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)

$\frac{g_e\alpha}{4}\,\vec{\sigma}\cdot{\bf B}_{\rm ext},$

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)

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

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"

atom		/input/structure/species/atom
bandstructure		/input/properties/bandstructure
basevect		/input/structure/crystal/basevect
bfieldc	@	/input/groundstate/spin/@bfieldc
box		./plot3d/box
chargedensityplot		/input/properties/chargedensityplot
coord	@	./origin/@coord
coord	@	./point/@coord
coord	@	/input/structure/species/atom/@coord
crystal		/input/structure/crystal
dos		/input/properties/dos
epsforce	@	/input/structureoptimization/@epsforce
epspot	@	/input/groundstate/@epspot
fermisurfaceplot		/input/properties/fermisurfaceplot
fixspin	@	/input/groundstate/spin/@fixspin
grid	@	./plot2d/parallelogram/@grid
grid	@	./plot3d/box/@grid
groundstate		/input/groundstate
href	@	/input/structure/species/@href
input		/input
kstlist		./kstlist
label	@	./point/@label
maxscl	@	/input/groundstate/@maxscl
mixer	@	/input/groundstate/@mixer
momfix	@	/input/groundstate/spin/@momfix
ngrdos	@	/input/properties/dos/@ngrdos
ngridk	@	/input/groundstate/@ngridk
nstfsp	@	/input/properties/fermisurfaceplot/@nstfsp
nwdos	@	/input/properties/dos/@nwdos
origin		./origin
parallelogram		./plot2d/parallelogram
path		./plot1d/path
plot1d		./plot1d
plot2d		./plot2d
plot3d		./plot3d
point		./point
pointstatepair		./pointstatepair
properties		/input/properties
reducek	@	/input/groundstate/@reducek
resume	@	/input/structureoptimization/@resume
rgkmax	@	/input/groundstate/@rgkmax
scale	@	/input/structure/crystal/@scale
separate	@	/input/properties/fermisurfaceplot/@separate
species		/input/structure/species
speciesfile	@	/input/structure/species/@speciesfile
speciespath	@	/input/structure/@speciespath
spin		/input/groundstate/spin
spinorb	@	/input/groundstate/spin/@spinorb
steps	@	./plot1d/path/@steps
stretch	@	/input/structure/crystal/@stretch
structure		/input/structure
structureoptimization		/input/structureoptimization
stype	@	/input/groundstate/@stype
swidth	@	/input/groundstate/@swidth
title		/input/title
xctype	@	/input/groundstate/@xctype

exciting

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Element: input

Element: title

Element: structure

Attribute: speciespath

Element: crystal

Attribute: scale

Attribute: stretch

Element: basevect

Element: species

Attribute: href

Attribute: speciesfile

Element: atom

Attribute: coord

Element: groundstate

Attribute: do

Attribute: epspot

Attribute: maxscl

Attribute: mixer

Attribute: ngridk

Attribute: reducek

Attribute: rgkmax

Attribute: stype

Attribute: swidth

Attribute: tforce

Attribute: xctype

Element: spin

Attribute: bfieldc

Attribute: fixspin

Attribute: momfix

Attribute: spinorb

Element: structureoptimization

Attribute: epsforce

Attribute: resume

Element: properties

Element: bandstructure

Attribute: scissor

Element: dos

Attribute: ngrdos

Attribute: nwdos

Attribute: scissor

Element: chargedensityplot

Element: fermisurfaceplot

Attribute: nstfsp

Attribute: separate

Element: origin

Attribute: coord

Element: point

Attribute: coord

Attribute: label

Element: plot1d

Element: path

Attribute: steps

Element: plot2d

Element: parallelogram

Attribute: grid

Element: plot3d

Element: box

Attribute: grid

Element: pointstatepair

Element: kstlist

Data Types

Type fortrandouble

Type vector

Type integerlist

Type vect3d

Type vect2d

Type integertriple

Type integerpair