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• http://aflowlib.org/: AFLOW provides autonomous density functional theory and materials properties calculations.
• https://icsd.fiz-karlsruhe.de/​: ICSD-the world's largest database for completely identified inorganic crystal structures.
• https://it.iucr.org/: International tables for crystallography.
• https://materialsproject.org/​: Open-access database with prediction of materials electronic structures and properties.
• http://pd.chem.ucl.ac.uk/pdnn/symm3/allsgp.htm​: List of 230 3-dimensional space groups.
• https://www.cryst.ehu.es/​: Bilbao crystallographic server.
• http://www.op.titech.ac.jp/lab/mori/EHTB/EHTB.html: Atomic parameters for extended Huckel calculation.
• https://journals.iucr.org/services/cif/reqditems.html: List of items that are required for a single-crystal study.
• https://stokes.byu.edu/iso/findsym.php: FINDSYM-help to identify space group of a crystal with atomic positions.
• https://www.ncnr.nist.gov/resources/n-lengths/: Neutron scattering lengths and cross sections.
• https://wiki-ext.aps.anl.gov/ug11bm/index.php?title=GSAS_Profile_Terms: GSAS Profile Terms.
• https://matdata-asminternational-org.pitt.idm.oclc.org/apd/index.aspx: ASM alloy phase diagram database.
• https://mediaspace.unm.edu/media/Practical+Introduction+to+X-ray+Crystallography/1_if646wrm: An introduction lecture for XRD.
• More are coming......