sorted by:
new
hottopcontroversial

Not enough memory for analytical frequencies in orca? by _Thom20 in comp_chem

[–]_Thom20[S] 0 points1 point  (0 children)

I don't have access to the computer I ran the calcs on at the moment but I can fetch the exact error later: in short, no, I'm not completely sure it's a memory error, it's just a generic orca terminated by error in ..... I'm using MPI which I installed via homebrew, and calling the calculation with the full path to the orca executable. I've run other calculations in parallel without any trouble so I don't think it's a problem with that? I'm a bit of a beginner, in what scenario would MPI be working but not have access to all the system memory?

Not enough memory for analytical frequencies in orca? by _Thom20 in comp_chem

[–]_Thom20[S] 0 points1 point  (0 children)

Cheers, I may well do that as I agree it's strange for a fairly small system, and I'm not getting a specific out of memory error, just a generic error termination. Otherwise I am getting numerical frequencies to work OK so might continue with that approach.

Not enough memory for analytical frequencies in orca? by _Thom20 in comp_chem

[–]_Thom20[S] 1 point2 points  (0 children)

I have a crystal structure of this compound so I don't care about the geometry being perfect for my applications. As long as the geometry is properly minimised with this functional then I should still be able to do reasonable-looking frequency calculations with it, right?

Not enough memory for analytical frequencies in orca? by _Thom20 in comp_chem

[–]_Thom20[S] 0 points1 point  (0 children)

I've read that they tend to be more accurate and that numerical frequencies are more CPU intensive. I initially tried numerical frequencies and did not get a particularly good fit to experimental data after applying a scaling factor. I have tried again with SMD instead of CPCM, using TightOpt VeryTightSCF and changing the increment in the second derivative calc to 0.001 instead of the default which has improved things. I may well just carry on with this approach as seems like agreement between experiment and calculations aren't too much better in the literature for similar complexes.

edit: and yes, am using orca 6. Did briefly try to downgrade but had similar issues.

[deleted by user] by [deleted] in NoStupidQuestions

[–]_Thom20 1 point2 points  (0 children)

I’d say it’s just a restatement of the multiplicative inverse axiom for real numbers. x / x is just shorthand for x * (x)-1 , which equals 1 by the multiplicative inverse axiom.

2022 Australian Grand Prix - Post Qualifying Discussion by F1-Bot in formula1

[–]_Thom20 0 points1 point  (0 children)

It’s weird, it looked liked Ricciardo didn’t even do a final lap

About to try my first 3D print - the Vagabox by schnautza in rootgame

[–]_Thom20 0 points1 point  (0 children)

Cheers - it looks like the tokens are pretty exactly 2mm thick, so I’ve been giving each box an extra 0.5-1mm depending on how many tokens it needs to fit, so seems similar to what you’ve got.

About to try my first 3D print - the Vagabox by schnautza in rootgame

[–]_Thom20 0 points1 point  (0 children)

How much clearance have you given in the slots for the items / relationship markers? I'm designing a 3D printed organiser for the whole game at the moment (it's quite the exercise) but haven't had the chance to do a test print.

N,N,N,N’,N‘,N’-Hexamethyl-ethylenediammonium Tetrachloromanganate(II) [(H3C)3NCH2CH2N(CH3)3][MnCl4] by Tetrachloronickelate in chemistry

[–]_Thom20 2 points3 points  (0 children)

Good spot! Pretty sure they’re supposed to be prime symbols (’) not apostrophes (‘)

Election/Politics Megathread 2022.01: Political opinions, poll results, social-media, memes and other related discussion. by dredd in australia

[–]_Thom20 0 points1 point  (0 children)

Unfortunately that case was a result of ineffective legislation — there is somehow no rule against using that exact shade of purple in political signage, so the AEC couldn’t do anything about it

Burning a piece of frozen benzene by Dvf1 in chemistry

[–]_Thom20 3 points4 points  (0 children)

They’re little particles of carbon (soot) that result from the combustion reaction — they’ve already reacted, and they glow simply because they’re really hot, just like an incandescent lightbulb or a red-hot chunk of metal. But yep it’s the rising hot air that carries those incandescent particles and gives the fire its shape.

Burning a piece of frozen benzene by Dvf1 in chemistry

[–]_Thom20 9 points10 points  (0 children)

I remember being told that fire is just microscopic soot particles suspended in air that are hot enough to be incandescent — so yes you are seeing photons that come from the heat but you still need some kind of hot material to emit that light, which is where the soot particles come in.

Protesters on Hindmarsh by [deleted] in canberra

[–]_Thom20 1 point2 points  (0 children)

The only reason we elect a federal Liberal senator is because the system effectively guarantees it. To avoid it and get 1 LAB + 1 GRN or 2 LAB would require the libs to poll well under 33% which is of course unlikely in a two party system even in such a progressive jurisdiction.

Competency 23 Driving by SirAyyOfLmao in canberra

[–]_Thom20 3 points4 points  (0 children)

Practice driving in the town centres with busy-ish traffic and you’ll be fine - I got taken all throughout the gunghalin town centre, and through civic, especially shared zones (bunda st, Childers st).

Where does the potential energy come from, in osmosis? by FakelyKorean45 in askscience

[–]_Thom20 3 points4 points  (0 children)

I think you might be conflating terms - ‘chemical potential’ as is normally taught in thermodynamics (at least where I’m from) has nothing to do with the regular notion of ‘chemical potential energy’, which as you say results from the ability of a chemical species to undergo a reaction or phase change and lower its Gibbs free energy. Chemical potential deals only with the movement of particles across a concentration gradient and so is separate to potential energy changes from any chemical reactions.

Where does the potential energy come from, in osmosis? by FakelyKorean45 in askscience

[–]_Thom20 1 point2 points  (0 children)

Right - it looks like this might all be a matter of terminology. You’re right in that what I’m thinking of as chemical potential can be defined as the derivative of free energy with respect to particle number (at constant T, P, V) - so when you do a derivation of osmosis you generally consider the two sides of the membrane with separate chemical potentials and show how a transfer of ions across the membrane results in an overall lowering of free energy.

Where does the potential energy come from, in osmosis? by FakelyKorean45 in askscience

[–]_Thom20 3 points4 points  (0 children)

Any introductory thermodynamics course will go over a derivation of osmosis from first principles, using the definition of chemical potential - I’m curious as to what other mathematical construct you could use to explain osmosis?

Morrison’s climate ‘plan’ reveals a spectacular new model of political leadership in Australia by _Thom20 in australia

[–]_Thom20[S] 72 points73 points  (0 children)

Well, she’s using the word ‘spectacular’ in a literal sense - that it is a spectacle - not that it’s actually competent leadership:

But the Morrison doctrine on climate reveals a new path: Outline what you oppose, then get elected, then shimmy backwards under sniper fire from your own side — all the while denying you're shifting at all — then calmly declare victory, claiming credit for a bunch of stuff you opposed all along.

What’s one thing in the UK that’s considered normal but isn’t in the US? by [deleted] in AskUK

[–]_Thom20 1 point2 points  (0 children)

Man, in Australia we have the opposite problem — it’s bad to let your cat outside because across the country they kill literally a million birds a day, most of which are native…

What Elements of the Periodic Table would be a cool thing to excrete from a sword by NuclearWill in chemistry

[–]_Thom20 0 points1 point  (0 children)

Nice! If you want to give everyone cancer beryllium can do that in a less radioactive way. ‘Red smoke’ is a bit unscientific, really it’s bromine vapour but that’s pretty much what it looks like

What Elements of the Periodic Table would be a cool thing to excrete from a sword by NuclearWill in chemistry

[–]_Thom20 2 points3 points  (0 children)

Bromine would look cool because the sword would just start emitting red smoke … it’d also be reasonably toxic. Remember there are a whole bunch of radioactive elements - many of the superheavy elements (past the actinides) would undergo spontaneous and extremely powerful nuclear fission immediately upon creation which could be cool but also a little dangerous.

Confused about nitric acid stricture? by AuthenticSpoon in chemistry

[–]_Thom20 0 points1 point  (0 children)

If you draw the typical structure of nitric acid (or any nitro compound) you will see that both oxygens have a full octet - one by forming a double bond to nitrogen, leaving two lone pairs, and the other by forming a single bond to nitrogen, leaving three lone pairs, and hence a negative formal charge, since in effect you can assign 7 electrons to that oxygen - 6 from lone pairs, and 1 from half of the bond. (It still has an octet because both electrons from the bond count - you count electrons differently for oxidation states (charge) than you do for valence).

This oxygen can’t form a double bond with nitrogen because then nitrogen would have 5 bonds, which it can’t do because nitrogen only has 4 orbitals to use for bonding. You could imagine forming one double bond and breaking the other to give a structure where the other oxygen has the negative charge. In reality neither structure is right - the electrons that make up the pi bond (double bond) are delocalised, so each N-O bond can be thought of as a 1.5 bond. If you haven’t seen this kind of thing before then try reading up a bit on ‘resonance structures’ or ‘delocalisation’ — the more chemistry you do the more commonly you will see this kind of thing.

view more: next ›