# How does a beginner condensed matter theorist working on real materials, get up to speed?

I asked this on Physics.SE and got recommended here.

More precisely, as a condensed matter theory PhD student, I am often overwhelmed by the wide variety of chemical formulas that experimentalists trot out for their results. I'm thinking about the cuprates, transition metal dichalcogenides, iron pnictides, SrRu with O$$_3$$, O$$_4$$, O$$_7$$, and many more.

• +1. Welcome to our new community and thank you so much for contributing your question here! We hope to see much more of you in the future !!! After talking to some colleagues, I narrowed down your question to make it more answerable. We want just one question per post, so if a week after this question went up, you want to ask a follow-up question about those specific cases you wrote about at the end (for example), you'd be very welcome to ask it then! Nov 17 '21 at 0:13
• After talking to more colleagues, it seems that you also wanted to ask something like "how can you look at the periodic table and decide which compound will exhibit interesting physics?". That's a different question from "I'm overwhelmed with chemistry language, what do I have to learn?". I'd recommend asking the second question separately in about a week, if the answers you get here don't help! Nov 17 '21 at 0:36
• Thanks for being a more welcoming SE group than others. I will see how to revise the later questions if need be Nov 18 '21 at 16:26
• My question definitely was more in the latter. I'm in a theory group that has no connection with chemistry, but I was wondering where a lot of experimental condensed matter groups decide on materials to study, so I'll ask that question on another post since this seems to be more chemistry career advice as is. Nov 18 '21 at 16:36
• your 3 downvotes to people who are genuinely trying to help you, has caused your question to exit the network's "Hot Network Questions" list, meaning that the chances of your question being seen and answered by more people is reduced. You've also downvoted more in the last 24 hours than our entire list of 3500+ users have (in total!) over a span of weeks. I'll edit each answer in case you want to change your mind on those votes. Nov 18 '21 at 19:44

Welcome to the club of academic migrants! I didn't take any university-level chemistry courses during my undergrad years (except a special topics course for graduate students called "bioelectronics" which one might say was more physics and biology than chemistry). I was much more interested in physics and biology (and math) than chemistry, so I pursued a double major and double minor with my majors being "BMath in Applied Math" and "BSc in Honours Science", with the minors being in Physics and Biology.

However, my PhD ended up being granted from a chemistry department, and in recent years I probably worked more in quantum chemistry than in any other field. I know exactly how it feels.

It might seem hypocritical for me to say this, because I personally didn't do this, but hindsight is 2020 (or in my case, maybe even 1970 since my early lack of interest in chemistry might even trace back to my family always talking about physics, math and biology but rarely chemistry). It sounds like you're a relatively new PhD student and will have to take graduate-level courses anyway, so I hope my advice (based on what I'd probably do if I could turn back time) will be useful for your academic career: I'd recommend taking the following chemistry courses if available: inorganic chemistry, transition metal chemistry, heavy-metal chemistry (involving lanthanides and actinides), solid-state chemistry. The following topics might also be of interest: quantum chemistry, computational chemistry (lab), main group chemistry.

For quite some time, I've wanted to audit some of those courses, but I can't do it during COVID and during an extremely busy teaching term. If you were to ask for my advice (considering that my background is similar to yours, as well as my career trajectory, except that I was in your shoes many years ago), I would say to take those courses as early as possible! A lot of (or almost all of?) applied materials physics is chemistry.

I'm grad student about to finish their PhD, so you may find my perspective valuable.

For reference, my undergrad degree was in physics and math, where I did big data analysis on high energy data gathered at CERN. I had some much earlier experience working in a condensed matter lab, yet gained very little (to no) chemistry experience. To date, I have never actually taken a condensed matter course -- and don't intend to. I likewise don't have any specialized training in chemistry, and never took a chemistry class.

Despite this, I feel that I've developed a strong enough understanding of the field to curate my own interest and pursue my own problems. This is in part due to a research mindset that I inherited from my supervisor, and in part due to my own personal preferences toward learning.

The mindset is as follows: Find some problem that interests you enough that you'll throw everything you got at it. Maybe you know nothing about the field -- no general knowledge, no specialized techniques, absolutely nothing. It's like staring out at an ocean -- and condensed matter is a vast ocean -- and not knowing how to pass the beach. Don't fret. Pursue your problem with as much zeal as your interest can muster. Learning everything related to this problem; and with time, effort, and some help, you'll find before you a tiny island of knowledge, deep in the scientific ocean.

Some people might say (and you might feel) that it is necessary to take a class about X, Y, and Z in order to even start doing proper research. But homework -- simple problems that have a clear answer in a book -- will only have you playing in the shallows. Yes, you should calculate and do problems, perhaps even from a book (or paper) if it helps, but always in pursuit of your problem.

These smaller problems orbiting your goal will form the beaches of this tiny island of knowledge. And it is that island which will define your unique perspective as a researcher, and allow you to see farther in the scientific ocean than you could if you stayed in the shallows. And with time, and more island forming research in the deep, you'll have an archipelago to call your own.

Essentially, what I mean by this bit of philosophical mumbo jumbo is: dive deep into an interesting problem. Your own efforts in solving the problem will provide you the ground-level knowledge needed to do other things in your field. And perhaps most importantly, it is the only way to actually learn how to research -- doing research.

This is definitely just my perspective, one which is informed by my experiences. No doubt I am on the extreme end of being class anti-oriented.

As a personal example, I started my theory career studying the Fe-based superconductors (pnictides and chalcogenides). In particular, I chose one material in that broader family -- FeSe -- and studied the hell out of it. Not only are many of the Fe-based superconductors electronically similar, in part owing to the similarities in their symmetries, but I find that the tools I learned translate to other unrelated materials as well.

In real materials, there are also many different types of measurement techniques and experiments: conductance, photoemission, scanning tunneling microscopy, to name a few. I find it can be overwhelming at times, especially when some critical new research in the field depends on a set of techniques which are entirely new to me. But it's in these novel moments that I find the chance to develop my best physics intuition. And a lot of the time, these many different measurements can be related to a few key concepts -- e.g density of states (DOS) shows up everywhere.

Lastly, as a new theory researcher you may consider exposing yourself to cutting-edge numerical methods, such as the Density Matrix Renormalization Group (DMRG), machine learning (ML), or Density Functional Theory (DFT). It's a bit of a myth that you need to invest your entire graduate career in order to learn these things, or that you won't have the opportunity to learn them if your supervisor isn't an expert. There are actually a number of readily accessible tools and codebases from which one can start: QuantumEspresso=DFT, ITensor=DMRG, and Keras/TensorFlow=ML are just a few that I've used.

These toolsets aren't just useful blackboxes either, but a fully functioning code that has the potential to teach you the method. It can be challenging to build up a codebase from scratch, as there a lot of new things to learn, and all the pieces have to fit just right in order for it to properly compute. But a fully functioning codebase can have pieces rewritten piece by piece, with the understanding that if it doesn't compute, then it's your piece that's bad. There are also tons of related workshops where you can learn from the pros.

This top-down approach to novel numerical methods is how industry teaches machine learning, since it's pedagogically faster, and allows one to get results while they learn. If you're supervisor talks about one of these techniques, but they themselves don't have experience coding them, then they'll likely be super impressed if you did. You might suddenly find yourself becoming extremely valuable to your research group.

• +10, another great answer by this new user! Where have you been all this time? I agree with so much of what you're saying. I assume though, that you did your PhD in Europe? Fewer courses are required for PhDs in Europe vs in Canada where OP is, so it might not be a bad idea of OP to take a couple advanced (and very relevant) chemistry courses if they're really "overwhelmed with the variety of chemical formulas". Don't get me wrong, I did pretty much exactly what you did: I got my PhD from a chemistry department and never took a chemistry course (I just learned everything by working Nov 18 '21 at 5:42
• passionately on one problem to which I devoted almost all my efforts). However, it's now been many years since then and I am very eager to audit some advanced inorganic chemistry lectures as soon as I get a chance. After working in the field for many years beyond my PhD, I think chemistry (especially physical chemistry, solid-state chemistry and applied quantum chemistry) is a fascinating subject but there's something more appealing to me about taking or auditing the courses versus taking it completely upon myself to independently arrive at the same level of knowledge. Nov 18 '21 at 5:47
• Ya I totally agree. I'm not ideologically opposed to classes, and course work is the foundation for most people's understanding (including my own), especially for someone coming out of undergrad. However, I found classes (and likewise workshops and theory schools) were more valuable later in my grad career than earlier. At that stage, they provide rapid exposure to a broader field; and especially useful if one has already developed a sense of personal incentive and self-education to guide them without grade-based busy work. Nov 21 '21 at 20:02
• Very true about it being possible for courses to be more valuable later in the academic career than earlier. Later it can get harder and harder to find the time to take a course though, and if a student is early in their PhD program and has to take courses anyway, some specific courses could be worthwhile especially if they say they're "overwhelmed by the wide variety of chemical formulas [...] cuprates, transition metal dichalcogenides, iron pnictides, SrRu with O3, O4, O7,.." My friend Steve Winter did his undergrad in a Chem department, and knows those materials better than anyone I know. Nov 21 '21 at 20:13
• I worry that if we keep commenting here, the system will ask us to move to chat. For this reason: meta.stackexchange.com/q/353643/391772, I recommend not to click on the button, which would create a new chat room. Instead we could talk in this one: chat.stackexchange.com/rooms/107323/modeling-matters. I completely agree that the course requirements for a PhD in USA and Canada are not the best for the students, and it's why people in UK and Europe are expected to finish in 3 years. The OP is in Toronto and will have to take courses anyway (might as well take the right ones!) Nov 21 '21 at 20:29

Answering "How does a beginner condensed matter theorist working on real materials, get up to speed?" is not as easy as it could appear.

From my own experience, if you are a condensed matter theory PhD student and only focus on condensed matter, you will (should?) grow faster.

In my case, I am a physicist and also made my PhD in theoretical condensed matter physics (developing a phonon laser called SASER). But then, I moved to make a post-doc in an experimental semiconductor group (coming back to my undergrad / master main subject). After the first year, I come back to applying theory to the semiconductor devices studied in the group.

Then, I began to work as professor in my actual university. At the time (2006), the older researchers (all chemist and pharmacist) worked in inorganic chemistry developing materials and in organic chemistry in drug development for different diseases. In order to be inserted in that (new) research lines, I did a lot of individual studies and an organic chemistry course with one of the colleagues I was collaborating with. Certainly the latter "delayed" me a bit.

Now, I can move between condensed matter, structural biology and drug development. So, for me, it was a win-win path.