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:[log in to unmask]
>>> ******************************************************************
>>> The opinions in this message are fictional. Any similarity
>>> to actual opinions, living or dead, is purely coincidental.
>>> ******************************************************************
>>>
>> --
>> --
>> Tim Gruene
>> Institut fuer anorganische Chemie
>> Tammannstr. 4
>> D-37077 Goettingen
>>
>> GPG Key ID = A46BEE1A
>>
>>
--
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