iucr

commissions

principles
aperiodic crystals
biological macromolecules
quantum crystallography
crystal growth and characterization of materials
crystallographic computing
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crystallographic teaching
crystallography in art and cultural heritage
crystallography of materials
electron crystallography
high pressure
inorganic and mineral structures
international tables
journals
magnetic structures
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congress

2020 iucr xxv
2017 iucr xxiv
2014 iucr xxiii
2011 iucr xxii
2008 iucr xxi
2005 iucr xx
2002 iucr xix
1999 iucr xviii
1996 iucr xvii
1993 iucr xvi
1990 iucr xv
1987 iucr xiv
1984 iucr xiii
1981 iucr xii
1978 iucr xi
1975 iucr x
1972 iucr ix
1969 iucr viii
1966 iucr vii
1963 iucr vi
1960 iucr v
1957 iucr iv
1954 iucr iii
1951 iucr ii
1948 iucr i

people

nobel prize

all
agre
anfinsen
barkla
boyer
w.h.bragg
w.l.bragg
brockhouse
de broglie
charpak
crick
curl
davisson
debye
deisenhofer
geim
de gennes
hauptman
hodgkin
huber
karle
karplus
kendrew
klug
kobilka
kornberg
kroto
laue
lefkowitz
levitt
lipscomb
mackinnon
michel
novoselov
pauling
perutz
ramakrishnan
roentgen
shechtman
shull
skou
smalley
steitz
sumner
thomson
walker
warshel
watson
wilkins
yonath

resources

commissions

aperiodic crystals
biological macromolecules
quantum crystallography
crystal growth and characterization of materials
crystallographic computing
crystallographic nomenclature
crystallographic teaching
crystallography in art and cultural heritage
crystallography of materials
electron crystallography
high pressure
inorganic and mineral structures
international tables
journals
magnetic structures
mathematical and theoretical crystallography
neutron scattering
NMR crystallography
powder diffraction
small-angle scattering
structural chemistry
synchrotron radiation
xafs

outreach

openlabs

calendar
OpenLab Costa Rica
IUCr-IUPAP-ICTP OpenLab Senegal
Bruker OpenLab Cameroon
Rigaku OpenLab Bolivia
Bruker OpenLab Albania
Bruker OpenLab Uruguay 2
Rigaku OpenLab Cambodia 2
Bruker OpenLab Vietnam 2
Bruker OpenLab Senegal
PANalytical OpenLab Mexico 2
CCDC OpenLab Kenya
Bruker OpenLab Tunisia
Bruker OpenLab Algeria
PANalytical OpenLab Turkey
Bruker OpenLab Vietnam
Agilent OpenLab Hong Kong
PANalytical OpenLab Mexico
Rigaku OpenLab Colombia
grenoble-darmstadt
Agilent OpenLab Turkey
Bruker OpenLab Indonesia
Bruker OpenLab Uruguay
Rigaku OpenLab Cambodia
PANalytical OpenLab Ghana
Bruker OpenLab Morocco
Agilent OpenLab Argentina
Bruker OpenLab Pakistan

- Letter from the President
- Guest editorial
- Diffractometer request
- Date error
- Well done
- Trichloroacetic acid
- Phase problem
- Charge density
- Amphiphilic lipid
- Molecular replacement
- Biphenyl
- Michelson
- Undulators
- Congress
- XD program
- Small molecules workshop
- Biomaterials
- ICDD
- PDC
- Structure factor file check
- CCDC update
- ECA prize
- ASRP Research Fellowships
- 50 years of DNA
- A. T. H. Lenstra (1942-2002)
- Edward C. Lingafelter (1914-2003)
- Henri A. Levy (1913-2003)
- Mary E. Mrose (1912-2003)
- Polymorphism in Molecular Crystals
- Enjoy Your Cells
- XX Congress and General Assembly update

Initial *E* map of the cyclosporin structure solved by *Neutron Shake-and-Bake*. The initial r.m.s. phase error is 37°. The hydrogen sites are displayed in negative (red) density while the C, N, O skeleton is displayed in positive (blue) density.

The crystallographic phase problem is formulated as a problem in constrained global minimization. In contrast to traditional direct-methods techniques using X-ray diffraction, this formulation does not require that the density function be positive everywhere. Instead, suitable generalization of the well known *Shake-and-Bake* formalism, here called *Neutron Shake-and-Bake*, exploits prior knowledge that the density function, as called for in the neutron diffraction case, is now permitted to assume negative, as well as positive, values. The initial application is made to the solution by *Neutron Shake-and-Bake* of the 199 atom (113 hydrogen atoms plus 86 nonhydrogen atoms) cyclosporin structure using experimental neutron diffraction data alone. Comparing the relative ease of this structure determination with the far greater challenge posed by the deuterated cyclosporin isomorph, in which the density function is positive everywhere, shows that, in sharp contrast to the prevailing view, the positivity of the density function not only does not facilitate, but actually substantially hinders, the phase determination process.

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