It might have been noticed by some people, that Cody went through and implemented most (if not all) of your suggestions the other day. For example he removed the "functionals" tag from every question that had it.
It doesn't seem that anyone disagreed in any noticeable way, with anything that he did in this regard.
In preparation for our Private Beta, I also emerged myself in the Drones Private Beta for the 2 weeks leading to ours, and when they had tag issues, they came to agreement this way and in the chat, which Martin has pointed out, we have been doing here as well. I think we should continue to use our "tags" chat room, and also agree on changes via meta questions as they did on Drones SE.
I would also like to make some effort at answering the questions raised in Martin's question, about these:
functionals: I actually do think a functionals tag is appropriate. DFT has been tagged 50 times, but many of the questions
specifically have to do with
functionals development, or
choice of functional:
1) Appropriate functionals for prediction of NMR spectra of transition metal compounds
2) What are the best functionals for transition metal compounds?
3) What is the closest thing we have, to a "universal" density functional?
4) What makes PBE the most preferred functional over other GGA functionals?
5) Is there any DFT code or software that have option to use exact exchange-correlation energy functional?
While many of them do not really have anything to do with the functionals themselves:
1) What is the difference between BDFT and CDFT?
2) What correlation effects are included in DFT?
3) How to evaluate spin exchange parameters of a magnetic material using DFT?
4) Database or repository with values for the Hubbard potential U?
5) How established is density functional theory as a tool in drug design?
I propose the guidelines for using the functionals tag, would be that the question is about the development of functionals or choice of functionals. Everyone seemed to be using it this way anyway, so it did not seem to be a problem that "lost souls" would accidentally use the functionals tag inappropriately.
meta-gga: The question was "what questions should fall into that category."
So far all 5 questions with meta-GGA in the title or question body, would make perfect sense to me. I suspect we will be getting a lot of meta-GGA questions after I advertise on some mailing lists that I've been avoiding doing until we go public. The Minnesota functionals are some of the most popular functionals in existence and they are meta-GGA. The guideline for usage is simply that the question pertains to the use of the meta-GGA approximation.
geometry: The question was "Do you mean molecular structure, or do you mean the mathematical category?" So far all 14 posts using the word geoemtry meant "material structure" (or molecular structure in some cases). We can make this clear in the tag's excerpt. I don't imagine we'll get a lot of questions about the mathematics topic of geometry, except those which have to do with the geometry of materials/molecules. I think most people coming to a specialized SE like this one, will not be using this tag in a problematic way (at least so far, 14 posts have used the term in the same way).
mulliken: The question was "Population analysis? Does it need it's own tag, or would pop actually be better?" and since only one question so far has had "Mulliken" in the question or answer, perhaps we don't need this tag (yet). Thankfully Cody already removed this tag from everything that had it. We can cross this bridge once there's enough questions with "Mulliken" appearing in it, and I agree that mulliken-population-analysis would be better than just "mulliken".
ccdc: Martin points out that we already have databases, and so far it appears that there's only two questions with CCDC in them, so the single question currently tagged with the ccdc tag can have it removed perhaps. Since it seems to have only been used once (in almost 150 questions), it may not be a problem?
u: Thankfully it's gone now, and we have dft-u. But I think this should be dft+u not dft-u, and if "+" is not allowed, we can do dft-plus-u.
kohn-sham: Martin said: "I see the value in this, but it needs a clear scope and it shouldn't be redundant to
dft". I agree, quite a lot of DFT is KS-DFT, so if we have 1000 questions with the DFT tag and 900 of them have the KS-DFT tag, it seems a bit redundant doesn't it? The question is probably more for the followers of the KS-DFT tag (not me). Do they want to be notified all 900 times someone uses KS-DFT? Or only when someone is talking specifically about KS orbitals or the KS aspect of the problem is significant? This perhaps could be up to the followers of this tag to decide (I rarely use DFT so my opinion might be less important).
material-modeling:
Thankfully Cody removed it from all questions that had it.
vibrational: Cody already switched it to vibrations. I propose to keep it that way for now.
soft-question: Martin said: "If you don't know what to type into the tag field, then you might start typing ques and then it'll pop up and populate like mad." I don't know, does anyone here really type "ques" when they don't know what to type? We have only 3 questions out of almost 150, that have this tag, and I was impressed that people knew exactly how to use it, for example Mr. Pie from the MathematicsSE used it properly. This tag is on a lot of other SEs and it's going to keep coming back if we burninate it, so I'd say to keep it.
software: Martin said: "Most questions here will be about software, so what's the point." Certain questions are specifically about the software, and out of almost 150 quesitons this has only been used (in my opinion very correctly) in 17 cases. The DFT tag has been used in 50 cases. Many questions are about the theory or approach to the modeling, not having anything to do with the software.
modeling-software: Thankfully these tags were switched to software. Perhaps modeling-software can be a synonym so that anyone that comes here and types that ends up not making a new tag (like it happened the first time?). I think this was accidentally created because at the very beginning, someone thought that the "software" tag would be for far more than just modeling software.
scan: This was
not a meta tag, it was for "strongly-constrained and appropriately-normed" functionals. Anyway, Cody removed it, which is okay because it only showed up once anyway.
universality: Again this is not a meta tag, it is for the physics concept of universality. The description correctly states "Questions related to universality classes of phase transitions."
education: I think this was created at a time when there wasn't enough tags available to use. It's been used twice, both times in a reasonable way, and we can consider what to do with it if it becomes a problem.
video-lectures, online-course: Cody already switched everything with these, to reference-request. We can make synonyms if they keep coming up.
Summary: functionals, meta-gga, and geometry are in my opinion good tags, and their usage can be described as I did above. If someone has a problem with one of these tags, perhaps we can have a Meta discussion about that tag specifically, as they did on Drones SE for 8 different tags. mulliken and ccdc have not been used much, so whether or not they are needed is something that we can decide once there's more questions (we have existed for only 8 days). u should be dft-plus-u in my opinion, although currently it has been switched to dft-u. The usage of kohn-sham can be decided by someone else, since my opinion on it is maybe not very significant. material-modeling was removed from all questions that had it, and vibrational has been removed from all questions that had it. All the meta tags were in my opinion fine for now, except video-lectures and online-course have been switched to reference-request whenever they appeared, and synonyms can be made if necessary.
