Property Reference

Meaning, units and physical significance of every material-data field

Basic Information

Material identification and fundamental crystallographic parameters. These fields come from the Materials Project summary data.

Field	Label	Type	Unit	Description
formula	Chemical Formula	string	-	Chemical formula of the material, composed of element symbols and atomic ratios (e.g. Fe100Cr)
mp_id	MP-ID	string	-	Materials Project unique identifier (e.g. mp-2866)
nelements	Elements	int	-	Number of distinct chemical elements in the material
nsites	Sites	int	-	Total number of atomic sites in the unit cell
density	Density	float	g/cm³	Mass density of the material
volume	Volume	float	Å³	Total volume of the unit cell
a, b, c	Cell Parameters a, b, c	float	Å	Lengths of the three cell basis vectors
alpha, beta, gamma	Cell Angles α, β, γ	float	°	Angles between the three cell basis vectors
crystal_system	Crystal System	string	-	One of the seven crystal systems: Cubic / Tetragonal / Orthorhombic / Hexagonal / Trigonal / Monoclinic / Triclinic
Bravais_Lattice	Bravais Lattice	string	-	Bravais lattice type (e.g. Im-3m), combined with space-group information
point_group	Point Group	string	-	Crystallographic point group of the material (e.g. m-3m)
packing_fraction	Packing Fraction	float	-	Fraction of the unit-cell volume filled by atoms (0–1)

Energy Properties

Energy parameters describing the thermodynamic stability of the material. A negative formation energy usually indicates thermodynamic stability.

Field	Label	Type	Unit	Description
formation_energy_per_atom	Formation Energy/atom	float	eV/atom	Formation energy: energy required per atom to synthesize the material from the elemental standard states. A negative value indicates thermodynamic stability
energy_per_atom	Energy/atom	float	eV/atom	Total DFT-calculated energy divided by the number of atoms
energy_above_hull	Energy above Hull	float	eV/atom	Energy distance of the material above the convex hull of the phase diagram. 0 means a stable phase; larger values mean less stable
uncorrected_energy_per_atom	Uncorrected Energy	float	eV/atom	Raw DFT energy without energy corrections
volume_per_atom	Volume/atom	float	Å³	Average volume occupied per atom
c_over_a	c/a Ratio	float	-	Ratio of cell parameters c to a, used to assess lattice distortion

Electronic Properties

Parameters describing the electronic structure of the material, including metallicity and band gap.

Field	Label	Type	Unit	Description
is_metal	Metallic	bool	-	Whether the material is a metal. Metals have electronic states at the Fermi level and no band gap
band_gap	Band Gap	float	eV	Energy difference between the valence-band top and the conduction-band bottom. 0 means a metal
is_gap_direct	Direct Gap	bool	-	Whether the band gap is direct. For direct-gap materials the valence-band top and conduction-band bottom are at the same position in k-space
cbm	CBM	float	eV	Conduction Band Minimum: the lowest conduction-band energy relative to the Fermi level

Magnetic Properties

Magnetic properties of the material, including total magnetic moment and magnetic-ordering type.

Field	Label	Type	Unit	Description
is_magnetic	Magnetic	bool	-	Whether the material is magnetic
total_magnetization	Total Mag. Moment	float	μB	Total magnetic moment of the unit cell (Bohr magnetons)
ordering	Mag. Ordering	string	-	Magnetic-ordering type: FM (ferromagnetic) / AFM (antiferromagnetic) / NM (non-magnetic)
num_magnetic_sites	Mag. Sites	int	-	Number of atomic sites in the unit cell with a significant localized magnetic moment
total_mag_norm_vol	Magnetization/Volume	float	μB/Å³	Magnetization per unit volume

Elastic Properties

Mechanical parameters of the material, computed from the elastic-constant tensor. Based on Voigt-Reuss-Hill (VRH) averaging.

Field	Label	Type	Unit	Description
k_vrh	K_VRH (Bulk Modulus)	float	GPa	Bulk Modulus VRH average; measures the resistance of the material to volume compression
g_vrh	G_VRH (Shear Modulus)	float	GPa	Shear Modulus VRH average; measures the resistance of the material to shear deformation
E_Calc(GPa)	Young's Modulus E	float	GPa	Young's Modulus, computed from K and G: E = 9KG/(3K+G)
homogeneous_poisson	Poisson Ratio ν (VRH)	float	-	Homogeneous Poisson Ratio, VRH-averaged; ratio of transverse to longitudinal deformation. Typically 0–0.5
Pugh_Ratio(K/G)	Pugh Ratio K/G	float	-	Pugh ductility indicator. >1.75 indicates a ductile material, <1.75 a brittle one
Vickers_Hard_Est(GPa)	Vickers Hardness Est.	float	GPa	Vickers hardness estimated from the elastic moduli
Ductility	Ductility	string	-	Ductile/brittle classification label
universal_anisotropy	Anisotropy	float	-	Universal Anisotropy Index; 1 means isotropic, larger values mean stronger anisotropy
Lame_Lambda(GPa)	Lamé λ	float	GPa	First Lamé parameter, related to the bulk and shear moduli
bulk_modulus	Bulk Modulus	float	GPa	Provided by the ELA dataset only; same origin as K_VRH
shear_modulus	Shear Modulus	float	GPa	Provided by the ELA dataset only; same origin as G_VRH
debye_temperature	Debye Temperature	float	K	Provided by the ELA dataset only; Debye temperature estimated from the elastic moduli and density
sound_velocity	Mean Sound Velocity	float	m/s	Mean sound velocity, provided by the ELA dataset only
homogeneity	Homogeneity	float	-	Elastic homogeneity index, provided by the ELA dataset only

Data Sources

All material data comes from the following authoritative databases:

Materials Project

DFT-based materials computation database, providing structure, energy, elasticity and other data

NIST JARVIS

Materials database of the U.S. National Institute of Standards and Technology (authentication required)

NIMS DICE

Materials information database of Japan's National Institute for Materials Science (authentication required)

When using the databases of these institutions, please comply with their respective data-use terms, copyright and disclaimers. The full agreement texts and attribution requirements of each source institution are on the Legal Information / Data Use Terms page.

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