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documentation:optional_materials_keywords

Reference: A RESTful API for exchanging materials data in the AFLOWLIB.org consortium Computational Materials Science, Volume 93, October 2014, Pages 178-192 Richard H. Taylor, Frisco Rose, Cormac Toher, Ohad Levy, Kesong Yang, Marco Buongiorno Nardelli, Stefano Curtarolo http://www.sciencedirect.com/science/article/pii/S0927025614003322

## Bravais_lattice_orig

• Bravais_lattice_orig

Description: Returns the Bravais lattice of the original unrelaxed structure before the calculation.

Type: string

Example: Bravais_lattice_orig=MCLC

Request syntax: $aurl/?Bravais_lattice_orig Tolerance: Calculations of lattices (Brillouin zones), prototypes, and symmetries (point/factor/space groups) are based on different algorithms and require different sets of tolerances. To guarantee self-consistency of the results, initial tolerances are set to very stringent values (e.g., 10-4% for distances, 102% for angles, 10-4% for spectral radii of mapping matrices, etc.) and slowly increased alternatingly (by a factor of 2) until self- consistency is found amongst geometrical descriptors. The final tolerances are usually of the order of ~0.5% for distances and ~1% for angles. ## Bravais_lattice_relax • Bravais_lattice_relax Description: Returns the Bravais lattice of the original relaxed structure after the calculation. Type: string Example: Bravais_lattice_relax=MCLC Request syntax: $aurl/?Bravais_lattice_relax

Tolerance: Calculations of lattices (Brillouin zones), prototypes, and symmetries (point/factor/space groups) are based on different algorithms and require different sets of tolerances. To guarantee self-consistency of the results, initial tolerances are set to very stringent values (e.g., 10-4% for distances, 102% for angles, 10-4% for spectral radii of mapping matrices, etc.) and slowly increased alternatingly (by a factor of 2) until self- consistency is found amongst geometrical descriptors. The final tolerances are usually of the order of ~0:5% for distances and ~1% for angles.

## code

• code

Description: Returns the software name and version used to perform the simulation.

Type: string

Example: code=vasp.4.6.35

## compound

• compound

Description: Similar to composition. Returns the composition description of the compound in the calculated cell.

Type: Set of {string number}

Example: compound=Co2Er6Si6

## dft_type

• dft_type

Description: Returns information about the pseudopotential type, the exchange correlation functional used (normal or hybrid) and use of GW.

Type: Set of strings separated by “,”

Example: If the calculations were performed with VASP, the entry could include “US”, “GGA”, “PAW LDA”, “PAW GGA”, “PAW PBE” , “GW”, “HSE06” (February 2014).

Example: dft_type=PAW_PBE,HSE06

Request syntax: $aurl/?dft_type @article{vasp, author={G. Kresse and J. Furthm\“uller}, title={Efficient iterative schemes for {\it ab initio} total-energy calculations using a plane-wave basis set}, journal=prb,volume={54},pages={11169-11186},year=1996,doi={10.1103/PhysRevB.54.11169}} ## eentropy_cell • eentropy_cell Description: Returns the electronic entropy of the unit cell used to converge the ab initio calculation (smearing). Type: number Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively.

Example: eentropy_cell=0.0011

Request syntax: $aurl/?eentropy_cell ## eentropy_atom • eentropy_atom Description: Returns the electronic entropy of the unit cell used to converge the ab initio calculation (smearing). Type: number Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively.

Example: eentropy_atom=0.0003

## Egap

• Egap

Description: Band gap calculated with the approximations and pseudopotentials described by other keywords. This quantity is determined by tracking the valence band eigenvalue occupancies. For spin-polarized systems, this is the net gap (the gap between the highest occupied state for either spin and the lowest unoccupied state for either spin).

Type: number

Units: eV

Example: Egap=2.5

## energy_cell

• energy_cell

Description: Returns the total ab initio energy of the unit cell E (energy per atom- the value of energy_cell/N).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: energy_cell=-82.1656 Request syntax: $aurl/?energy_cell

## energy_atom

• energy_atom

Description: Returns the total ab initio energy of the unit cell E (energy per atom- the value of energy_cell/N).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: energy_atom=-5.13535 Request syntax: $aurl/?energy_atom

## energy_cutoff

• energy_cutoff

Description: Set of energy cut-o s used during the various steps of the calculations.

Type: Set of strings separated by ”,“;

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: energy_cutoff=384.1,384.1,384.1 Request syntax: $aurl/?energy_cutoff

## enthalpy_cell

• enthalpy_cell

Description: Returns the enthalpy of the system of the unit cell H = E + PV (enthalpy per atom- the value of enthalpy_cell/N).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: enthalpy_cell=-82.1656 Request syntax: $aurl/?enthalpy_cell

## enthalpy_atom

• enthalpy_atom

Description: Returns the enthalpy of the system of the unit cell H = E + PV (enthalpy per atom- the value of enthalpy_cell/N).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: enthalpy_atom=-5.13535 Request syntax: $aurl/?enthalphy_atom

## enthalpy_formation_cell

• enthalpy_formation_cell

Description: Returns the formation enthalpy per unit cell ( per atom). For compounds with atoms per cell, this is defined as: (in the case with and we have ).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: enthalpy_formation_cell=-33.1587 Request syntax: $aurl/?enthalpy_formation_cell

## enthalpy_formation_atom

• enthalpy_formation_atom

Description: Returns the formation enthalpy per unit cell ( per atom). For compounds with atoms per cell, this is defined as: (in the case with and we have ).

Type: number

Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP or QE, respectively. Example: enthalpy_formation_atom=-0.720841 Request syntax: $aurl/?enthalpy_formation_atom

## entropic_temperature

• entropic_temperature

Description: Returns the entropic temperature as defined in Curtarolo et al. and Hart et al. (see reference at top of page) for the structure. The analysis of formation enthalpy is, by itself, insufficient to compare alloy stability at different concentrations and their resilience toward high-temperature disorder. The formation enthalpy represents the ordering-strength of a mixture against decomposition into its pure constituents at the appropriate concentrations . ( is negative for compound forming systems). However, it does not contain information about its resilience against disorder, which is captured by the entropy of the system. To quantify this resilience we define the entropic temperature for each compound as:

where the sign is chosen so that a positive temperature is needed for competing against compound stability. This definition assumes an ideal scenario [9] where the entropy is . is a concentration-maximized formation enthalpy weighted by the inverse of its entropic contribution. Its maximum represents the deviation of a system convex-hull from the purely entropic free-energy hull, , and hence the ability of its ordered phases to resist the temperature-driven deterioration into a disordered mixture exclusively promoted by configurational-entropy.

Type: number

Units: Kelvin

Example: entropic_temperature=1072.1

Description: Once the ”files“ list has been parsed, each file can be accessed with $aurl/file (note no ”?“ for accessing individual files). ## forces • forces Description: Final quantum mechanical forces (Fi; Fj; Fk) in the notation of the code. Type: Triplets (number,number,number) separated by ”;“ for each atom in the unit cell Units: Natural units of the $code, e.g., eV/Å or a.u. if the calculations were performed with VASP or QE, respectively.

Example: forces=0,-0.023928,0.000197;0,0.023928,-0.000197;…

Request syntax: $aurl/?forces ## geometry • geometry Description: Returns geometrical data describing the unit cell in the usual notation, where . Type: Sixtuplet (number,number,number,number,number,number) Units: a, b, c are the natural units of the $code, e.g., Å or a.u. (Bohr) if the calculations were performed with VASP or QE, respectively. α, β, γ are in degrees.

Example: geometry=18.82,18.82,18.82,32.41,32.41,32.41

## lattice_variation_orig

• lattice_variation_orig

Description: Return the lattice system and lattice variation (Brillouin zone) of the original-unrelaxed structure before the calculation.

Type: string

Example: lattice_variation_orig=RHL1

## lattice_variation_relax

• lattice_variation_relax

Description: Return the lattice system and lattice variation (Brillouin zone) of the relaxed structure after the calculation.

Type: string

Example: lattice_variation_relax=MCLC1

## ldau_TLUJ

• ldau_TLUJ

Description: This vector of numbers contains the parameters of the “DFT+U” calculations, based on a corrective functional inspired by the Hubbard model[13,?]. Standard values in the AFLOWLIB.org library come from Refs. [8, 14]. There are four fields (T;{L};{U};{J}), separated by ”;“. The first field indicates the type (T) of the DFT+U corrections: type=1, the rotationally invariant version introduced by Liechtenstein et al. [15]; type=2, the simplified rotationally invariant version introduced by Dudarev et al. [16]. The second field indicates the l-quantum number ({L}, one number for each species separated by ”,“) for which the on-site interaction is added (-1=neglected, 0=, 1=, 2=, 3=). The third field lists the effective on-site Coulomb interaction parameters ({U}, one number for each species separated by ”,“). The fourth field species the effective on-site exchange interaction parameters ({J}, one number for each species separated by ”,“). Although more compact, the convention is similar to the VASP notation [6].

Type: number;{number };{number }{number }

Example: ldau_TLUJ=2;2,0,0;5,0,0;0,0,0

## nbondxx

• nbondxx

Description: Nearest neighbors bond lengths of the relaxed structure per ordered set of species . For pure systems: ; for binaries: ; for ternaries: and so on.

Type: Set of numbers

Units: Natural units of the $code, e.g., Å or a.u. (Bohr) if the calculations were performed with VASP [6] or QE [7], respectively. Example: nbondxx=1.2599,1.0911,1.0911,1.7818,1.2599,1.7818 (for a three species entry) Request syntax: $aurl/?nbondxx

## nspecies

• nspecies

Description: Returns the number of species in the system (e.g., binary = 2, ternary = 3, etc.).

Type: number

Example: nspecies=3

Request syntax: $aurl/?nspecies ## Pearson_symbol_orig • Pearson_symbol_orig Description: Returns the Pearson symbol of the original-unrelaxed structure before the calculation. Type: string Example: Pearson_symbol_orig=mS32 Request syntax: $aurl/?Pearson_symbol_orig

Tolerance: See discussion about tolerances in entry Bravais_lattice_orig.

## Pearson_symbol_relax

• Pearson_symbol_relax

Description: Returns the Pearson symbol of the relaxed structure after the calculation.

Type: string

Example: Pearson_symbol_relax=mS32

## positions_fractional

• positions_fractional

Description: Final fractional positions with respect to the unit cell as specified in $geometry. Type: Triplets (number,number,number) separated by ”;“ for each atom in the unit cell Example: positions_fractional=0,0,0;0.25,0.25,0.25;… Request syntax: $aurl/?positions_fractional

## pressure

• pressure

Description: Returns the external pressure selected for the simulation.

Type: number

Units: Natural units of the $code, e.g., kbar or a.u. (Ry/Bohr) if the calculations were performed with VASP [6] or QE [7], respectively. Example: pressure=10.0 Request syntax: $aurl/?pressure

## prototype

• prototype

Description: Returns the AFLOW unrelaxed prototype which was used for the calculation. The list can be accessed with the command \aflow –protos or by consulting the online links. The options are illustrated in the AFLOW manual. Note that during the calculation, unstable structures can deform and lead to different relaxed configurations. It is thus imperative for the user to make an elaborate analysis of the final structure to pinpoint the right prototype to report. Differences in Bravais lattices,

Type: string

Example: prototype=T0001.A2BC

Request syntax: $aurl/?prototype Tolerance: See discussion about tolerances in entry Bravais_lattice_orig. ## PV_cell • PV_cell Description: Pressure multiplied by volume of the unit cell. Type: number Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP [6] or QE [7], respectively.

Example: PV_cell=12.13

Request syntax: $aurl/?PV_cell ## PV_atom • PV_atom Description: Pressure multiplied by volume of the atom. Type: number Units: Natural units of the $code, e.g., eV or Ry (eV/atom or Ry/atom) if the calculations were performed with VASP [6] or QE [7], respectively.

Example: PV_atom=3.03

## sg (sg2)

• sg (sg2)

Description: Evolution of the space group of the compound. The first, second and third string represent space group name/number before the first, after the first, and after the last relaxation of the calculation.

Tolerance: sg values are calculated with 3.0% and 0.5 deg tolerances for lengths and angles, respectively. (sg2 is with 1.5% and 0.25 deg). Symmetry is cross validated through the internal engines of AFLOW, PLATON, and FINDSYM.

Type: Triplet string,string,string

Example: sg=Fm-3m#225,Fm-3m#225,Fm-3m#225 (sg2=R-3c #167,R-3c #167,R-3c #167)

Request syntax: $aurl/?sg ($aurl/?sg2)

## spacegroup_orig

• spacegroup_orig

Description: Returns the spacegroup number of the original-unrelaxed structure before the calculation.

Tolerance: Same as sg.

Type: number

Example: spacegroup_orig=225

## species

• species

Description: Species of the atoms.

Type: List of strings separated by ”,“

Example: species=Y,Zn,Zr,

## species_pp_version

• species_pp_version

Description: Pseudopotential versions.

Type: List of strings separated by ”,“

Example: species_pp_version=Y_sv:PAW_PBE:06Sep2000,Zn:PAW_PBE:06Sep2000,Zr_sv:PAW_PBE:07Sep2000

Request syntax: $aurl/?species_pp_version ## spin_cell • spin_cell Description: For spin polarized calculations, the total magnetization of the cell. Type: number Units: Natural units of the $code, e.g., (Bohr magneton).

Example: spin_cell=2.16419

Request syntax: $aurl/?spin_cell ## spin_atom • spin_atom Description: For spin polarized calculations, the total magnetization per atom. Type: number Units: Natural units of the $code, e.g., (Bohr magneton).

Example: spin_atom=0.541046

Request syntax: $aurl/?spin_atom ## spinD • spinD Description: For spin polarized calculations, the spin decomposition over the atoms of the cell. Type: List of numbers separated by ”,“ Units: Natural units of the $code, e.g., (Bohr magneton).

Example: spinD=0.236,0.236,-0.023,1.005

Request syntax: $aurl/?spinD ## spinD_magmom_orig • spinD_magmom_orig Description: For spin polarized calculations, string containing the values used to initialize the magnetic state for the ab initio calculation. Type: String containing the instruction passed to the ab initio code with spaces substituted by “_” Units: Natural units of the $code.

Example: spinD_magmom_orig=+5_-5_+5_-5

Request syntax: $aurl/?spinD_magmom_orig ## spinF • spinF Description: For spin polarized calculations, the magnetization of the cell at the Fermi level. Type: number Units: Natural units of the $code, e.g., (Bohr magneton).

Example: spinF=0.410879

## valence_cell_std

• valence_cell_std

Description: Returns standard valence.

Type: number

Example: valence_cell_std=22

## volume_cell (volume_atom)

• volume_cell (volume_atom)

Description: Returns the volume of the unit cell (per atom in the unit cell).

Type: number

Units: Natural units of the $code, e.g., Å3 3 or Bohr33/atom or Bohr3/atom) if the calculations were per- formed with VASP [6] or QE [7], respectively. Example: volume_cell=100.984 (volume_atom=25.2461) Request syntax: $aurl/?volume_cell (\$aurl/?volume_atom)