All qualified Texas A & M University employees and visiting scholars may use the facilities provided they have completed the required X-ray safety and instrument training and have the approval of the Department of Chemistry and their supervisor.
All Industrial Users goto the All Users link (to the left) for more information.
To get started you should know what you require from X-ray Diffraction (powder or single crystal) and what you have (a crystal, powder, solid etc.) to analyze.
To answer some of these questions start with the FAQ section below.
You may want to use X-ray Diffraction if
You want a molecular or extended structure and you have a large (> 100 micron) single crystal
You have a crystalline powder and you want to determine its powder pattern. About 1gram of Powder ground to about 50-100microns.
You have a solid that is semi-crystalline and you want to characterize it. Material should be no more than 1cm on each side and 1cm deep with a flat surface.
Complete online training here
Complete all Necessary Forms
Have your advisor sign the Key Request Form and the Building Security Form and bring all four forms to room 2408 for the signature of the X-ray Diffraction Laboratory Manager
Register and aggree to the policies and procedures of the X-ray Diffraction Laboratory
For more information go to the All Users section of the website
FAQ..
What
is X-ray Diffraction?
Why do you
use X-rays?
Why do
you use crystals?
How do
you determine molecular structure from X-rays and Crystals?
What
are crystal lattices and the unit cell?
What
are the Bravais Lattices?
What is a Space Group?
Local
Question (for Laboratory users)
How and
where to submit samples
To
reserve instrument time you must...
How much will
it cost?
Do I you
need general X-ray safety training YES IF ..
What free
crystallographic programs do I need to get started ...
If the X-ray
lab collects my data and I want to solve and refine my structure ...
How do I
access the Cambridge Data Base?
I need help on solving and/or refining my structure
General
Questions
How
do I grow good crystals?
How
do I mount my sample?
Odds and Ends
Historical
Must
Read Book List for Crystallographers
Basic Information
X-rays scatter off of electrons, in a process of absorption and re-admission. Diffraction is the accumulative result of the x-ray scattering of a group of electrons. For an incident X-ray photon of monochromatic wavelength ?, coherent waves are produced at an angle of theta (2-theta with respect to the incident x-ray) if the electron groups interact with the x-ray and are spaced at a distance d. The interaction is described by Bragg's law : nlamda =2dsin(theta). The intensity of the scattered x-ray is proportional to the number of electrons that the x-ray is scattered from.
Normally one would use a microscope to view small objects. For a microscope, light is scattered by an object and collected using lenses, which in turn magnifies the image of the object. The limit of the microscope is intrinsic to the nature of the electromagnetic radiation that is used to probe the object. If we use light we cannot look at objects smaller than the wavelength of light which is about 10 -6 m. Since the atom has dimensions of about 10-10 m we cannot image an atom with a photon of light. X-rays, on the other hand, have a wavelength of about 10 -10 m and are suitable for imaging objects at the atomic scale.
To observe a single object, we normally fix the object to a microscope slide. To view an atom we would need some method to handle a small atom and align it in the microscope. This would be quite difficult and the x-rays scattered by a single atom is extremely week. A better method is to use 1020atoms (the number found in a small -crystal) and to sum the scattered x-rays from each atom. The trick is to align the atoms in neat orderly rows and columns so that the scattered x-rays would form predictable patterns that are based on the original arrangement of the atoms. All of the atoms of a single-crystal are oriented the same way and the scattered x-rays are superimposed and can be measured. Each scattering event that is measures is called a "reflection". There is typically 2000 to 100000 independent reflections for each single-crystal.
We can determine Molecular Structure ....
The scattered x-rays contain both angular and intensity information. The information concerning the position of the electrons (and atoms) involves both the amplitude and phase of the scattered intensities. For standard data collection techniques the amplitudes for the diffracted intensities are measured, however the phases are lost due to the nature of the experiment. Direct methods is employed to re-determine the phases.
Structure determination is the process of model building, structural factor (intensity) prediction and comparison to the observed structure factors. The model is constructed by introduction of atomic positions at electron density maxima. The model is then employed to predict structural factors which are refined (non-linear least squares) against the observed structural factors. The comparison between the predicted and observed structure factors is known as the residual and attests for the validity of the model.
Crystal Lattice and the unit cell are ...
A single-crystal is described as an order set of atoms (electrons) in a fixed orientation. Typically a single crystal suitable of analysis is at least 50 µm in its smallest dimension and not more than 500 µm in its largest. The smallest non-reproducible volume of the crystal is called the unit cell. The size of the unit cell ranges from a few hundred cubic angstroms (10-10 m) to 10's of thousands. By application of symmetry the unit cell can be repeated, in three dimensions, to describe the entire crystal. The unit cell in turn can be described by three non-coplanar axis a, b and c and the inter axis angles alpha ,beta and gamma which are called the Lattice Parameters. Seven crystal systems are described in terms of the lattice parameters
| SYSTEM | UNIT CELL LENGTH | UNIT CELL ANGLES |
| 1) Cubic | a = b = c | alpha=beta=gamma=90deg |
| 2) Tetragonal | a = b | alpha=beta=gamma=90deg |
| 3) Orthorhombic | no conditions | alpha=beta=gamma=90deg |
| 4) Rhombohedral | a = b = c | alpha=beta=gamma does not equal 90deg |
| 5) Hexagonal | a = b | alpha=beta=90deg gamma=120deg |
| 6) Monoclinic | no conditions | alpha=beta=90 deg |
| 7) Triclinic | no conditions | no conditions |
| Lattice | Symbol |
| 1) Primitive | P |
| 2) (single face centered cells) | |
| A face (bc plane) - centered | A |
| B face (ac plane) - centered | B |
| C face (ab plane) - centered | C |
| 3) Face - centered | F |
| 4) Body - centered | I |
Space groups are a way of describing how objects are arranged in three-dimensional space. There are four symmetry operations allowed in three dimensional "space".
| Operation | Symbol (Hermann) | Symbol (Schoenflies) |
| Rotation | 1,2,3,4,6 | E, C2, C3, C4, C6 |
| Reflection | m | Cm |
| Inversion | -1, 2/m | i |
| Rotation/Inversion | -1,-3,-4,-6 | n/a |
A symmetry operation followed by translation is also allowed
Screw axis 21, 31, 32, 41, 43, 61, 65
Glide planes a,b,c,n,d
A space group is described as a closed set of symmetry operations that describe the total symmetry of a given volume of space (unit cell). The first letter of the space group describes the centered cell (P, A, B, C, F or I). The following symbols represent the smallest set of non-reducible symmetry operations.
e.g. Pmmm Primitive cell with three perpendicular mirror planes
Local Questions
How and where to submit samples
Submit your samples to the X-ray staff for approval. Bring your sample to rm 2409 between 9:00am-5:00pm weekdays
There are two ways to submit your sample and determine your structure.
1st ) You can request that
the x-ray diffraction laboratory staff undertake the investigation.
This way
is suggested if ...
a) you
undertake only a few structural determinations a year
b) your
advisor does not want you to undertake the time and expense of
learning a new skill.
2nd ) You can be trained and
you can do your own work. This method is suggested if ...
a) your
structures are major part of your research
b) you
must defend your structures before skeptical investigators
To reserve instrument time ...
To reserve time please use the
calendar reservation system.
Call 979-845-9125 for information
Yes you need safety training IF ...
Yes !! : If you intend to do your own structures
No : If you wish for the staff to do your structures
X-ray Safety Training
Before you begin the x-ray staff will train you on the site specific safety issues.
Goto NEW USERS page for further details.
Free crystallographic programs to get started ....
You should download some of the free crystallographic software on the net
a)WinGX - A GUI (windows) for some of the most popular (and free) software. First download the software and then e-mail the author for a free license. SHELXS, SHELXL, PLATON, SIR92 and several other valuable programs come with the package.
b)GTREP - A structure graphics and plotting program. Will plot thermal ellipsoids.
C)Mercury from the CSD
If the X-ray lab collects the data we will provide ..
You will be given (at least) two files project_name.HKL and project_name.INS The X-ray Staff will assist you the first few times.
The Cambridge Crystallographic Data Base can be ..
The Cambridge
Crystallographic Data Base is located on a PC computer in the X-ray Facility
or through WebCSD (tamu
domain only)
General Questions
Crystals : See Growing Crystals
Recommended reading
P.G. Jones:
Crystal growing, Chemistry in Britain (1981) 17, 222-225.
J. Hulliger:
Chemistry and Crystal Growth, Angew. Chem. Int. Ed. Engl. (1994) 33,
143-162. Angew. Chem. (1994) 106, 151-171.
A. Holden, P.
Morrison: Crystals and Crystal Growing, MIT Press, Cambridge,
Massachusetts (1982) ISBN 0-262-58050-0
J.W. Mullin:
Crystallization, Butterworth-Heinemann, Oxford, Great Britain (1993)
ISBN 0-7506-1129-4
How do
I mount my sample?
Two methods are commonly employed.
a)Thin
glass fiber
A thin glass fiber is pulled
and attached to a copper pin (magnetic base, Hampton) with clay and
finger nail polish. The fiber can be pulled by heating a
Klimax® melting point tube in a hot flame. The fiber is
typically 50 to 100 mm in diameter. The crystal is glued to the
fiber with an adhesive.
b)Nylon loop or
Mylar loop
A thin (thickness =
20mm) 0.7 mm diameter nylon loop (Hampton) that is attached to
a magnetic base is coated with Paratone® or Apieazon®
grease is used to "lasso" (Texas style) a crystal and
pulled it off the microscope plate.
Hints
-Crystals can be covered with
a thin layer of oil to prevent decomposition in air.
Mineral oil.
Paratone® (a
poly-isobutylene: additive free STP)
Poly-isobutylene (is
available in several viscosities)
Perfluorinated oils
(Krytox® oil)
Epoxy resin (less hardener)
Apieazon® grease
-If your crystals lose
solvent, try adding a few drops of the solvent (mother liquor) to
mineral oil or paratone and then cover the crystals with this
mixture. Some experimentation on solvent concentrations in the
oil may be needed.
-Adhesives for specimen pins
super
glue
holds up to 373K dries fast
dental
cemen
to 573K dheres to glass well
Epoxy
resins
to 373K slow drying
Apiezon®
Grease(T)
to 103K low scatter
Silicon Grease (not
4)
to 133K Si scatter (cheap)
Vaseline
to 200K
sticky
Balsam
to RT dilute with
xylene
Wax
to RT
permanent
Crystallographic Papers
Birth of Crystallography :
1669 Nicolaus Skno : Determined that angles between crystal faces remained constant between crystals of the same compound.
1895 Rontgen :
Discovers X-rays : Science (1896) 53, 274. (in English)
First X-ray Diffraction
Experiment : Friedrick, W. Knipping, P. & Laue,
M. Bravarian Acad. Sci. (1912) 303.
First Structure Determination
: Bragg, W.H & Bragg W.L. Proc. Royal. Soc. (1913) A88, 428.
First X-ray Camera (Powder):
Debye, P. & Scherrer, P. Phys Z. (1916) 17, 277-283.
Hull, A. W. Phys. Rev. (1917) 10, 661-696.
First X-ray Diffraction
Instrument: Weissenberg, K. Z.Phys. (1924) 23, 229.
First Geiger Counter:
Locher, G.L. & LeGalley, D.P. Phys. Rev. (1933) 46, 1047.
First X-ray Precession
Instrument : Buerger, M.J. "X-ray Crystallography"
(1942) Wiley, New York
First Scintillation Counter:
West, H.I., Mayerhot, W.E., Hotstadter, R. Phys. Rev. (1951) 81, 141.
Top Ten Must Read Crystallographic Books.
1. Crystal structure determination by: Werner
Massa
"My favorite introduction to Crystallography"
"It's the one book I would force into a
student hands!"
2. Crystal Structure Analysis by: Glusker and Trueblood
"A good starter for the common scientist"
3. Crystal Structure Determination and Crystal Structure
Analysis by: Bill Clegg
"One of my favourite and informative
book(s). First time crystallographers should read these books first."
4. Cystallography Made Crystal Clear by: Gale Rhodes
"For the Novice/macromolecular user"
5. Fundamentals of Powder Diffraction and Structural
Characterization of Materials by: Pecharsky and Zavalij
"Only book that I know of that explains
indexing and indexing programs"
"A must own book for the powder and
single-crystal diffractionist!"
"A gota-have book for people interested in
the bigger picture"
6. Structure Determination by X-ray Crystallography by: Ladd and Palmer
"I have given Ladd
and Palmer to non-crystallographers who needed to gain
a basic
understanding of the process."
7. X-ray Structure Determination by: Stout and Jensen
"a good, practical book for
the student after they are into the subject"
8. X-ray Analysis and the Structure of Organic Molecules by: Dunitz
"a
great book (even for an inorganic chemist) and it is filled Jack's
usual wit"
"The
section on weighting schemes in least squares is a must read"
9. The Determination of Crystals Structures by: Lipson & Cochran
"It
is still an amazing book!"
10. Fundamentals of Crystallography edited by C. Giacovazzo
"A MUST HAVE for a lab"
"For
more advanced students Giacovazzo is a must."
Tests for Center of Symmetry
Wilson, A.J.C. (1949) Acta
Cryst., 2, 318-321.
Howells, E.R.; Phillips, D.C.
& Rogers D. (1950) Acta Cryst., 3, 210-214.
Marsh, R.E. (1986) Acta
Cryst., B42, 193-198.
Crystallographic Information File
CIF format :: I.U.Cr.
Commission on Crystallographic Data:
S.R. Hall, F.H. Allen and
I.D. Brown (1991) Acta Cryst., A47, 655-685.
Chemical
Group Modeling
Ipso-angles of phenyl
rings differ systematically from 120 degrees
P.G. Jones (1988) J.
Organomet. Chem., 345, 405
T. Maetzke and D. Seebach
(1989) Helv. Chim. Acta, 72, 624-630
A. Domenicano, "Accurate
Molecular Structures", eds. Domenicano and Hargittai, Chapter
18, OUP (1992)
Standard (restraint) bond
lengths based on the CSD
F.H.Allen, O. Kennard, D.G.
Watson, L. Brammer, A.G. Orpen and R. Taylor in Sections 9.5 and 9.6
of Volume C of "International Tables for Crystallography"
(1992), Ed. A.J.C. Wilson, Kluwer Academic Publishers, Dordrecht, pp.
685- 791.
Standard (retraint) bond
lengths for protiens
R.A. Engh and R. Huber (1991)
Acta Cryst., A47, 392-400.
Standard (restraint) bond
lengths For nucleic acids
R. Taylor and O. Kennard
(1982) J. Mol. Struct., 78, 1-28 (bases and phosphates)
S. Arnott and D.W.L. Hukins
(1972) Biochem. J., 130, 453-465 (furanose rings).
Plainarity of nucleic acid bases
R. Taylor and O. Kennard
(1982) J. Am. Chem. Soc., 104, 3209-3212
Diffuse solvent modeling
by Babinet's principle
R. Langridge, D.A. Marvin,
W.E. Seeds, H.R. Wilson, C.W. Hooper, M.H.F. Wilkins and L.D.
Hamilton (1960) J. Mol. Biol., 2, 38-64
H. Driessen, M.I.J. Haneef,
G.W. Harris, B. Howlin, G. Khan and D.S. Moss, J. (1989) J. Appl.
Cryst., 22, 510-516
Rigid body analysis
Schomaker, V. and Trueblood,
K.N. (1968) Acta Cryst., B24, 63-76.
Data Collection and Reduction
Area Detection -CCD
strategies
S. Ruhl and M. Bolte (2000)
215, 499-509
Area Detection -peak bases
Bolotovsky, R.; White, M.A.;
Darovsky, A. and Coppens, P. (1995), J. Appl. Cryst. 28, 86-95.
Diffractometer
Alexander, L & Gordon
S.S. (1962) Acta Cryst., 15, 983-1004.
Diffractometer Alignment
Samson, S. and Schuelke, W.W.
(1967) Rev. Sci. Instr., 38, 1273-1283.
Cell reduction and Lattice Symmetry
Glegg, W. (1981) Acta Cryst.,
A37, 913-915.
Gruber, B. (1973) Acta
Cryst., A29, 433-440.
Scan type Wyckoff
Wyckoff, H.W.; Doscher, M.;
Tsernoglou, D.; Inagami, T.; Johnson, L.; Hardman, K.D.; Allewell,
N.M.; Kelly,M. & Richards, F. (1967) J. Mol. Biol., 27, 563-578.
Data Reduction
Blessing, R.H. (1987) Cryst.
Rev., 1, 3-58.
Blessing, R.H. & Langs,
D.A. (1987) J.Appl. Cryst., 20, 427-428.
X-ray beam and Detection
Harkema, S.; Dam, J.; Van
Hummel, G.J. and Reuvers, A.J. (1980) Acta Cryst., A36, 433-435.
Katrusiak, A. & Ryan,
T.W. (1988) Acta Cryst., A44, 623-627.
Nelson, J.T. & Ellickson,
R.T. (1955) J. Am. Opt. Soc., 45, 984-986.
Intensities
Slaughter, M. (1968)
Kristallogr., 129, 24-35.
McCanlish, L.E.; Stour. G.H.
and Andrews, L.C. (1975) Acta Cryst., A31, 245-249.
French, S. & Wilson, K.
(1978) Acta Cryst., A34, 517-525.
Learnt Profile Analysis
Diamond, R. (1969) Acta
Cryst., A25, 43-55.
Clegg, W. (1981) Acta Cryst.,
A37, 22-28.
Lehmann/Larsen method
Lehmann, M.S. & Larsen,
F.K. (1974) Acta Cryst., A30, 580-584.
Floating Baseline
Reibenspies, J.H. (1994)
J.Appl.Cryst. 26,426-430.
Normal Back/Peak/Back
Tickle, I.J. (1975) Acta
Cryst. B31, 329-331.
Slope Detection method
Grant, D.F. & Gabe, E.J.
(1978) J.Appl. Cryst. 11, 114-120.
Misc. procedures and investigations
Spencer S.A. and Kossiakoff
(1980) J. Appl. Cryst., 13, 563-571.
Dudka, A.P. and Loshmanov,
A.A. (1992) Sov. Phys. Crystallogr., 36, 625-626.
Langford, J.L. (1978) J.
Appl. Cryst., 11, 10-14.
Lehmann, M.S. (1975) J. Appl.
Cryst., 8, 619-622.
Chulichkov, A.I.;
Chulichkova, M.; Fetisov, G.; Pyt'ev,Y.P.; Lupyan, Y.V.;Laltionov,
A.V.; Nesterenko, A.P. and Aslanov, L.A. (1987) Sov. Phys.
Crystallogr., 32, 649-653.
van der Wal, H.R.; de Boer,
J.L. and Vos, A. (1979) Acta Cryst., A35, 685-688.
Strel'tsov, V.A. and
Zavodnik, V.E. (1989) Sov. Phys. Crystallogr., 34, 824-828.
Norrestam, R. (1972) Acta
Chem. Scand., 26, 13-21.
Rigoult, P. J. (1979)
J.Appl.Cryst., 12, 116-118.
Blessing, R.H.; Coppens, P.
& Beker, P. (1972) J. Appl. Cryst., 7, 488-492.
Rossman, M.G. (1979) J. Appl.
Cryst., 12, 255-238.
Reflection Intensity Photography
Xuong, N. & Freer S. Acta
Cryst., B27, 2380-2387.
Laue Film Integration &
Deconvolution
Shrive, A.K.; Clifton,I.J.;
Hajdu, J. and Greenhough T.J. (1990) J. Appl. Cryst., 23, 169-174.
Decay Correction
Abrahams, S.C. and Marsh, P.
(1987) Acta Cryst., A43, 265-269.
Ibers, J.A. (1969) Acta
Cryst., B25, 1667-1668.
Back
to Top
Extinction Correction
A.C. Larson in
"Crystallographic Computing" (1970), Ed. F.R. Ahmed,
Munksgaard, Copenhagen, pp. 291-294.
Larson, A.C. (1967) Acta
Cryst., 23, 664-665.
Zachariasen, W.H. (1963) Acta
Cryst., 16, 1139-1144.
Least Squares Refinement
Floating origin restraints:
H.D. Flack and D.
Schwarzenbach (1988) Acta Cryst., A44 499-506.
Use of all data in refinement.
F. L. Hirshfeld and D.
Rabinovich (1973) Acta Cryst., A29, 510-513
L. Arnberg, S. Hovmoller and
S. Westman (1979) Acta Cryst., A35, 497-499
Refinement of racemic twins
Pratt, Coyle and Ibers (1971)
J. Chem. Soc., 2146-2151
Jameson (1982) Acta Cryst.,
A38, 817-820.
Conjugated Gradient L. S. algorithm
W.A. Hendrickson and J.H.
Konnert "Computing in Crystallography", Ed. R. Diamond, S.
Ramaseshan and K. Venkatesan, I.U.Cr. and Indian Academy of Sciences,
Bangalore 1980, pp. 13.01-13.25.
D.E. Tronrud (1992) Acta
Cryst., A48, 912-916.
Least-Squares Restraints :
J.S. Rollett in
"Crystallographic Computing", Ed. F.R. Ahmed, S.R. Hall and
C.P. Huber, Munksgaard, Copenhagen, (1970) pp. 167-181.
F.L. Hirshfeld (1976) Acta
Cryst., A32, 239-244
K.N. Trueblood and J.D.
Dunitz (1983) Acta Cryst., B39,120-133.
.J. Didisheim and D.
Schwarzenbach (1987) Acta Cryst., A43, 226-232
Shift limiting
least-squares restraints (damping) Marquardt algorithm ::
Marquardt (1963) J. Soc. Ind.
Appl. Math., 11, 431-441.
Back
to Top
Program References
SHELXTL-PLUS
Sheldrick, G. (1990) SHELXTL-PLUS revision 4.11V, SHELXTL-PLUS users manual,Siemens Analytical X-ray Inst. Inc., Madison WI, U.S.A.
SHELXS-86
Sheldrick, G. (1986)
SHELXS-86 Program for Crystal Structure Solution, Institüt
für Anorganische Chemie der Universität, Tammanstrasse 4,
D-3400 Gottingen, Germany.
SHELXL-97
Sheldrick, G. (1997)
SHELXL-97 Program for Crystal Structure Refinement, Institüt
für Anorganische Chemie der Universität, Tammanstrasse 4,
D-3400 Gottingen, Germany.
TEXSAN
teXsan : Single Crystal
Structure Analysis Software, Version 1.6 (1993). Molecular Structure
Corporation, The Woodlands, Texas 77381.
DIRDIF-99
Beurskens, P., Admiraal, G.,
Beurskens G., Bosman, S., Garicia-Granda, R., Gould, J., Smykalla, A.
and Smykalla, C. (1992). DIRDIF-99 program system, Technical Report
of the Crystallography Laboratory, University of Nijmegen, The Netherlands
SIR-97
Giacovazzo C. (1997) SIR-97
Program for Crystal Structure Solution, Inst. di Ric. per lo Sviluppo
di Metodologie Cristallograpfiche, CNR, Univ. of Bari, Italy.
SIR-88
SIR88 : Burla, M.C.; Camalli,
M.; Ccascarano, G.; Giacovazzo, C.; Polidori, G. and Viterbo, D.
(1989) J. Appl. Cryst. 22, 389-393.
PATSEE
Egert, E. (1985) PATSEE
Program for Crystal Structure Solution by Integrated Patterson and
Direct Methods, Institüt für Anorganische Chemie der
Universität, Tammanstrasse 4, D-3400 Gottingen, Germany. Egert,
E. and Sheldrick, G. (1985) Acta Cryst A41, 262-268.
SHAKAL
SCHAKAL88 : Keller, E. (1989)
J. Appl. Cryst. 22, 12-22.
PLUTON
Spek, A.L.. (2002) PLUTON.
Program for Molecular and Crystal Graphics. Vakgroep Algemene Chemie,
University of Utrecht, Afdeling Kristal-En Structuurchemie, Padualaan
8, 3584 Ch Utrecht, The Netherlands.
PLATON
Spek, A.L.. (2002) PLATON.
Program for Crystal Structure Results Analysis. Vakgroep Algemene
Chemie, University of Utrecht, Afdeling Kristal-En Structuurchemie,
Padualaan 8, 3584 Ch Utrecht, The Netherlands.
ORTEP-76
Johnson, C.K. (1976)
ORTEP-II. A Fortran Thermal-Ellipsoid Program, Report ORNL-5138. Oak
Ridge National Laboratory, Oak Ridge Tennessee.
Back
to Top
Space
groups/ Laue symmetry / Unit cell
polar space groups
H.D. Flack and D.
Schwarzenbach (1988) Acta Cryst., A44 499-506
MISSYM
LePage, Y. (1987) J Appl.
Cryst., 20, 264-269
Lattice symmetry determination
Mighell, A.D. and Rodgers,
J.R. (1980) Acta Cryst., A36, 321-326.
Baur, W.H. and Tilmanns, E.
(1986) Acta Cryst., B42, 95-111.
Structure inversion for
special space groups
E. Parthe and L.M. Gelato
(1984) Acta Cryst., A40, 169-183
G. Bernardinelli and H.D.
Flack (1985) Acta Cryst., A41, 500-511
Statistical Descriptors in Crystallography
D. Schwarzenbach; Abrahams, S.C.; Flack, H.D.; Gonschorek, W.; Hahn, T;Huml, K.; Marsh, R.E.; Prince, E.; Robertson, B.E.; Rollet, J.S. and Wilson, A.J.C. (1989) Acta Cryst., A45, 63-75.
SHELXL-97
R. Herbst-Irmer, G. Sheldrick
(1998) Acta Cryst, B54, 443-449.
X-Ray Facilities
xray@tamu.edu
(979) 845-9123
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