I am currently a second year PhD student in a 5 year direct-entry PhD program, studying experimental chemistry. Another important consideration is that I am on the first year of a 4 year top-tier doctoral scholarship. Also, I haven't written my comps yet and I haven't really started my thesis research (I have worked on a several small, unrelated projects). My research focus is on spectroscopy of inorganic complexes, but we are kind of a jack of all trades lab. I do synthesis, crystallography, spectroscopy, and computational chemistry.
I have a lot of experience in computational chemistry, but I have never worked in theoretical chemistry (i.e., quantum chemistry). Since I started doing computational chemistry, the topic has always interested me. I read some textbooks, but my math/physics/programming skills were never really good enough to test whether I really understood by writing codes. I am now of the opinion that the subject is specialized enough that the only way to learn it is to do research in that area. During the lockdown, I spent a lot of time studying math and elementary programming, and I have realized that I actually like this kind of thinking. I feel unsatisfied by the lack of rigorous math and physics in my current research. I talked to some theoretical chemists and they are convinced that I can learn the field well enough to do a PhD on an electronic structure theory topic if I apply myself, so I am seriously considering making the switch. Moreover, I think the career prospects are better with that skillset. My research area is fairly niche, so I think it pretty much only leads in the academic direction, which, as we all know, is far from a sure thing, whereas quantitative skills are useful in all industries.
I don't know what to do and having the decision hanging over my head is really stopping my from progressing. The way I see it, I could master out and apply into a new PhD program in this area (possibly in Europe), however, I don't know how it would look to master out on a doctoral scholarship. I could simply transfer to a new school/lab and put off my comps, which would make my PhD much longer. this seems more feasible, but I don't know how the topic switch would fit in with my scholarship, which is based on a proposal related to my current research topic. Or I could complete my PhD, take some relevant courses, and try to pursue this later.
I have talked to my PI about it and he thinks it is totally feasible to pursue such a change of focus after my PhD, but my understanding is that postdocs are supposed to already be experts in their field, so I don't know how I would go about learning such a specialized topic after my PhD, short of doing another degree. Is something like this really possible?