The Periodic Table

Manishearth

12:56 AM

Fingers crossed

@fx is that your opinion or did you ask the SE folks

Chemistry Feeds

1:17 AM

0

Q: Molecularly, why can you straighten or perm hair?

I'm aware that hair can be curly because of the disulfide bond interactions in between cysteine amino acids in alpha-keratin filaments. However, I'm curious as to the biochemistry involved in straightening hair with a straightening iron, as well as with "perming" hair. What happens at the molec...

biochemistry

rcollyer

2:15 AM

@Fx Congratulations on moving into public beta!

A question of mine that was posted on the now defunct theoretical-physics site, and migrated to physics, has languished since I asked it. Would it be appropriate here? Thanks.

Manishearth

2:49 AM

Oh I got the email!

@ChemistryFeeds looks like someone added SE.bio.biochemistry to your feeds

Guess its on purpose, the biochem questions need some cross-collaboration

@rcollyer I don't think so...To me, that seems to be pure QM. Fully on-topic on phy, and sort of off-topic here. If it came here, it would mot likely be migrated off to phy.SE anyway.

Also, DavidZaslavsky mentioned to me that he's averse to migrating to private betas (we're no longer a private beta ^.^, but we may not have enough activity to take care of it)

@rco anyway, I flagged it, let the mods decide

Hey! I lost my editing powers!

Stupid public beta privilege system :p

rcollyer

3:24 AM

@Manishearth it wasn't getting any traction there, so I thought it might do better here (now that you're out of private beta). If not, oh well.

@Manishearth definitely on topic on phys.se, and enough on-topic here, as far as I could tell.

@Manishearth yep, that sucks. you'll get them back soon enough.

Manishearth

@rco the issue is, it's pure QM--no chem involved

rcollyer

I understand that.

Manishearth

On the other hand, you can advertise it on chat here

rcollyer

Yet, it hasn't been touched over there ...

The advert will help, though.

Manishearth

@Everyone: you may find this isteresting to answer:

9

Q: What is the current state of research into $v$-representability?

In their proof, Hohenberg and Kohn (Phys Rev 136 (1964) B864) established that the ground state density, $\rho_\text{gs}$, uniquely determines the Hamiltonian. This had the effect of establishing an implicit relationship between $\rho_\text{gs}$ and the external potential (e.g. external magnetic...

density-functional-theory

rcollyer

3:27 AM

On the other hand, that is why I asked first to see if it would be on topic here.

Manishearth

Actually your issue was low views on TP.. You bumped it, so sit tight and wait for Ron or someone to answer

@rco yeah, that was good

rcollyer

I'm a physicist, so while chem overlaps with QM, I don't know where the boundary is

@Manishearth we'll see if the bump helps. I don't usually frequent phys.se.

And, it is more curiosity at this point ...

Manishearth

It should help, I would say.

rcollyer

Either way, I appreciate the help.

And, wish you guys the best of luck.

Manishearth

3:46 AM

Thanks!

Manishearth

5:43 AM

Test $\ce{H2O}$

w00t

To enable MathJax with chem formatting in chat, use this

F'x

8:24 AM

@rcollyer you're welcome to visit at any time, I'm sure we'll have lots of borderline physics/chemistry questions!

Manishearth

8:37 AM

@Fx Got to use some French on MSO: meta.stackoverflow.com/questions/131932/… (see comments of both posts) . Though it's probably grammatically incorrect somewhere :/

F'x

Parce que (space), si personne ne peut comprendre la fin du poste, il n'est pas utile ;-)

grammar is fine, though

Richard Terrett

Hello all!

F'x

@RichardTerrett hi there

Manishearth

Hello

@fx aah, space. That was a typo though :p

F'x

@RichardTerrett given your field, any input on this one?

3

Q: Are Pulay forces expensive to compute?

In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka ab initio MD) is that the Pulay forces[1,2] that arise from an MD using atomic basis sets are computationally expensive to calculate. While I understand that ...

computational-chemistry molecular-dynamics basis-set

I guess any answer to the same question with Pulay stress would also apply to the calculation of the Pulay forces

Richard Terrett

8:49 AM

@Fx Unfortunately no

Though I know a guy who probably knows

That earlier phys.se question that Manishearth linked seems familiar

I read something in a book about how wavefunctions and densities are not strictly bijective

Manishearth

rears head did somebody mention me?

F'x

@RichardTerrett I'd have to read some more, because I thought the entire point of the HK theorem was that the relationship was bijective

Manishearth

@ricj oh, I have no clue what the question is asking. I just advertised it for the guy.

F'x

ah, I see the difference: HK states that there is bijection between Vext and "any density that is the ground state density of a Vext"

hum… tricky

anyway, gotta get some coffee and then back to reading

ciao!

Richard Terrett

@Fx I believe that's what this book si trying to say, however it indicates that the mapping of wavefunctions to densities is surjective

F'x

8:59 AM

@RichardTerrett well, a density can always be constructed from a set of wavefunctions, so that's the easiest assertion, I think (or am I wrong?)

F'x

9:39 AM

regarding periodic vs. periodic I should say I'm completely open to it being to it being migrated to English.SE if it's deemed off-topic here

Manishearth

@Fx Yeah, it's actually good to ask borderline questions now I guess so that we can determine allowed-questions

pɪə looks like an upside down "eid"

(that's what I read it as first)

A possible answer could be "nobody cares". Appending "acid" to the word removes all doubt

(with professional chemists)

Students, on the other hand, will be perennially confused by this

Richard Terrett

hang on, i'm penning an interesting (imho) answer

Manishearth

We once had that in a question paper of ours, nobody realised that it was per-iodic

I have a speculative answer

F'x

0

Q: What is the difference between melting and dissolving?

What is the difference between melting and dissolving? I am looking some general features. The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (ethanol) just below(or at the) melting point of ice, or similar phenomena. I am now assuming that...

solvents solubility melting-point phase

What should we do about the above? To me, it's too broad/general reference

Manishearth

@Fx One sec

Stack Exchange

9:51 AM

0

Q: Should one pronounce “periodic” the same in “periodic acid” and “periodic table”?

In “periodic table”, the adjective is related to the noun period, and comes from Ancient Greek περίοδος through French périodique. In “periodic acid”, it is formed from the prefix per- and iodic (like peroxide and permanganate). Wiktionary lists their respective UK pronounciations of as /pɪə(ɹ)....

pronounciation

1

Q: How are turbostratic graphite phases formed?

Turbostratic graphite is graphite in which there is quenched rotational disalignment between adjacent graphene sheets, i.e. one sheet is rotated with respect to its neighbor. I suppose this could be considered a crystallographic defect of sorts. How do these turbostratic layers form, and can they...

graphite solid-state-chemistry

0

Q: What is the difference between melting and dissolving?

What is the difference between melting and dissolving? I am looking some general features. The answer should be adaptable to the melting/dissolving of ice cube (water) in a class of pure alcohol (ethanol) just below(or at the) melting point of ice, or similar phenomena. I am now assuming that...

solvents solubility melting-point phase

Manishearth

@StackExchange Shut up

:P

:4531265 I've always wanted to do that! (I have ownership of the Phy.SE chat room but there's nothing weird to do there)

You mods get all sorts of fun powers ;-)

@Fx I think it's slightly broad since dissolution covers multiple mechanisms

F'x

@Manishearth I've added a comment, and I'll vote to close unless the question is edited

Manishearth

@Fx You can VTC beforehand and reopen when its improved--that's how VTC is supposed to be used. But without pro-tems around, I think we shouldn't do such shenanigans yet (reopening will take more time)

Richard Terrett

now i'm reading the name of this room as 'per-iodic table'

Manishearth

@RichardTerrett Room name changed to "The $\ce{HIO4}$ Table"

Richard Terrett

10:03 AM

heh

2

Q: How did the Swedish word "fartlek" make it to the English language running vocabulary?

This is a question originally from Fitocracy by ivh: Btw, anybody know how come that the Swedish word "fartlek" made it into English running lingo?

etymology loan-words

I love it

F'x

@Manishearth well, closing will probably take a lot of time too :)

we have 7 users able to cast close votes so far

Manishearth

@Fx Yep

Richard Terrett

I just noticed that I've had an arduino plugged in here for the past 2 days, flashing LEDs in sequence

Richard Terrett

10:29 AM

Well, it looks like the group is getting ADF-BAND :)

@Fx I forget if I asked - are you acquainted with BigDFT?

Manishearth

@Fx We can have a chat room dedicated to cleanup--and force all 7 users to stay in the room or else ;-)

Richard Terrett

cleanup?

oh right

F'x

@RichardTerrett no, I'm not

Richard Terrett

Hopefully this beta will pick up now that it's public. IT MUST LIVE.

@Fx ah okay. I'm dabbling with it. wavelet DFT code, optionally cuda accelerated

F'x

in terms of quantum chemistry code, I use (or have used) CPMD, CP2K, SIESTA, CRYSTAL, Gaussian and DMol…

Richard Terrett

10:42 AM

@Fx Noted :D

Manishearth

10:54 AM

@Fx You may want to also add meta.chem.SE to the site feeds

Richard Terrett

i had no idea ICP-MS existed

Stack Exchange

F'x has made a change to the feeds posted into this room

Manishearth

@StackExchange Thanks :)

F'x

bounty-time!

Richard Terrett

@Fx I see you're blowing your rep on bounties :D

ah, like you said

F'x

11:03 AM

@RichardTerrett well, they won't let me get any real money from it anyway, will they? :)

I don't think the extra rep does much to encourage people to write an answer, but it does draw attention to the question

Manishearth

@Fx Yeah, a big flashing blue thingy does tend to catch your eye ;-)

OK, not flashing

You're probably going to be a pro-tem here (high rep, good meta participation, already a mod, etc), so I guess rep wrt privileges won't matter to you anymore :)

F'x

@Manishearth one important factor is available time, though :(

Manishearth

Though we still have a few weeks(I think) so could you blow up your rep later ? We do need some high-reps out here till then

@Fx Oh, you're not going to run for election? (I was planning on nominating you)

:(

F'x

@Manishearth there's not election until we're out of beta

Manishearth

@Fx Pro tem

Oh, that's not an election?

Richard Terrett

11:07 AM

what does pro tem mean?

Manishearth

I know it's not under /election

F'x

@Manishearth now, that's a team nomination

@RichardTerrett pro tempore

on a temporary basis, until moderators are elected after the site graduates

Manishearth

@RichardTerrett For beta sites, you have pro tem mods. They aren't permanent (there are full fledged elections after the site graduates)

Richard Terrett

ahhhh

Manishearth

They have full powers though

F'x

11:08 AM

I meant to say: pro tem mods are chosen by the SE team

Manishearth

Blog - Stack Exchange: Moderator Pro Tempore

Robert Cartaino on July 27, 2010

There’s a bit of a leadership vacuum inside the new Stack Exchange communities in public beta. We’ve put a lot of responsibility on each group to take ownership of their own site. The Stack Exchange team can act as guide, but we don’t always have the domain knowledge to understand the needs of each group. As the Network expands, this stretches our ability to assure that each community’s issues are properly addressed.

That’s why I am in the process of identifying and organizing a team of provisional Moderators from within each community (about three per site, starti …

@Fx Wait, the last section in the meta post says self-noms are encouraged

o_0

F'x

@Manishearth yes, self nominations are okay… moderators shan't shy anyway!

Manishearth

@Fx Aah, but I can't nominate you you mean to say :)

F'x

@Manishearth I'll make my mind when the time comes

Manishearth

No wait, there's a bit on 3rd party nom

F'x

11:11 AM

@Manishearth anything is fine… self or third-party…

Manishearth

Oh, I see what you mean--the community voting is not the deciding factor, the final decision is in SE's hands

So it's not an "election" per se, more of a nominate-and-the-gods-will-choose

F'x

@Manishearth indeed

Richard Terrett

looks tasty

F'x

@RichardTerrett yummy sandwich

Manishearth

@RichardTerrett Just what I was about to say :)

F'x

11:20 AM

don't do that, it's past noon here already and I still haven't had lunch!

Richard Terrett

top is cherry, bottom is blueberry

Manishearth

@Fx Unless, of course, it's a nuclear sandwich :)

23 hours ago, by Richard Terrett

@Manishearth - Uranocene, the nuclear sandwich: http://en.wikipedia.org/wiki/Uranocene

F'x

okay, gone for lunch!

Manishearth

@Fx cya!

Mats Granvik

11:49 AM

I am surprised by how little activity there seems to be on chemistry stackexchange. Are chemists not used to computers and internet forums or do they simply have other things to do like work?

Manishearth

@MatsGranvik They have to eat lunch

"They" being our most active user (who accounts for half our activity)

;-)

@MatsGranvik Seriously though, it's just out of public beta. Let the word get out. Do some advertising yourself :)

Mats Granvik

Sofar I have only mentioned this site to 2 other persons I know.

Manishearth

@MatsGranvik Moar people!

@MatsGranvik I referred it to totally 5 (of which two didn't use the a51 link)

Out of those, we have one guy writing loooong answers (as he usually does on Phy.SE), and another user who has posted one question and plans to post one more

Another one plans to ask once he thinks up a question :P

The remaining two, well, i dunno

Mats Granvik

ok, I see :)

Manishearth

Basically not all the guys you refer will be active. So refer moar moar people!

@MatsGranvik And ask more questions!

F'x

11:57 AM

@Manishearth hey, I heard that!

Manishearth

@Fx Well, you are, aren't you?

area51.stackexchange.com/proposals/…

Activity includes edits

F'x

@Manishearth 10 questions out of 98

Manishearth

You have double everyone's rep (though after the bounties I think I'm an exception to that)

50 secs ago, by Manishearth

Activity includes edits

@Fx OK, fine, a tenth of the activity.

F'x

well, I'll try harder to let others answer

Manishearth

Hmm..

F'x

12:02 PM

but I'll continue to edit a lot, because that's one way we can directly increase quality

Manishearth

@Fx Yep :)

Manishearth

12:23 PM

/leaves

rcollyer

1:04 PM

@RichardTerrett That is lovely. What was used to generate it?

Anil

Hi, can we have a question in a such a manner that users can append the answer? Like list of compounds which does A,B, etc

rcollyer

@Anil As I am not a regular here, I don't know. But, in general big-list types of questions are generally discouraged. In particular, finding a good answer in the inevitable long list of ones is difficult. As an alternative, sometimes the community will opt to maintain an answer that summarizes the thread, but this is often out of date quickly. Additionally, for that topic, in particular, the list would be particularly lengthy, and potentially ever growing.

Anil

@rcollyer I was referring to chemistry related questions like red-ox reagents. Can we have it main forum or this particular question (having a long list) in meta?

rcollyer

@Anil I understood what you were asking, and I was trying to explain why they're generally frowned upon. That said, some sites do fine with them, but they're careful with them. I would ask if that is a permissible question on meta, that way you can determine the community's opinion.

Anil

1:26 PM

@rcollyer As you said, i am planning to post it on meta

Manishearth

2:00 PM

pokes head in

nobody there

Andrew

@Manishearth hi

Manishearth

leaves

Oh

scratch that

Anything exciting happened?

Andrew

lol not with me

trying to catch up on all the questions, and generally feeling inadequate about my chemistry knowledge :P

Manishearth

Same here

"all the questions" that's not much :(

Andrew

2:17 PM

yeah that's true

Anil

@Manishearth, I have added comment to your reply. i was referring to what rcollyer has pointed out

LordStryker

3:54 PM

@Fx I'm still mulling over the Pulay force thing. Honestly it boils down to this. Whether or not Pulay forces are difficult to compute is really moot. The fact that you do not have to evaluate them does indeed save time since they would need to be computed once every iteration. This adds up in expense over time.

@Fx The 'difficulty' part is moot because I've asked around and people have varying opinions about what 'difficult' really means. So in summary, I'm going to just say that they are not difficult to compute (having a computer do it).

F'x

7:24 PM

@LordStryker what I mean is: given that you have already calculated forces and integral overlaps, do they reduce to a series of matrix calculations, do they involve matrix inversion (probably not) or do they require the calculation of new integrals?

and I've edited my question to make it clearer

F'x

9:27 PM

@All: please give your opinion in meta or in chat about what our threshold should be for "too easy" questions

and to help with the theory, I give you an example… in your opinion, how does the following question fit into our site?

1

Q: Which desolvation reactions are endothermic?

Are there reactions like $X(s) + n Y(l) \to X \centerdot Y_n(l)$ that are endothermic? What are X and Y then? The material X should also be soluble to material Y.

physical-chemistry solvents solubility energy

Andrew

@Fx, I agree, a little too easy

F'x

9:47 PM

also, you can queue edit suggestions (posts or tag wikis) and I'll try to review them regularly enough… if the edit queue fills, ping me here (until I'm no longer the only person with enough rep to review)

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