Input Reference Essential

This input reference lists the elements and attributes available to define an input for an exciting calculation. The input file is named input.xml it must be a valid XML file and it must contain the root element input .

Unless explicitly stated otherwise, exciting uses atomic units. In this system $\hbar=1$, the electron mass $m=1$, the Bohr radius $a_0=1$and the electron charge $e=1$(note that the electron charge is positive, so that the atomic numbers $Z$are negative). Thus, the atomic unit of length is 0.52917720859(36) ${\buildrel _{\circ} \over {\mathrm{A}}}$, and the atomic unit of energy is the Hartree which equals 27.21138386(68) eV. The unit of the external magnetic fields is defined such that one unit of magnetic field equals 1717.2445320376 Tesla.

Element: input

The input element is the root element of the exciting input file. The input element must contain one structure element and one groundstate element.

Find a minimal input file instance described here.

contains: title (1 times)
structure (1 times)
groundstate (optional)
structureoptimization (optional)
properties (optional)
XPath: /input

Element: title

Title of the input file.

Type: string
XPath: /input/title

Element: structure

The structure element contains all structural information such as unit cell and atom positions.

contains: crystal (1 times)
species (zero or more)
XPath: /input/structure

This element allows for specification of the following attributes:

Attribute: speciespath

Gives the path to the directory containing the species files. It can be an HTTP URL too (needs wget ).

Type: anyURI
Use: required
XPath: /input/structure/@speciespath

Element: crystal

The crystal element defines the unit cell of the calculation.

contains: basevect (3 times)
XPath: /input/structure/crystal

This element allows for specification of the following attributes:

Attribute: scale

The attribute scale scales all the lattice vectors. This is useful for varying the volume.

Type: fortrandouble
Default: "1.0d0"
Use: optional
Unit: 1
XPath: /input/structure/crystal/@scale

Attribute: stretch

Allows for a separate scaling of each lattice vector. "1 1 1" means no scaling.

Type: vect3d
Default: "1.0d0 1.0d0 1.0d0 "
Use: optional
XPath: /input/structure/crystal/@stretch

Element: basevect

The basevect element defines one basis vector.

Type: vect3d
Unit: Bohr
XPath: /input/structure/crystal/basevect

Element: species

The species element defines the atom species. It contains a atom element for each atom of the species.

contains: atom (1 times or more)
XPath: /input/structure/species

This element allows for specification of the following attributes:

Attribute: href

Type: anyURI
Default: ""
Use: optional
XPath: /input/structure/species/@href

Attribute: speciesfile

Defines the file from which the species definition is read. It is looked up in the species directory specified by the species path.

Type: anyURI
Use: required
XPath: /input/structure/species/@speciesfile

Element: atom

The atom element carries all the attributes of a single atom in the unit cell. The position is given by the coord attribute

Type: no content
XPath: /input/structure/species/atom

This element allows for specification of the following attributes:

Attribute: coord

Position in lattice coordinates.

Type: vect3d
Use: required
Unit: lattice coordinates
XPath: /input/structure/species/atom/@coord

Element: groundstate

The groundstate element is required for anny calculation. Its attributes are the parameters and methods used to calculate the groundstate density.

contains: spin (optional)
XPath: /input/groundstate

This element allows for specification of the following attributes:

Attribute: do

Decides if the groundstate is skipped or recalculated or continued from file.

Type: choose from:
fromscratch
fromfile
skip
Default: "fromscratch"
Use: optional
XPath: /input/groundstate/@do

Attribute: epspot

If the RMS change in the effective potential and magnetic field is smaller than epspot , then the self-consistent loop is considered converged and exited. For structural optimization runs this results in the forces being calculated, the atomic positions updated and the loop restarted. See also maxscl.

Type: fortrandouble
Default: "1.0d-6"
Use: optional
XPath: /input/groundstate/@epspot

Attribute: maxscl

Upper limit for te selfconsistency loop.

Type: integer
Default: "200"
Use: optional
XPath: /input/groundstate/@maxscl

Attribute: mixer

select the mixing (relaxation) scheme for SCF

Type: choose from:
lin
msec
pulay
Default: "msec"
Use: optional
XPath: /input/groundstate/@mixer

Attribute: ngridk

Number of k grid points along the basis vector directions.

Type: integertriple
Use: required
XPath: /input/groundstate/@ngridk

Attribute: reducek

If the attribute reducek is "true" the $k$-point set is reduced with the crystal symmetries.

Type: boolean
Default: "true"
Use: optional
XPath: /input/groundstate/@reducek

Attribute: rgkmax

This sets the maximum length for the ${ \bf G}+{ \bf k}$vectors, defined as rgkmax divided by the smallest muffin-tin radius.

Type: fortrandouble
Default: "7.0d0"
Use: optional
XPath: /input/groundstate/@rgkmax

Attribute: stype

A smooth approximation to the Dirac delta function is needed to compute the occupancies of the Kohn-Sham states. The attribute swidth determines the width of the approximate delta function.

Type: choose from:
Gaussian
Methfessel-Paxton 1
Methfessel-Paxton 2
Fermi Dirac
Square-wave impulse
Default: "Gaussian"
Use: optional
XPath: /input/groundstate/@stype

Attribute: swidth

Width of the smooth approximation to the Dirac delta function.

Type: fortrandouble
Default: "0.001d0"
Use: optional
XPath: /input/groundstate/@swidth

Attribute: tforce

Decides if the force should be calculated at the end of the self-consistent cycle.

Type: boolean
Default: "false"
Use: optional
XPath: /input/groundstate/@tforce

Attribute: xctype

Type of exchange-correlation functional to be used

  • No exchange-correlation funtional ( $E_{\rm xc}\equiv 0$)
  • LDA, Perdew-Zunger/Ceperley-Alder, Phys. Rev. B 23 , 5048 (1981)
  • LSDA, Perdew-Wang/Ceperley-Alder, Phys. Rev. B 45 , 13244 (1992)
  • LDA, X-alpha approximation, J. C. Slater, Phys. Rev. 81 , 385 (1951)
  • LSDA, von Barth-Hedin, J. Phys. C 5 , 1629 (1972)
  • GGA, Perdew-Burke-Ernzerhof, Phys. Rev. Lett. 77 , 3865 (1996)
  • GGA, Revised PBE, Zhang-Yang, Phys. Rev. Lett. 80 , 890 (1998)
  • GGA, PBEsol, arXiv:0707.2088v1 (2007)
  • GGA, Wu-Cohen exchange (WC06) with PBE correlation, Phys. Rev. B 73 , 235116 (2006)
  • GGA, Armiento-Mattsson (AM05) spin-unpolarised functional, Phys. Rev. B 72 , 085108 (2005)
Type: choose from:
LDAPerdew-Zunger
LSDAPerdew-Wang
LDA-X-alpha
LSDA-Barth-Hedin
GGAPerdew-Burke-Ernzerhof
GGArevPBE
GGAPBEsol
GGA-Wu-Cohen
GGAArmiento-Mattsson
EXX
none
Default: "LSDAPerdew-Wang"
Use: optional
XPath: /input/groundstate/@xctype

Element: spin

If the spin element is present calculation is done with spin polarization.

Type: no content
XPath: /input/groundstate/spin

This element allows for specification of the following attributes:

Attribute: bfieldc

Alows to apply a constant B field This is a constant magnetic field applied throughout the entire unit cell and enters the second-variational Hamiltonian as

(1)
\begin{align} \frac{g_e\alpha}{4}\,\vec{\sigma}\cdot{\bf B}_{\rm ext}, \end{align}

where $g_e$is the electron $g$-factor (2.0023193043718). This field is normally used to break spin symmetry for spin-polarised calculations and considered to be infinitesimal with no direct contribution to the total energy. In cases where the magnetic field is finite (for example when computing magnetic response) the external ${ \bf B}$-field energy reported in INFO.OUT should be added to the total by hand. This field is applied throughout the entire unit cell. To apply magnetic fields in particular muffin-tins use the bfcmt vect ors in the atoms block. Collinear calculations are more efficient if the field is applied in the $z$-direction.

Type: vect3d
Default: "0.0d0 0.0d0 0.0d0 "
Use: optional
XPath: /input/groundstate/spin/@bfieldc

Attribute: fixspin

Type: choose from:
none
total FSM
localmt FSM
both
Default: "none"
Use: optional
XPath: /input/groundstate/spin/@fixspin

Attribute: momfix

The desired total moment for a FSM calculation.

Type: vect3d
Default: "0.0d0 0.0d0 0.0d0"
Use: optional
XPath: /input/groundstate/spin/@momfix

Attribute: spinorb

If spinorb is "true" , then a $\boldsymbol \sigma\cdot{ \bf L}$term is added to the second-variational Hamiltonian.

Type: boolean
Use: optional
XPath: /input/groundstate/spin/@spinorb

Element: structureoptimization

The structure optimization element triggers if present a geometry relaxation.

Type: no content
XPath: /input/structureoptimization

This element allows for specification of the following attributes:

Attribute: epsforce

Convergence tolerance for the forces during a structural optimization run.

Type: fortrandouble
Default: "5.0d-5"
Use: optional
XPath: /input/structureoptimization/@epsforce

Attribute: resume

Resumption of structural optimization run using density in STATE.OUT but with positions from input.xml .

Type: boolean
Default: "false"
Use: optional
XPath: /input/structureoptimization/@resume

Element: properties

Properties listed in this element can be calculated from the groundstate. It works also from a saved state from a previous run.

contains: bandstructure (optional)
dos (optional)
chargedensityplot (optional)
fermisurfaceplot (optional)
XPath: /input/properties

Element: bandstructure

If present a banstructure is calculated.

contains: plot1d
XPath: /input/properties/bandstructure

This element allows for specification of the following attributes:

Attribute: scissor

Value to shift bandgap.

Type: fortrandouble
Default: "0.0d0"
Use: optional
Unit: Hartree
XPath: /input/properties/bandstructure/@scissor

Element: dos

If present a DOS calculation is started.

DOS and optics plots require integrals of the kind

(2)
\begin{align} g(\omega_i)=\frac{\Omega}{(2\pi)^3}\int_{\rm BZ} f({ \bf k}) \delta(\omega_i-e({\bf k}))d{ \bf k}. \end{align}

These are calculated by first interpolating the functions $e({ \bf k})$and $f({ \bf k})$with the trilinear method on a much finer mesh whose size is determined by ngrdos . Then the $\omega$-dependent histogram of the integrand is accumulated over the fine mesh. If the output function is noisy then either ngrdos should be increased or nwdos decreased. Alternatively, the output function can be artificially smoothed up to a level given by nsmdos . This is the number of successive 3-point averages to be applied to the function $g$.

Type: no content
XPath: /input/properties/dos

This element allows for specification of the following attributes:

Attribute: ngrdos

Effective k-point mesh size to be used for Brillouin zone integration.

Type: integer
Default: "100"
Use: optional
XPath: /input/properties/dos/@ngrdos

Attribute: nwdos

Number of frequency/energy points in the DOS

Type: integer
Default: "500"
Use: optional
XPath: /input/properties/dos/@nwdos

Attribute: scissor

Type: fortrandouble
Default: "0.0d0"
Use: optional
Unit: Hartree
XPath: /input/properties/dos/@scissor

Element: chargedensityplot

Plot the charge density

contains: plot1d (optional)
plot2d (optional)
plot3d (optional)
XPath: /input/properties/chargedensityplot

Element: fermisurfaceplot

Writes Fermi surface data to file.

Type: no content
XPath: /input/properties/fermisurfaceplot

This element allows for specification of the following attributes:

Attribute: nstfsp

Number of states to be included in the Fermi surface plot file.

Type: integer
Default: "6"
Use: optional
XPath: /input/properties/fermisurfaceplot/@nstfsp

Attribute: separate

Type: boolean
Use: optional
XPath: /input/properties/fermisurfaceplot/@separate

+ Reused Elements
The following elements can occur more than once in the input file. There for they are listed separately.

Element: origin

Type: no content
XPath: ./origin
Parent: ./plot2d/parallelogram
./plot3d/box

This element allows for specification of the following attributes:

Attribute: coord

Type: vect3d
Use: optional
XPath: ./origin/@coord

Element: point

Type: no content
XPath: ./point
Parent: ./plot1d/path
./plot2d/parallelogram
./plot3d/box

This element allows for specification of the following attributes:

Attribute: coord

Type: vect3d
Use: required
XPath: ./point/@coord

Attribute: label

Type: string
Default: ""
Use: optional
XPath: ./point/@label

Element: plot1d

The element plot1d specifies sample points along a path. The coordinate space (lattice or cartesian)is chosen in the context of the parent.

contains: path (1 times)
XPath: ./plot1d
Parent: /input/properties/bandstructure
/input/properties/chargedensityplot

Element: path

contains: point (2 times or more)
XPath: ./plot1d/path

This element allows for specification of the following attributes:

Attribute: steps

Type: integer
Use: required
XPath: ./plot1d/path/@steps

Element: plot2d

Defines a 2d plot domain.

contains: parallelogram (1 times)
XPath: ./plot2d
Parent: /input/properties/chargedensityplot

Element: parallelogram

contains: origin (1 times)
point (2 times)
XPath: ./plot2d/parallelogram

This element allows for specification of the following attributes:

Attribute: grid

Type: integerpair
Use: required
XPath: ./plot2d/parallelogram/@grid

Element: plot3d

Defines a 3d plot domain.

contains: box (1 times)
XPath: ./plot3d
Parent: /input/properties/chargedensityplot

Element: box

contains: origin (1 times)
point (3 times)
XPath: ./plot3d/box

This element allows for specification of the following attributes:

Attribute: grid

Type: integertriple
Use: required
XPath: ./plot3d/box/@grid

Element: pointstatepair

The element pointstatepair defines a ${ \bf k}$-point and state index pair.

Type: integerpair
XPath: ./pointstatepair
Parent: ./kstlist

Element: kstlist

The kstlist element is used in the LSJ and wavefunction plot element This is a user-defined list of ${ \bf k}$-point and state index pairs which are those used for plotting wavefunctions and writing ${ \bf L}$, ${ \bf S}$and ${ \bf J}$expectation values.

contains: pointstatepair (1 times or more)
XPath: ./kstlist
Parent:

Data Types

The Input definition uses derived data types. These are described here.

Type fortrandouble

The Type fortrandouble allows to use the letters "eEdDqQ" for exponent operators. This alters in what precision the number is parsed.

Type vector

A vector is a space separated list of floating point numbers.

Example: "1.3 2.3e4 3 90"

Type integerlist

List of space separated integers.

Type vect3d

Three dimensional vector as three space separated floating point numbers.

Type vect2d

Three dimensional vector as three space separated floating point numbers.

Type integertriple

Space separated list of three integers.

Example: "1 2 3"

Type integerpair

Space separated list of two integers

Example: "1 2"

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