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### Topic: what does "e" stand for?  (Read 18519 times)

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#### zmasterflex

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##### what does "e" stand for?
« on: June 20, 2013, 09:16:23 AM »
Hi. I'm an undergraduate student volunteering in research and I'm trying to get some unsupervised work done while my instructor is on vacation. We are working with the correlations between cohesive energies as they relate to madelung constants in nanotubes. The basic gist (as far as I understand) is that there is a linear relationship with an r^2~1 for the tubes we have computed. I'm trying to calculate charges for the individual ions but the derived equation I was given doesn't seem to be accurate because other calculations which use calculated charges are way off. I'm looking around at other papers printed on this topic and I see that columbic energy=(MC*z*z)/r where MC=madelung constant, z is charge and r is distance. Another paper demonstrates that the slope (of cohesive energy vs. MC)=(-e^2*z^2)/r. What does the "e" stand for in the second equation? Is more info needed? thanks

#### curiouscat

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##### Re: what does "e" stand for?
« Reply #1 on: June 20, 2013, 09:50:39 AM »
Electron charge?

#### zmasterflex

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##### Re: what does "e" stand for?
« Reply #2 on: June 20, 2013, 11:34:20 AM »
z is charge. Im hoping to isolate z because I have the slope and distance already. All I need is "e". Is it rude or unrealistic to post the link to the paper up here? thanks

#### Corribus

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##### Re: what does "e" stand for?
« Reply #3 on: June 20, 2013, 12:29:56 PM »
Most papers will define their variables somewhere in the text.  Just throwing out an equation at us and hoping we can tell you what the variables are is a little bit wishful thinking.  Curiouscat is right in that e is almost always the electronic base charge, but especially in older papers today's conventions weren't always in practice.

Maybe you can provide us the reference and we can look at the source material.

(Don't post the actual paper - this is against the law.  But you can post the link to the paper at the journal's website and people who have legal access will be able to access it.  Or just provide the citation.)
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#### Yggdrasil

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##### Re: what does "e" stand for?
« Reply #4 on: June 20, 2013, 02:34:31 PM »
z is charge. Im hoping to isolate z because I have the slope and distance already. All I need is "e". Is it rude or unrealistic to post the link to the paper up here? thanks

z is likely charge in the way chemists usually think of charge (+1, +2, -1, -2, etc.).  e is probably the elementary charge, in other words, the charge of the electron in coulombs.

#### curiouscat

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##### Re: what does "e" stand for?
« Reply #5 on: June 20, 2013, 03:39:04 PM »

z is likely charge in the way chemists usually think of charge (+1, +2, -1, -2, etc.).  e is probably the elementary charge, in other words, the charge of the electron in coulombs.

Exactly how I'd interpret it.

#### curiouscat

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##### Re: what does "e" stand for?
« Reply #6 on: June 20, 2013, 03:41:53 PM »

(Don't post the actual paper - this is against the law.  But you can post the link to the paper at the journal's website and people who have legal access will be able to access it.  Or just provide the citation.)

I think, even posting a page, or a few paragraphs or a screenshot would be legally OK, withing the "Fair Use" exception. (though not sure if Chemical Forums has a less permissive policy)

Copy pasting a few paragraphs (with citation) is also almost surely kosher.

#### Borek

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##### Re: what does "e" stand for?
« Reply #7 on: June 20, 2013, 04:13:44 PM »
Copy pasting a few paragraphs (with citation) is also almost surely kosher.

Yep. Just don't quote whole paper, only relevant part.
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#### Dan

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##### Re: what does "e" stand for?
« Reply #8 on: June 20, 2013, 04:22:45 PM »
Is it rude or unrealistic to post the link to the paper up here?

You can post a link to the paper at the publisher's website (where purchase/subscription might be required to read it) - the problem is when you post a link to (or upload) a copy of a paper that is not open access (copyright infringement).

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#### Wastrel

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##### Re: what does "e" stand for?
« Reply #9 on: June 21, 2013, 02:47:56 PM »
Probably inverse natural logarithm.

#### Borek

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##### Re: what does "e" stand for?
« Reply #10 on: June 21, 2013, 04:29:03 PM »
Probably inverse natural logarithm.

Highly doubtful. While you are right e is a base for natural logarithms, in this context - z2e2/r - it looks like (ze)2/r which is just an ugly way of expressing q2/r. For me that strongly suggests Yggdrasil is right.
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#### Wastrel

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##### Re: what does "e" stand for?
« Reply #11 on: June 22, 2013, 07:42:25 AM »
I read the equation wrong the first time and it didn't click, that does look most likely.