I was encouraged to write about Neil because of wonderful recollections, by Roald Hoffmann, and others, on the AIRAPT website. Probably out of all of the people writing there I knew Neil the least; my interactions with him went on for four months only. And yet his imprint on my scientific life and the way I view science was so considerable that I felt compelled to write.

I met Neil in the summer of 2004 when I came as a visiting scientist to Cornell from Warsaw. Shortly before that I talked with Roald, mentor of my postdoctoral stay (1999-2000) about how greatly I was impressed by studies of matter at high pressures. What impressed me most was the fact that people achieve amazing results in trying to understand what happens to chemical elements, such as lithium, hydrogen or sulphur or iron, at the GPa regime. A chemist is exposed in his daily routine to chemical compounds containing up to 10 or more elements; the variety of physicochemical features associated with broad chemical contents is of course paramount. While those people got excited by what happens to a single element at high pressure! At that time, indeed, ultra-high pressure studies were limited to elements, binaries and seldom ternaries. Meanwhile reactivity, something which is at very core of chemistry, was virtually untouched. I realized that huge chemical pressure may generate matter that is exotic both to chemistry and physics, and I shared this idea with Roald. This probably was the reason why he decided to talk to Neil, who was the next-door expert in high pressure science, and there begun regular meetings, with Roald and Neil as senior scientists, Ji Feng (the then PhD student of Roald's, now full professor at Beijing University) and myself. Most meetings were in Neil's office; I recall that Baker Lab (chemistry) and Clark Hall (physics) were at that time connected by a narrow corridor that passed by the library. Here, both our worlds met. One science joke at that time showed a physicist and a chemist in the loo, with the label "The only place where physics meets chemistry". But our meetings really worked against this stereotype.

The meetings of our quadruplet lasted four months, and then turned into regular meetings comprising Roald's group, attracting more and more young researchers. And generating a lasting collaboration and friendship.

The topic that we pursued in 2004 was the possible metallization of silane, SiH4. This closely followed Neil's idea that hydrogen-rich alloys might superconduct at rather high pressures (this hypothesis was was spectacularly confirmed a few years after). At the time Roald knew about a 2004 work I have published with Pete Edwards about hydrides for hydrogen storage, and he and Neil asked me which hydride should be studied first as a promising target. From what I knew at that time, tetrahydrides were the simplest H-rich systems. Among those, methane seemed impossible to metallize, but silane or germane were worth consideration. Therefore, at Cornell we focused on silane. The theoretical studies we published 2 years later contained two important conclusions: molecular SiH4 would polymerize first to a 2D material, and then - at pretty high pressure, would become metallic. While this particular work did not lead directly to a breakthrough it seems to have inspired many researchers working in the field, and in less than 15 years brought us room-temperature superconductivity in hydrides. How immensely happy late Neil must have been learning about such a spectacular outcome...

My own private recollections of Neil are those of his brightness and wit. And of a particular relation to chemistry that he - the solid state physicist - had.

When looking at the very first plots of the density of states vs pressure that we derived, Neil would immediately exclaim: Look at these disappearing gaps! These were only some very first imprecise curves, but Neil instantly spotted the fact that gaps in the electronic spectrum may easily go down to null for states both below and above the Fermi level but NOT at the Fermi level. This single comment of a great physicist inspired me for years to look at what is known in chemistry as Pearson's hardness... It is nearly certain that Neil never heard of the Maximum Hardness Principle, which is a very chemical concept. Yet, he reinvented it in that moment, independently of Pearson.
Another remarkable impression Neil had on me was when I tried to properly understand the ramifications of the BCS theory. Prompted by my question, Neil generated within a quarter of an hour on two sheets of paper, in a single sitting, all the equations of BCS theory. "This is how a good physicist works!" - remarked Roald before sending me the files.

The collaboration with Neil, Roald and Ji has ultimately led us to publish a review devoted to high pressures, with a clear mission to bridge chemistry and physics; this work has been appreciated by our communities.

Neil's special relation to chemistry was best emphasized in Roald's recollection by saying: "I would say that he was respectful of the understanding that chemists had reached of a complex world; he really wanted to learn how we did it." I should add that - teaching to the first-year physics students at Cornell - Neil presented them with a Periodic Table of elements and asked them to learn it by heart, saying that they will never understand physics of the solid state if they fail to memorize this key periodicity. I wonder whether there exists any other teacher of physics on the planet who is equally considerate, brave, insightful and deep as Neil was... Personally, I was immensely honored to be invited by Neil for dinner, where he expressed interest in higher silver fluorides, the topic that I then intensely pursued, and managed to interest the solid-state physics community in years later after Neil saw its value. Neil insisted on explaining him not only what properties are expected for these materials but also what rationale pushed me to study them. He wanted to know how I knew they would be very interesting.

Neil's wit? There was a lot. A single recollection about his own PhD defense. At that time any PhD Thesis originating from Cambridge could be reviewed exclusively by folks from Cambridge and Oxford. Hence, according to his own words, Neil travelled to Oxford, gave a seminar, and went to the pub with the group of the reviewing professor. Then, at the pub, they were joined by a local group member, who could not make it to the lecture, but managed to reach the pub on time. When introduced to each other, Neil was asked by this individual: -"Which university are you from?" "-I am from Cambridge" - Neil's natural response would follow. -"Oh, do you have any university at Cambridge at all?" - would ask his interlocutor while raising brews overly high. Neil very much appreciated the English humor... I tend to think of Neil as an Englishman in New York.

The last recollection of Neil that I'd like to share is that from Jose Lorenzana, a colleague and collaborator from Rome. Jose recalled Neil visiting a place in Italy that was about to be closed since not enough priority was given in it to "applied science". Neil then fiercely defended the Institute claiming that there is nothing like "applied science"; there are just "applications of science" so that pure science and understanding it brings come first...

These are short glimpses from my memory about how Neil was.