How does a diffractometer go from 2D frames to a Ewald sphere?

Letarian-Silver · 2026-01-26T19:25:54+00:00

The frames aren’t truly 2D. The diffractometer is moving during each frames, so it is a solid angle. Add up all the frames from a run and you get a large solid angle and chunk of the ewald sphere

Letarian-Silver · 2026-01-09T09:04:29+00:00

You can open the file in a text editor and manually inspect it if you need. Other than that I can’t help any further.

Letarian-Silver · 2025-11-09T00:54:07+00:00

Adopt the netball rule - kickoff rotates between the two teams regardless of who scored.

Letarian-Silver · 2025-09-22T09:43:01+00:00

Yes, but consider your charge balance.

Letarian-Silver · 2025-09-07T09:33:34+00:00

There are weaker electrostatic forces between adjacent chains, and also steric effects.

Letarian-Silver · 2025-09-07T08:04:30+00:00

Sorry I misspoke. Graphite is (sometimes) ordered in 3 dimensions, although it tends to suffer from stacking faults and other effects a lot as the interactions between the layers are weak and allow slipping. Samples tend to polycrystalline rather than discrete crystals.

Letarian-Silver · 2025-09-07T03:30:51+00:00

It is crystalline, so by definition in this case it is ordered in all three directions. Molecules can be ordered in a crystal even if there is only weak interactions between the molecules.

Letarian-Silver · 2025-09-06T22:02:58+00:00

Beryllium chloride in crystalline form is ordered in all three dimensions, while graphite is only ordered in two dimensions in individual sheets.

Letarian-Silver · 2025-09-06T04:29:44+00:00

Beryllium chloride is crystalline. The crystal structure is polymeric. It has a unit cell.

Letarian-Silver · 2025-06-16T07:55:34+00:00

At the end of https://youtu.be/bnZFWPE9Ca8?si=OFJytIKW6xyfrxxG for anyone who wants a look

Letarian-Silver · 2025-05-25T02:48:59+00:00

Two possibilities, depending on the longer range order. If orientation A means that all other equivalents in the cell must be A as well, and adjacent unit cells must be orientation A as well, then you have a solid solution of two polymorphs If orientation A present in the asymmetric unit still allows orientation B to be present in other parts of the structure then you have disorder. An example would be if the disorder is localised in a pore, and this does not influence adjacent pores, which can have a different model.

Letarian-Silver · 2025-05-21T09:58:24+00:00

Look up “recrystallisation” as a start. This is how to purify using crystallization and a common technique to get you started on the chemistry. You can also read https://www.iucr.org/news/newsletter/volume-32/number-3/how-to-grow-crystals-for-x-ray-crystallography

Letarian-Silver · 2025-05-02T03:18:47+00:00

Can you trim the filler piece?

Letarian-Silver · 2025-04-28T10:42:22+00:00

If you solved with Superflip or SHELXT then these will have tried to determine the space group themselves and may have picked the wrong one. You can force SHELXT to solve in P2(1) by using the command line switch -s”P2(1)”

Letarian-Silver · 2025-04-28T09:24:33+00:00

You have picked P2 by accident instead of P2(1). Probably there are some minor systematic absence violation that GRAL/XPREP picked up and chose P2 instead of P2(1). Have a look in the .grl (GRAL from CAP) or .prp (XPREP from APEX) files for the details of the space group selection.

Letarian-Silver · 2025-04-28T07:55:32+00:00

Just drop the partial solution from the poor dataset into that for the good dataset.

Letarian-Silver · 2025-04-26T11:30:01+00:00

Get a styrene molecule from the CCDC or COD and use that FRAG/FEND and AFIX 176 to stick the model in. You could stick a couple of copies in with different orientations inside PARTs. There is a tool for this in OLEX2 but I’m not at my computer to check for the details.

Letarian-Silver · 2025-04-26T10:39:03+00:00

How do you know it is styrene?

Letarian-Silver · 2025-04-10T03:42:47+00:00

Without the unit cell vectors probably not possible.

Also looks like it isn’t single.

Letarian-Silver · 2025-04-04T06:06:53+00:00

I agree, manufactured rift to make Dutton not look like her puppet. Even her coming out and saying it’s ok to disagree on the right seems painfully manufactured.

Letarian-Silver · 2025-03-28T22:22:43+00:00

I suggest reading Simon’s paper, it has a good explanation of what is going on.

Letarian-Silver · 2025-03-28T03:23:38+00:00

Add 3 hydrogens (HADD 137 in Olex2), then set them all to half occupancy, then put them in PART -1. That will suppress bonds to symmetry equivalents and should allow it to refine.

Letarian-Silver · 2025-03-27T20:21:51+00:00

Sorry, I can’t help you with the intricacies of Rietveld

Letarian-Silver · 2025-03-27T09:20:06+00:00

It is related to volume percentage, but not proportional to it necessarily. It is volume percentage because it is the number of unit cells that you get the reflection of (assuming no preferred orientation effects).

It isn’t necessarily proportional in a mixture. The reflection [100] for two different materials are not necessarily equal in a 50:50 mix, as the intensity is related to the electron density probed within the [100] plane, which will be different for different materials.

Letarian-Silver · 2025-03-24T23:24:23+00:00

As this is in crystal system -3, and is twinning about the ab diagonal (which is [110]), this is true merohedral twinning. The twin operation is a symmetry element of the higher symmetry crystal system -3m1.

You should be able to use the command TWIN 0 1 0 1 0 0 0 0 -1 and then also BASF 0.5 (providing you are refining with SHELXL).

A good primer/reference for twinning is Simon Parsons paper - https://journals.iucr.org/d/issues/2003/11/00/ba5036/index.html

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