The lambda = 2d is a pure mathematical evidence that the photon is
not a mathematical point moving with a certain speed, but a particle
with a certain geometrical dimension.
Than the photon is massless just regarding an origin moving with the c
speed to the Universe (that may finally appear a
Stephen and Bob,
The issue very simply is once you define a site as 'x,y,z', are -x, -y, and -z
all used in the definition of other sites in the group? If so the origin has
been defined. If not the origin is arbitrary in those directions lacking a minus
sign on their operator. This m
Stephen,
Whether the space group is centrosymmetric or not isn't the issue. The question is
whether it is polar or not. P2/n is not polar (i.e. origin defined relative to some
symmetry element) but P2 is polar (i.e y coordinate not chosen relative to a symmetry
element).
Bob Von D
Dear Robert B.Von Dreele
Thank you for your explanation.
Therefore GSAS could do the origin fixing for us when the space group is not
centrosymmetric. Can I boardly say that?
regards,
stephen
. They should always be the same.
Bob
From: Peter Zavalij [mailto:[EMAIL PROTECTED]
Sent: Wed 3/31/2004 10:37 AM
To: [EMAIL PROTECTED]
Bob,
Thank you for the clarification. I never had doubts that GSAS handles fixed origin
issue properly but also never understand h
---
-Original Message-From: Andreas Leineweber
[mailto:[EMAIL PROTECTED]Sent: Wednesday, March 31, 2004 11:09
AMTo: [EMAIL PROTECTED]Subject: Re: Defining the origin of
P2/nThis problem can actually quite simply be solved
without tables:There is the old rule (which crystrallographers a
ded.
I might also note that all of this is based on the use of keyboards in
general
use in English speaking countries. And I did have no information concerning
what
you might get using other keyboards.
Now for P2/n is a centric space group for which there, in my mind, there
exists
no reasonable o
ular to a glide plane, so it does have fixed
points (unlike e.g. R3c).
Best regards,
Magnus H. Sørby
-Opprinnelig melding-
Fra: Kurt Leinenweber [mailto:[EMAIL PROTECTED]]
Sendt: 31. mars 2004 08:55
Til: [EMAIL PROTECTED]
Emne: Defining the origin of P2/n
Stephen,
I think that P2
PROTECTED]
Sent: Wednesday, March 31, 2004 8:17 AM
To: [EMAIL PROTECTED]
Dear Stephen (& others),
I know there have been a number of replies to this since P2/n does have an
inversion center which is positioned at the unit cell origin. However, if
the space group is Pn (or P2) then the location of
and Kurt,
P2/n has a 2-fold axis perpendicular to a glide plane, so it does have fixed
points (unlike e.g. R3c).
Best regards,
Magnus H. Sørby
> -Opprinnelig melding-
> Fra: Kurt Leinenweber [mailto:[EMAIL PROTECTED]
> Sendt: 31. mars 2004 08:55
> Til: [EMAIL PROTECTED]
>
Obviously. I was talking about fixing the origin when it is not fixed by symmetry.
By the way, GSAS when generate symmetry from space group symbol provide information
about the origin.
If the origin is not fixed by symmetry is it clearly stated:
For example for P2 "The location of the orig
Peter Zavalij wrote:
>
> Bob,
> Thank you for the clarification. I never had doubts that GSAS handles fixed origin
> issue properly but also never understand how it
> is done. This way has one big advantage over user fixed origin -- it yields standard
> uncertainties for all a
doubts that GSAS handles fixed origin
issue properly but also never understand how it
PZ> is done. This way has one big advantage over user fixed origin -- it yields
standard uncertainties for all atoms and therefore for
PZ> all distances, etc.
PZ> Peter Zavalij
PZ> -Original Mes
Bob,
Thank you for the clarification. I never had doubts that GSAS handles fixed origin
issue properly but also never understand how it
is done. This way has one big advantage over user fixed origin -- it yields standard
uncertainties for all atoms and therefore for
all distances, etc.
Peter
aking countries. And I did have no information concerning what
you might get using other keyboards.
Now for P2/n is a centric space group for which there, in my mind, there exists
no reasonable origin choice that the 1bar site. Therefore the software would
always choose that for the origin of the unit cell.
Allen C. Larson
Dear Stephen (& others),
I know there have been a number of replies to this since P2/n does have an inversion
center which is positioned at the unit cell origin. However, if the space group is Pn
(or P2) then the location of the origin is arbitrary on one or more axes. GSAS does
"auto
er this from refining the
> structure of high pressure FeTiO3 which had space group R3c.
>
- Kurt
yes, i do think this centric space group does not need any origin fixing.
And this first atom is not in special position at all. Thank a lot.
stephen
CTED]
> Emne: Defining the origin of P2/n
>
>
> Stephen,
>
> I think that P2/n has no fixed points, and in order to keep the whole
> structure from shifting along the c-axis, one of the atoms has to be
> arbitrarily fixed. GSAS automatically fixes the first atom
> z-p
Stephen,
I think that P2/n has no fixed points, and in order to keep the whole
structure from shifting along the c-axis, one of the atoms has to be
arbitrarily fixed. GSAS automatically fixes the first atom z-parameter (was
your atom on the 2-fold symmetry axis?). I remember this from refining t
Dear Rietvelders,
I used GSAS to refine my structure in P2/n, however the program automatically
fixed the the XYZ positions of the first atom during refinement. To my
surprise, this atom is not seen in the "fixed atom list" in the atom parameters
menu of GSAS.
Please advise and many thanks,
step
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