Crystallographer Scientist

Location

Gaithersburg, MD | United States

Job description

Title: Crystallographer Scientist

Location: Gaithersburg, MD

Status: Full-Time (On-Site)

Position Summary:

The National Institute of Standards and Technology (NIST), Standard Reference Database 84 (Inorganic Crystal Structure Database, ICSD) is a comprehensive collection of crystal structure data of inorganic compounds containing about 200,000 entries and covering the literature from 1913. Crystallographic data stored in the ICSD describes the infinite set of atomic configuration points that each crystalline material has in a 3-dimensional space. The ICSD database has been widely used for reconstruction of the crystal structures to do phase identification and scientific computations, such as X-ray/ electron/ neutron diffraction simulation, first principle calculation, etc.

Many of the scientific applications involve, to various degrees, the non-trivial task of structure comparison for identification, association, or cross checking of structural models. A hierarchy of nomenclature was proposed to define inorganic Structure Types to the different degrees of similarity between structures (isopointal, isoconfigurational, crystal-chemically isotypic, etc.) 1• Based on proposed criteria of isoconfigurational structures, the ICSD has been implementing a Structure Type classification to form subsets that have comparable crystallographic point configuration and geometrical relationships.

The process is done by selecting structures from the database that can form a set based on a series of criteria (space group numbers / symbols, Wyckoff, Pearson's symbols, ANX formula, c/a ratio, beta ranges, etc.), and assigning each set with a formula and a "prototype" representation2. These assignments have been done manually by experts in the field for each individual compound.

Structure Types provide database users one way to find compounds of interest in the database that are comparable to each other. However, these subsets are discrete, exclusive clusters, created arbitrarily with regard to their chemical/geometrical/physical interrelationships. The differentiation and possible connection of the Structure Types are not readily measurable. At the same time, because the transition between different structures could have no clear boundary, the choice of exclusive representations from a continuous range could miss the recognition of similarity around the boundary definitions.

Over the past decades, multiple lists of Structure Types, in databases or handbooks, have been created by experts doing critical evaluations on different kinds of data sets. In addition, there are domain-specific nomenclatures and systems of representative types used in publications within different research fields. These definitions fall short of providing a consistent systematic framework for implementation and were developed with more specific needs in certain structural, physical, chemical, and engineering properties. With the comprehensiveness of its inorganic crystal structure collection, NIST SRD84 ICSD provides a unique platform for a generalized systematic approach to model, compare and define Structure Types. The Structure Type enhancements proposed herein should prove to the benefit of all users.

Duties/Responsibilities:

1. The Contractor shall work through the current ICSD 9,000 Structure Type definitions, to examine, define, and categorize, to the extent possible, the identified (manually implemented) conventions, procedures, and description of atomic arrangements.
2. Based on the findings of Task I, the Contractor shall select approximately 1,500 Structure Types from the original set of-9,000 Structure Types currently used within ICSD. It is estimated that the selection of-1500 Structure Types will enable a secondary set of approximately 30,000 to 50,000 ICSD database entries to be created. The Contractor shall analyze the -30-50K set of database entries to compare individual entry's representative data and evaluate geometric/crystallographic relationships between entries. The Contractor shall analyze 3-D atomic coordinates between entries.
3. The Contractor shall design a preliminary set of rules to relate comparable structures in the selected subset of -30-50K database entries from Task 2. It is anticipated that some Structure Types may be related to a different Structure Type through different types of transformations (i.e. crystallographic and geometric mappings, and transformations). The Contractor shall use an iterative improvement strategy to constantly revise approaches and to modify iteratively the rule sets based on the results generated from the test subsets.
4. As a result of the iterative revision process, the Contractor shall propose a documented set of rules/ clustering methodologies based on the sets defined in Tasks 2 & 3. The rule set can be used for finding commonalities in the selected subset of data and Structure Types. Apply the set of rules to the selected subset of NIST SRO 84 Structure Type data, identify comparable Structure Types that share geometrical and crystallographic commonalities.
5. The Contractor shall report the data, findings, and propose future directions regarding test dataset and descriptors used in the rules, including recommendations for the introduction of further mathematical tools needed for handling necessary data standardization/transformation or statistical data analysis. The Contractor shall also prepare a conference report of findings.
6. The Contractor shall prepare and provide a monthly status report to the Contracting Officer's Representative (COR) and the NIST Subject Matter Expert (NSM E), via e-mail. The report shall include all of the following, at a minimum, relevant to the reporting period: (a) a detailed summary of the work performed on each task; (b) a description of future work to be performed on each task; ( c) delays, reasons for delays, and recommendations brought to the attention of the TOM.

Minimum Requirements:

• PhD. in materials science or related disciplines (inorganic chemistry, physical chemistry, structural chemistry);
• Minimum of five years of experience in crystallographic science and crystallographic data research;
• Demonstrated experience in developing scientific/technical programs for data-management systems and other information systems for the Internet and PC; Visual Basic, FORTRAN, DBMSs, Java.

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