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
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
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
Description: Returns the software name and version used to perform the simulation.
Type: string
Example: code=vasp.4.6.35
Request syntax: $aurl/?code
composition
Description: Returns a comma delimited composition description of the structure entry in the calculated cell.
Type: List of number
separated by “,”
Example: composition=2,6,6
(For a A2B6C6 compound.)
Request syntax: $aurl/?composition
compound
Description: Similar to composition
. Returns the composition description of the compound in the calculated cell.
Type: Set of {string number}
Example: compound=Co2Er6Si6
Request syntax: $aurl/?compound
density
Description: Returns the mass density.
Type: number
Units: grams/cm3
Example: density=7.76665
Request syntax: $aurl/?density
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
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
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
Request syntax: $aurl/?eentropy_atom
Efermi
Description: Fermi energy of the system.
Type: number
Units: eV
Example: Efermi=-4.5
Request syntax: $aurl/?Efermi
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
Request syntax: $aurl/?Egap
Egap_type
Description: Given a band gap, this keyword describes if the system is a metal, a semi-metal, an insulator with direct or indirect band gap.
Type: string
Example: Egap_type=insulator_direct
Request syntax: $aurl/?Egap_type
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
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
Description: Set of energy cut-os 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
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
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
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
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
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
Request syntax: $aurl/?entropic_temperature
files
Description: Provides access to the input and output les used in the simulation (provenance data).
Type: List of strings
separated by ”,“
Example: files=Bi_dRh_pv.33.cif,Bi_dRh_pv.33.png,CONTCAR.relax,CONTCAR.relax1…,
DOSCAR.static.bz2,EIGENVAL.bands.bz2,KPOINTS.bands.bz2,aflow.in,edata.bands.out,…
edata.orig.out,edata.relax.out,…
Request syntax: $aurl/?files
Description: Once the ”files
“ list has been parsed, each file can be accessed with $aurl/file
(note no ”?“
for accessing individual files).
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
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
Request syntax: $aurl/?geometry
lattice_system_orig
Description: Return the lattice system and lattice variation (Brillouin zone) of the original-unrelaxed structure before the calculation.
Type: string
Example: lattice_system_orig=rhombohedral
Request syntax: $aurl/?lattice_system_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
Request syntax: $aurl/?lattice_variation_orig
lattice_system_relax
Description: Return the lattice system and lattice variation (Brillouin zone) of the relaxed structure after the calculation.
Type: string
Example: lattice_system_relax=monoclinic
Request syntax: $aurl/?lattice_system_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
Request syntax: $aurl/?lattice_variation_relax
kpoints
Description: Set of k-point meshes uniquely identifying the various steps of the calculations, e.g.\ relaxation, static and electronic band structure (specifying the k-space symmetry points of the structure).
Type: Set of numbers
and strings
separated by ”,“ and ”;“
Example: kpoints=10,10,10;16,16,16;G-X-W-K-G-L-U-W-L-K+U-X
Request syntax: $aurl/?kpoints
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].
Units: a-dimensional; {adimensional}; {eV}; {eV}
Type: number
;{number
};{number
}{number
}
Example: ldau_TLUJ=2;2,0,0;5,0,0;0,0,0
Request syntax: $aurl/?ldau_TLUJ
natoms
Description: Returns the number of atoms in the unit cell of the structure entry. The number can be non integer if partial occupation is considered within appropriate approximations.
Type: number
Example: natoms=12
Request syntax: $aurl/?natoms
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
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
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
Description: Returns the Pearson symbol of the relaxed structure after the calculation.
Type: string
Example: Pearson_symbol_relax=mS32
Request syntax: $aurl/?Pearson_symbol_relax
Tolerance: See discussion about tolerances in entry Bravais_lattice_orig
.
positions_cartesian
Description: Final Cartesian positions in the notation of the code.
Type: Triplets (number,number,number
) separated by ”;“ for each atom in the unit cell
Example: positions_cartesian=0,0,0;18.18438,0,2.85027;…
Request syntax: $aurl/?positions_cartesian
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
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
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
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
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
Request syntax: $aurl/?PV_atom
scintillation_attenuation_length
Description: Returns the scintillation attenuation length of the compound in cm. See Refs. [8, 18].
Type: real number
Example: scintillation_attenuation_length=2.21895
Request syntax: $aurl/?scintillation_attenuation_length
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
Description: Returns the spacegroup number of the original-unrelaxed structure before the calculation.
Tolerance: Same as sg
.
Type: number
Example: spacegroup_orig=225
Request syntax: $aurl/?spacegroup_orig
spacegroup_relax
Description: Returns the spacegroup number of the relaxed structure after the calculation.
Tolerance: Same as sg
.
Type: number
Example: spacegroup_relax=225
Request syntax: $aurl/?spacegroup_relax
species
Description: Species of the atoms.
Type: List of strings
separated by ”,“
Example: species=Y,Zn,Zr,
Request syntax: $aurl/?species
species_pp
Description: Pseudopotentials species.
Type: List of strings
separated by ”,“
Example: species_pp=Y_sv,Zn,Zr_sv,
Request syntax: $aurl/?species_pp
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
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
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
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
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
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
Request syntax: $aurl/?spinF
stoichiometry
Description: Similar to composition, returns a comma delimited stoichiometry description of the structure entry in the calculated cell.
Type: List of number
separated by ”,“
Example: stoichiometry=0.5,0.25,0.25
Request syntax: $aurl/?stoichiometry
valence_cell_std
Description: Returns standard valence.
Type: number
Example: valence_cell_std=22
Request syntax: $aurl/?valence_cell_std
valence_cell_iupac
Description: Returns IUPAC valence, the maximum number of univalent atoms that may combine with the atoms.
Type: number
Example: valence_cell_iupac=12
Request syntax: $aurl/?valence_cell_iupac
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 Bohr3 (Å3/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)