John R. Rodgers

CRYSTMET: a database of the structures and powder patterns of metals and intermetallics

CRYSTMET is a database of critically evaluated crystallographic data for metals (including alloys, intermetallics and minerals) and associated bibliographic, chemical and physical information. Also included are simulated powder diffraction patterns for all of the entries. The database currently contains almost 70,000 entries and covers the literature exhaustively from 1922 to the present. The database is available on CD-ROM with search/analysis software for use on personal computers. This software can be used with any database in the appropriate format; currently CRYSTMET and the ICSD databases are available. This paper describes the database content, the procedures used in its construction, the software made available to the user and a number of potential uses for the data.

Quantum software interfaced with crystal-structure databases: tools, results and perspectives

Version 2.0 of Toths Materials Toolkit runs under Windows and prepares ASCII input files for popular ab initio packages such as ABINIT, VASP etc. Those packages, obtainable from their respective developers, may run in desktop or supercomputer setups with Linux or Windows operating systems. The Toolkit input is taken at will from a direct plug into CRYSTMET, with 93000 crystal-structure entries for metals and inorganic compounds, from CIF files of public-domain crystal-structure databases, or cut-and-paste from electronic journals followed by minimal free-format editing. The collection of fully general and highly graphical tools grouped on two command screens operates on the structure description stored in an editable ASCII screen. After the model has been searched, modified and evaluated in a few keystrokes with the above tools, its ASCII input files for a selection of ab initio packages are produced by selecting the meaningful flags and run options on a dialog. The tedious structure manipulation or decomposition into multiple simulations is performed in the background. Execution is followed by production of a plain-English job report. Four examples among the numerous possible applications of the Toolkit illustrate the fact that daunting topics, like the symmetry of chlorapatite, the voids and channels in the hydrogen-storage material EuNi5, the energy per unit area of the contact plane for spinel twin in diamond, and the hardness of lonsdaleite versus diamond, are amenable to processing by materials scientists more versed in experiment than theory. The manual with tutorials and availability information can be found at http://www.tothcanada.com/toolkit/.

Ab initio Stiffness for Low Quartz and Calcite

Ab-initio stiffness values were computed in an automated way for two trigonal reference materials: dextro low quartz and calcite with respective space groups P3 2 21 and R3c. Both were computed in their IRE settings, namely with r faces indexed [1011] for right-quartz and with obverse setting of the rhombohedral lattice in the hexagonal axes for calcite. The VASP total energy and stress engine was used for the calculations. Results in the order C 11 , C 12 , C 13 , C 14 , C 33 , C 44 are 82, 2, 10, -20, 98, 63 GPa for quartz and 159, 70, 63, +20, 98, 39 GPa for calcite. Quartz results are in good agreement with printed literature values. Comparison with experimental values for calcite disclosed a reverse orientation of the rhombohedral lattice in the hexagonal axes for the measurements that had not been clearly reported but was still recoverable from one sufficiently detailed reference. In spite of its current limited accuracy on extracted elastic coefficients, ab-initio calculation of elastic coefficients may already be a reliable way to complement and assist the experiment in its most difficult aspects.

Symmetry-general ab initio computation of physical properties using quantum software integrated with crystal structure databases: results and perspectives

The timely integration of crystal structure databases, such as CRYSTMET, ICSD etc., with quantum software, like VASP, OresteS, ElectrA etc., allows ab initio cell and structure optimization on existing pure-phase compounds to be performed seamlessly with just a few mouse clicks. Application to the optimization of rough structure models, and possibly new atomic arrangements, is detailed. The ability to reproduce observed cell data can lead to an assessment of the intrinsic plausibility of a structure model, even without a competing model. The accuracy of optimized atom positions is analogous to that from routine powder studies. Recently, the ab initio symmetry-general least-squares extraction of the coefficients of the elastic tensor for pure-phase materials using data from corresponding entries in crystal structure databases was automated. A selection of highly encouraging results is presented, stressing the complementarity of simulation and experiment. Additional physical properties also appear to be computable using existing quantum software under the guidance of an automation scheme designed following the above automation for the elastic tensor. This possibility creates the exciting perspective of mining crystal structure databases for new materials with combinations of physical properties that were never measured before. Crystal structure databases can accordingly be expected to become the cornerstone of materials science research within a very few years, adding immense practical value to the archived structure data.

Modeling of hP3 intermetallics in space group P-3m1: Calculated powder patterns from CRYSTMET ® X-ray cell data and ab initio coordinates

There are 39 CRYSTMET ® entries in the hexagonal space group P-3m1 (164) reporting both distinct pure phase compounds and atomic coordinates. Having the same Wyckoff positions in the same space group as the C6 structure type, all are isopointal with it. The range of observed c/a values extends from about 0.65 to 1.83. Three types are distinguished: Layered materials with CdI 2 type, the CeCd 2 type which is a slight distortion of the hexagonal AlB 2 type, and the intermediate EuGe 2 type made of the materials AuTe 2 , BaSi 2 , EuGe 2 , and SrGe 2 . Ab initio modeling of the 26 entries with CdI 2 and EuGe 2 type and atomic coordinates reproduces convincingly both their c/a axial ratios and z coordinates. For CoO 2 and SiTe 2 , both c/a and z deviate to a degree from the reported values, indicating that those materials should be reexamined for superstructures, stoichiometry, etc. Ab initio modeling of the 11 cell-and-type entries with CdI 2 type and no coordinates in CRYSTMET reproduced convincingly their reported axial ratios. The X-ray cell data and the ab initio z coordinates were then used in the production of reliable calculated powder patterns for CoTe 2 , CrSe 2 , HfS 2 , HfSe 2 , HfTe 2 , NbTe 2 , SnSe 2 , VS 2 , VTe 2 , ZrS 2 , and ZrTe 2 . All 11 patterns have been inserted in the intense diffraction line search system of CRYSTMET operated under the Materials Toolkit. Comparison of calculated patterns for SnSe 2 and ZrTe 2 with experimental entries in the PDF exposes the complementarity of calculated and experimental powder patterns and suggests that JCPDS pattern #15-223 should be reinterpreted in terms of the CdI 2 structure type. The CeCd 2 ⇔AlB 2 type transformation is modeled and discussed on YCd 2 using both ab initio methods and a hard-sphere model. For z ab initio solution is identical with that from the hard-sphere model while a quantum regime is predicted in the small region 0.45 z 2 abruptly transforms to the AlB 2 type. In spite of the new understanding gained, this modeling fell slightly short of allowing calculation of z values and powder patterns for the materials CaHg 2 , DyHg 2 , ErCd 2 , GdHg 2 , HoCd 2 , HoHg 2 , LuCd 2 , NdCd 2 , SmHg 2 , TbCd 2 , and TbHg 2 with no coordinates in CRYSTMET.