>100.000 entries : >40.000 structures added to the ~60.000 entries of the PCOD version 2

These results were announced in the paper:
"Inorganic structure prediction with GRINSP."
A. Le Bail, J. Appl. Cryst. 38 (2005) 389-395.
(open access at the IUCr journals)
Three years of calculations were needed...

Note : Some two-dimensionnal models were not removed, many
of them are listed with the smallest framework densities (FD < 9 possibly)
(disconnected sheets, with one doubtful cell parameter).

Structure-types and isostructural compounds
Problem with electrical neutrality
Criticism of the method
Details of the series included into the PCOD

Problem with electrical neutrality :

Are electrically neutral : B₂O₃, SiO₂, V₂O₅, AlF₃ series, as well as combinations such as [SiO₄]/[BO₃], [SiO₄]/[VO₅], [BO₃]/[VO₅] (...) whatever their formulations (polyhedra - triangles, tetrahedra, octahedra, etc - which form neutral networks by exclusive corner sharing will also form neutral networks if combined - mixed tetrahedra/octahedra, etc - by exclusive corner sharing). Other series like [TiO₆]/[SiO₄] (...) would need for the occupation of holes by appropriate ions in order to attain the neutrality.

Quality improvements are expected to come from, in a first step, the application of bond valence rules in GRINSP. The list of 'to do' things for that software is quite long :
- provide the final models in the correct SG, not in P1 (for that, the O atoms placed at the midpoints between the cations have to be checked against the special and general positions of the SG selected at the beginning of the model building).
- the refinement part (working on the atomic coordinates and cell parameters) has obviously to take account of these special positions if any.
- the electrical neutrality of the network has to be checked and finally ensured -if possible- by an automatic system of detection of holes, these holes being filled in by appropriate ions.
- a new cost function based on bond valence rules should ensure better results than the simple cost function based on ideal interatomic distances, but this remains to be tested...

All this could well reduce the number of structure candidates in the PCOD from 100,000 to 10,000 or less, excluding 90% or more of possibly not-viable hypothetical models...  Wait and see...

Anyway, GRINSP can only produce structure candidates in the quite limited category of the N- and N-N'-connected 3D nets, nothing else... Is it possible to imagine an algorithm similar but allowing to extend the exploration domain to other polyhedra connections than corner sharing ? Maybe...

Shall we realize energy minimization (using GULP for instance) for each of the candidate structure to its local minimum and compare energies ? Systematic studies of zeolites and aluminophosphates [6-7] by this way have led to cell parameters agreement better than 1% in most cases, the worst disagreement is less than 2%. By the use of the simple cost function based on ideal interatomic distances with GRINSP, the agreement is already generally close to that (less than 2%), this being due to the 3D network nature of these models, among other reasons.

Another imperfection in GRINSP is related to the way the models are recognized to be identical or different. This is done through the coordination sequence (CS) which is known to be not completely sure (examples are known of a few different zeolites presenting the same CS up to the 10th shell or more, and being still structurally different). But even if a few structures were excluded wrongly by this imperfect system, there are probably worse things occuring which allow for the selection of structure candidates that should not be kept in the lists...

Rendez-vous in 2009 for a new GRINSP-3 version ? Who knows...

References

[1] Le Bail, A. (2005). “Inorganic structure prediction with GRINSP,” J. Appl. Crystallogr. 38, 389–395.
[2] Le Bail, A. (2007). “Predicted corner-sharing titanium silicates,” Z. Kristallogr. suppl. 26, 203–208.
[3] Le Bail, A. (2007). “Inorganic structure prediction: Too much and not enough,” Solid State Phenom. 130, 1–6.
[4] Le Bail, A. and Calvayrac, F. (2006). “Hypothetical AlF₃ crystal structures,” J. Solid State Chem. 179, 3159–3166.
[5] Le Bail, A. (2008). "Frontiers between crystal structure prediction and determination by powder diffractometry," Powder Diffraction, in the press.
[6] Henson, N.J., Cheetham, A.K. and Gale, J.D. (1994). Chem. Mater. 6, 1647.
[7] Henson, N.J., Cheetham, A.K. and Gale, J.D. (1996). Chem. Mater. 8, 664.

1- Triangles series

Formulation : B₂O₃
766 models with R < 0.006
Entries : PCOD1500001 to PCOD1500766
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
 
 

2- Tetrahedra series

Formulation : SiO₂
6022 models with R < 0.015
Entries : PCOD3100001 to PCOD3106022
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Formulation : known-SiO₂
129 models corresponding to known zeotypes
Entries : PCOD3000201 to PCOD3000329
List sorted by FD

Mixte tetrahedra AlO₄/SiO₄
6081 models with R < 0.015
Entries : PCOD4400001 to PCOD4406081
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : Al and Si are ordered

Mixte tetrahedra AlO₄/PO₄
6391 models with R < 0.015
Entries : PCOD3300001 to PCOD3306391
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : Al and P are ordered

Mixte tetrahedra AlO₄/SO₄
5600 models with R < 0.015
Entries : PCOD4500001 to PCOD4505600
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : Al and S are ordered
 
 
 

3- Square-based pyramids

Formulation : V₂O₅
1318 models with R < 0.015
Entries : PCOD5000001 to PCOD5001318
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Formulation : Mn₂O₅
1295 models with R < 0.015
Entries : PCOD5010001 to PCOD5011295
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the V₂O₅ series
 

4- Octahedra series

Formulation : AlF₃
33 models with R < 0.020
Entries : PCOD6000001 to PCOD6000033
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : these new entries are to be added to the previous ones described in  the paper
"Hypothetical AlF₃ crystal structures."
A. Le Bail & F. Calvayrac, J. Solid State Chem., 179 (2006) 3159-3166.

Formulation : FeF₃
33 models with R < 0.020
Entries : PCOD6001001 to PCOD6001033
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Formulation : GaF₃
33 models with R < 0.020
Entries : PCOD6002001 to PCOD6002033
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Formulation : CrF₃
32 models with R < 0.020
Entries : PCOD6003001 to PCOD6003032
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Mixte polyhedra AlF₆/CaF₆
24 models with R < 0.020
Entries : PCOD6010001 to PCOD6010024
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Mixte polyhedra AlF₆/NaF₆
13 models with R < 0.020
Entries : PCOD6011001 to PCOD6011013
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
 
 

5- Tetrahedra-triangles series

Mixte polyhedra : SiO₄/BO₃
3603 models with R < 0.010
Entries : PCOD7000001 to PCOD7003603
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF

Mixte polyhedra : PO₄/BO₃
3457 models with R < 0.010
Entries : PCOD7010001 to PCOD7013457
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
isostructral with the SiO₄/BO₃ series

Mixte polyhedra : SO₄/BO₃
3212 models with R < 0.010
Entries : PCOD7020001 to PCOD7023212
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
 
 

6- Square-based pyramid-triangles series

Mixte polyhedra : VO₅/BO₃
4873 models with R < 0.015
Entries : PCOD1530001 to PCOD1534873
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
 
 

7- Octahedra-triangles series

Mixte polyhedra : AlO₆/BO₃
4138 models with R < 0.012
Entries : PCOD6100001 to PCOD6104138
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
 
 
 
 

8- Octahedra-tetrahedra series

Mixte polyhedra : TiO₆/SiO₄
2154 models with R < 0.020
Entries : PCOD3201001 to PCOD3203154
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Notes : this is the complete list of titanosilicates (previous entries 3200000-etc).
Papers discussing these titanosilicates are :
Le Bail, A. (2007). “Predicted corner-sharing titanium silicates,” Z. Kristallogr. suppl. 26, 203–208.
    (supplementary material  - .doc file - for that publication above which was limited to 6 pages on the titanosilicates...)
Le Bail, A. (2007). “Inorganic structure prediction: Too much and not enough,” Solid State Phenom. 130, 1–6.
 
 

Mixte polyhedra : TiO₆/PO₄
1975 models with R < 0.020
Entries : PCOD3230001 to PCOD3231975
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : TiO₆/SO₄
1821 models with R < 0.020
Entries : PCOD3240001 to PCOD3241821
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : GaO₆/SiO₄
1953 models with R < 0.020
Entries : PCOD6490001 to PCOD6491953
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : GaO₆/PO₄
1913 models with R < 0.020
Entries : PCOD3210001 to PCOD3211913
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : GaO₆/SO₄
1779 models with R < 0.020
Entries : PCOD6480001 to PCOD6481779
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : NbO₆/SiO₄
2014 models with R < 0.020
Entries : PCOD3220001 to PCOD3222014
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : NbO₆/PO₄
1859 models with R < 0.020
Entries : PCOD6470001 to PCOD6471859
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : NbO₆/SO₄
1565 models with R < 0.020
Entries : PCOD6460001 to PCOD6461565
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : VO₆/SiO₄
2038 models with R < 0.020
Entries : PCOD6400001 to PCOD6402038
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : VO₆/PO₄
1938 models with R < 0.020
Entries : PCOD6420001 to PCOD6421938
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : VO₆/SO₄
1743 models with R < 0.020
Entries : PCOD6410001 to PCOD6411743
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : ZrO₆/SiO₄
1958 models with R < 0.020
Entries : PCOD6450001 to PCOD6451958
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : ZrO₆/PO₄
1754 models with R < 0.020
Entries : PCOD6430001 to PCOD6431754
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates

Mixte polyhedra : ZrO₆/SO₄
1469 models with R < 0.020
Entries : PCOD6440001 to PCOD6441469
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the titanosilicates
 
 
 
 

9- Octahedra-square-based pyramids series

Mixte polyhedra : TiO₆/VO₅
2045 models with R < 0.020
Entries : PCOD4300001 to PCOD4302045
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
In that series can be found some oxygen-deficient perovskites.

Mixte polyhedra : VO₆/VO₅
1997 models with R < 0.020
Entries : PCOD5600001 to PCOD5601997
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the TiO₆/VO₅ series above

Mixte polyhedra : GaO₆/VO₅
1963 models with R < 0.020
Entries : PCOD5620001 to PCOD5621963
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the TiO₆/VO₅ series above

Mixte polyhedra : NbO₆/VO₅
1928 models with R < 0.020
Entries : PCOD5610001 to PCOD5611928
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the TiO₆/VO₅ series above

Mixte polyhedra : ZrO₆/VO₅
1843 models with R < 0.020
Entries : PCOD5630001 to PCOD5631843
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the TiO₆/VO₅ series above

Mixte polyhedra : MnO₆/MnO₅
1507 models with R < 0.020
Entries : PCOD5640001 to PCOD5641507
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the TiO₆/VO₅ series above
 
 

10- Square-based pyramids - tetrahedra series

Mixte polyhedra : VO₅/PO₄
2394 models with R < 0.015
Entries : PCOD4000001 to PCOD4002394
Lists sorted by R, by FD
Multiple CIF
Connectivity sequences

Mixte polyhedra : VO₅/SiO₄
2424 models with R < 0.015
Entries : PCOD4010001 to PCOD4012424
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : VO₅/SO₄
2364 models with R < 0.015
Entries : PCOD4020001 to PCOD4022364
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : TiO₅/SiO₄
2541 models with R < 0.015
Entries : PCOD5400001 to PCOD5402541
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : TiO₅/PO₄
2446 models with R < 0.015
Entries : PCOD5410001 to PCOD5412446
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : TiO₅/SO₄
2083 models with R < 0.015
Entries : PCOD5420001 to PCOD5422083
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : MnO₅/PO₄
2449 models with R < 0.015
Entries : PCOD5430001 to PCOD5432449
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : MnO₅/SO₄
2067 models with R < 0.015
Entries : PCOD5440001 to PCOD5442067
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄

Mixte polyhedra : MnO₅/SiO₄
2541 models with R < 0.015
Entries : PCOD5450001 to PCOD5452541
Lists sorted by R, by FD
Connectivity sequences
Multiple CIF
Note : isotypical with the VO₅/PO₄