a three-day lockdown in Brisbane. For reference, Queensland has a population of 5.2 million.

A number of factors have contributed to the relatively positive situation. Australia is an island. Our borders were closed early. There was unity between state and federal governments. Generally, lockdowns have been pronounced promptly. Although Australians do not like authority and are a rebellious bunch, lockdowns and mask mandates have generally been observed. We are not immune from conspiracy theories and vaccine hesitancy. But, overall we have not been plagued by the same level of "politicisation" that has hobbled other countries. 

In some ways, I feel I am living in a different world.

Yet, some of this good fortune should not lead to pride and complacency. Things may still come unstuck. The Delta variant is spreading in Sydney and half the country is in lockdown. The government vaccine rollout has been dubbed a "stroll out".  Only 12 percent of the population has been fully vaccinated. Australia is currently ranked last among the OECD countries. 

The associated "blame game" has even been featured in The New York Times.

Thursday, July 8, 2021

Is condensed matter physics too abstract?

Condensed matter physics is about the properties of real materials. Real stuff that you can see and touch and that you can use to make very practical things like TV screens and mobile phones. Yet, I find it fascinating and somewhat ironic that in condensed matter theory very abstract ideas and mathematical techniques keep cropping up (and being extremely useful): variable spatial dimensions, imaginary frequencies, topology, Chern numbers, conformal invariance, ...

Yet, there is a danger with abstraction. Theoretical condensed matter is not pure mathematics. Perhaps, too often fancy and beautiful mathematics is prized over physical intuition and insight. Theory may take precedence over experiment. How does one find the appropriate balance?

This is part of broader issues about the role of abstraction and formality in education.

Pierre de Gennes (1932-2007) was arguably the founder of soft matter as a research field, as recognized by the Nobel Prize in Physics in 1991. He began his career working on superconductivity and went on to develop a unified framework to understand soft matter (liquid crystals, polymers, foams, colloids...), introducing ideas such as order parameters, scaling, renormalisation, and universality.

After his Nobel, de Gennes gave many lectures in French high schools, which were then published as a book, Fragile Objects: Soft Matter, Hard Science, and the Thrill of Discovery. I highly recommend it, both as a popular introduction to soft matter, but also to hear the perspective of a great scientist on education and research.

de Gennes spent almost his whole life living and working in France. In the book he rants about the French system, particularly its obsession with entrance exams, mathematics, formality, and the abstract.

“Manual skills, visual acumen, the sense of observation, an interest for the physical world which surrounds us, are all qualities that are neglected or downgraded.”

“To work in a garage seems to me the best initiation to a professional life.”

“Ignorance of the real world causes grave distortions.”

“the positivist prejudice”

I found this fascinating because one thing de Gennes is famous for is showing how some properties of a polymer can be understood by considering a theory involving a vector of dimension n, where n was a continuous variable, in the limit where n approaches zero! That is pretty abstract! But, I guess the point is that he is not against abstraction, exams, and mathematics, per se. Rather, he is against them taking on a life of their own.

de Gennes concerns are also shared by Henri Alloul (well known for beautiful NMR experiments on strongly correlated electron materials) author of Introduction to the Physics of Electrons in Solids. In the Preface, he writes, 

In many countries, teaching traditions have always given pride of place to a formal, and essentially deductive, presentation of the physics, i.e., starting from formal hypotheses and leading up to observable consequences. This deductive approach leaves a purely a posteriori verificational role to observation, and hides the thinking that has gone into building up the models in the first place. Here we shall adopt the opposite approach, which begins with the fact that in science in general, and in solid state physics in particular, the qualitative understanding of a phenomenon is an important step which precedes the formulation of any theoretical development. We thus urge the reader to carry out a careful examination of the deeper significance of experimental observations, in order to understand the need for specific models and carry out realistic approximations.

The debate about abstract mathematics is also central to contrasting views about the Institute for Advanced Study at Princeton.

de Gennes's views would have also resonated with Harry Kroto who shared The Nobel Prize in Chemistry for the discovery of buckyballs. He credited playing with Meccano as a child as very important in his scientific development.

Friday, July 2, 2021

Sweet demonstrations of phase transitions

This week my wife and I did some science experiments with kids, aged about 8-12, at a holiday kids club organised by our church. The first day we did rockets, using the old standbys of baking soda rockets and mentos and coke.

On the second day, we did the science of chocolate. Ten years ago (!) we had done this based on some demonstrations developed at Harvard, described in this paper The Science of Chocolate: Interactive Activities on Phase Transitions, Emulsification, and Nucleation

Teaching kids about phase transitions with ice and steam is not quite as exciting or memorable as them melting chocolate in their mouths. An important scientific idea is:

Physical properties of matter (such as melting temperature) change with differences in chemical composition.

This is illustrated by the different melting temperatures of white, milk, and dark chocolate.

We also tried to mix water and oil, with and without the presence of detergent. This illustrates ideas about emulsification, including hydrophobic interactions. This is relevant to the production of nice smooth and uniform chocolate because the cocoa powder can only dissolve in the cocoa butter when an emulsifier is present.

Discussing chocolate is also an opportunity to discuss Milton Hershey (USA) and the Cadbury family (UK). They were not only philanthropists but were proactive in taking care of employees and their families, e.g. constructing schools, parks, and affordable housing. Richard and George Cadbury developed the garden village of Bournville; now a major suburb of Birmingham. I particularly like this sentence in the Wikipedia entry on George Cadbury, showing how he was far ahead of his time.

In 1901, disgusted by the imperialistic policy of the Balfour government and opposed to the Boer War, Cadbury bought the Daily News and used the paper to campaign for old age pensions and against the war and sweatshop labour.[4]

Other scientific articles of interest include the following. The first two discuss how there are six different polymorphs (crystal structures) of chocolate. The competition between these states comes into play with tempering, snapping, shine, and smoothness. [Aside: In general, calculating the relative energies of different polymorphs of molecular materials is a major scientific challenge.]

Chocolate: A Marvelous Natural Product of Chemistry, Ginger Tannenbaum

Using Differential Scanning Calorimetry To Explore the Phase Behavior of Chocolate Michael J. Smith

The kitchen as a physics classroom Amy C Rowat, Naveen N Sinha, Pia M Sörensen, Otger Campàs, Pere Castells, Daniel Rosenberg, Michael P Brenner and David A Weitz