I fully agree with Phil!
Dirk.
Am 26.02.10 10:31, schrieb Phil Evans:
... and positive difference density should be red not green :-)
Phil
On 26 Feb 2010, at 09:22, Tim Gruene wrote:
Dear all,
Gerard Kleywegt, Bernhard Rupp and also John Helliwell explained to me that the
unit of f' and friends is indeed meant to be electrons as in the elementary
particle and not electrons as charge unit as in eV.
Personally I find this very irritating and such things should be avoided - the
formulae wouldn't change by using e (as in charge) as unit and adding a
minus-sign. I should remember that a charge density map has negated signs
compared to an electron density map.
But I admit this is my personal view and might start a lengthy discussion about
units as - if I remember correctly - we had on this board not long ago.
It's just like my disliking that negative charge seems red for chemists and
positive charge seems blue.
Cheers, Tim
On Fri, Feb 26, 2010 at 10:01:45AM +0100, Gerard DVD Kleywegt wrote:
Hi Tim,
Maybe it's too early in the day for me, but why can't electrons be a
unit? You seem to be confusing physical (in-)divisibility of an entity
with the symbolic use of fractions of that entity in calculations. We can
speak of the average number of cows per acre of land without having to
cut up cows into small pieces (although I love a good steak as much as
the next person - and probably a lot more than that), or the average
number of people on a plane without having to remove some limbs of a
particular person to represent that number (although amputation of my
legs would make my journeys a lot more comfortable in terms of legroom).
--dvd
Disclaimer: this answer does not involve any (mention of) CCP4 software.
Mea culpa.
On Fri, 26 Feb 2010, Tim Gruene wrote:
Dear all,
I just stumbled across the question about what is the unit of f' and
f''. The
first couple of hits from ixquick.com claim it was e^-. Since e^- is
not a unit
but symbolises an elemtary particle (of which fractions are considered
non-existent), I was wondering whether the unit of f, f', and f'' is
actually e
(a positive charge!) and the value of f^0 of Fe at its K-edge was
actually 26e
or -26e - see e.g. Table 1 in
http://www.ccp4.ac.uk/courses/proceedings/1997/j_smith/main.html
Cheers, Tim
--
Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen
GPG Key ID = A46BEE1A
Best wishes,
--Gerard
******************************************************************
Gerard J. Kleywegt
Dept. of Cell& Molecular Biology University of Uppsala
Biomedical Centre Box 596
SE-751 24 Uppsala SWEDEN
http://xray.bmc.uu.se/gerard/ mailto:[email protected]
******************************************************************
The opinions in this message are fictional. Any similarity
to actual opinions, living or dead, is purely coincidental.
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--
--
Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen
GPG Key ID = A46BEE1A
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Dirk Kostrewa
Gene Center, A 5.07
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