Imagine being a materials scientist searching for a new material with specific optical or electronic properties. Traditionally, this would involve sifting through thousands of research papers or conducting extensive laboratory experiments. But what if there were a comprehensive database providing verified computational data on materials—including crystal structures, electronic properties, and optical characteristics? The Materials Project is precisely such a platform, offering researchers a powerful tool to accelerate discovery. This article delves into a case study from the database: orthorhombic barium chloride (BaCl₂).
BaCl₂: A Versatile Chemical Compound
Barium chloride (BaCl₂) is a widely used chemical compound in both laboratory and industrial settings. It appears as colorless crystals, is highly soluble in water, and exhibits moderate toxicity. In materials science, BaCl₂ serves as a precursor for synthesizing other barium-based compounds. Its unique crystal structure and optical properties also make it a subject of intrinsic research interest.
BaCl₂ in the Materials Project Database
The Materials Project database (entry ID: mp-23199) provides detailed computational data on BaCl₂, including its crystal structure, electronic properties, and optical behavior. Below, we analyze key features from this entry.
1. Crystal Structure
At standard conditions, BaCl₂ adopts an orthorhombic crystal structure with space group Pnma (62). This structure features three mutually perpendicular axes (a, b, c) and specific symmetry operations. The unit cell parameters are:
- a = 4.77 Å
- b = 7.92 Å
- c = 9.52 Å
- Angles (α, β, γ) = 90°
- Volume = 359.81 ų
The database also provides fractional coordinates for atoms within the unit cell:
Barium (Ba):
4c Wyckoff position at (¼, 0.248672, 0.882972)
Chlorine (Cl):
Two 4c positions at (¼, 0.028387, 0.170834) and (¾, 0.356327, 0.070447)
Wyckoff positions denote symmetry-equivalent atomic sites. The coordinates describe each atom’s relative location within the unit cell—for example, barium resides at one-quarter of the a-axis length.
2. Crystallographic Details
- Crystal system: Orthorhombic
- Space group symbol: Pnma
- Point group: mmm
- Density: 3.84 g/cm³
- Oxidation states: Ba²⁺, Cl⁻
3. Coordination Environment
Barium ions in BaCl₂ are coordinated by nine chlorine atoms, forming a three square-face-capped trigonal prism (TPRS-9 geometry). The continuous symmetry measure (CSM) of 1.123 indicates close alignment with an ideal polyhedron.
4. Electronic and Optical Properties
- Band structure: Visualizations show electron energy distributions, informing conductivity and light absorption.
- Bandgap: The GGA-calculated bandgap determines the energy threshold for electronic transitions, influencing optical absorption ranges.
- Optical metrics: Absorption coefficients, dielectric functions, and reflectivity data predict interaction with electromagnetic radiation.
5. Transport Properties
Effective masses of electrons and holes quantify charge carrier mobility, with lower values indicating better conductivity.
6. Additional Metrics
- Energy above convex hull (synthetic stability)
- Predicted melting point
- Synthesis status (experimentally verified or predicted)
The Value of the Materials Project
This platform empowers researchers by:
- Accelerating material searches through centralized data
- Enabling property predictions to guide experiments
- Facilitating discovery of novel materials via computational screening
Conclusion
The Materials Project exemplifies how computational materials science can transform research workflows. By analyzing BaCl₂’s structural and electronic profiles, scientists gain insights that would otherwise require extensive experimentation. This case study underscores the database’s role in advancing materials innovation.