Element: groundstate

The groundstate element is required for any calculation. Its attributes are the parameters and methods used to calculate the ground-state density.

This element allows for specification of the following attributes: ngridk (required), autokpt, beta0, betadec, betainc, cfdamp, chgexs, deband, dlinengyfermi, do, epsband, epschg, epsengy, epsforce, epsocc, epspot, fermilinengy, findlinentype, fracinr, frozencore, gmaxvr, isgkmax, ldapu, lmaxapw, lmaxinr, lmaxmat, lmaxvr, lradstep, maxscl, mixer, nempty, nktot, nosource, nosym, nprad, npsden, nwrite, ptnucl, radkpt, reducek, rgkmax, stype, swidth, symmorph, tetra, tevecsv, tfibs, tforce, vkloff, xctype

Attribute: autokpt

If "true", the set of k-points is determined automatically according to the total number of required k-points given by nktot.

Attribute: beta0

Initial value for mixing parameter. Used in linear mixing as choosen with mixer.

Attribute: betadec

Mixing parameter decrease. Used in linear mixing.

Attribute: betainc

Mixing parameter increase. Used in linear mixing.

Attribute: cfdamp

Damping coefficient for characteristic function.

Attribute: chgexs

This controls the amount of charge in the unit cell beyond that required to maintain neutrality. It can be set positive or negative depending on whether electron or hole doping is required.

Attribute: deband

Initial band energy step size The initial step length used when searching for the band energy, which is used as the APW linearisation energy. This is done by first searching upwards in energy until the radial wave-function at the muffin-tin radius is zero. This is the energy at the top of the band, denoted $E_{\rm t}$. A downward search is now performed from $E_{\rm t}$ until the slope of the radial wave-function at the muffin-tin radius is zero. This energy, $E_{\rm b}$, is at the bottom of the band. The band energy is taken as $(E_{\rm t}+E_{\rm b})/2$. If either $E_{\rm t}$ or $E_{\rm b}$ cannot be found then the band energy is set to the default value.

Attribute: dlinengyfermi

Energy difference between linearisation and Fermi energy.

Attribute: do

Decides if the ground state is calculated starting from scratch, using the densities from file or if it is skipped and only its associated input parameters are read in. Also applies fo structural optimization run.

Attribute: epsband

Energy tolerance for search of linearisation energies.

Attribute: epschg

Maximum allowed error in the calculated total charge beyond which a warning message will be issued.

Attribute: epsengy

Energy convergence tolerance.

Attribute: epsforce

Convergence tolerance for the forces during the SCF run.

Attribute: epsocc

smallest occupancy for which a state will contribute to the density.

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.

Attribute: fermilinengy

If "true" the linearization energies marked as non-varying are set to the Fermi level plus dlinengyfermi.

Attribute: findlinentype

Select method to determine the linearisation energies.

Attribute: fracinr

Fraction of the muffin-tin radius up to which lmaxinr is used as the angular momentum cut-off.

Attribute: frozencore

When set to "true" the frozen core approximation is applied, i.e., the core states are fixed to the atomic states.

Attribute: gmaxvr

Maximum length of |G| for expanding the interstitial density and potential.

Attribute: isgkmax

Species for which the muffin-tin radius will be used for calculating gkmax.

Attribute: ldapu

Type of LDA+U method to be used.

Attribute: lmaxapw

Angular momentum cut-off for the APW functions.

Attribute: lmaxinr

Close to the nucleus, the density and potential is almost spherical and therefore the spherical harmonic expansion can be truncated a low angular momentum. See also fracinr.

Attribute: lmaxmat

Angular momentum cut-off for the outer-most loop in the hamiltonian and overlap matrix setup.

Attribute: lmaxvr

Angular momentum cut-off for the muffin-tin density and potential.

Attribute: lradstep

Some muffin-tin functions (such as the density) are calculated on a coarse radial mesh and then interpolated onto a fine mesh. This is done for the sake of efficiency. lradstp defines the step size in going from the fine to the coarse radial mesh. If it is too large, loss of precision may occur.

Attribute: maxscl

Upper limit for te self-consistency loop.

Attribute: mixer

Select the mixing (relaxation) scheme for the SCF loop. One has the following options:

Linear mixer ("lin"):

Given the input $\mu^i$ and output $\nu^i$ vectors of the $i$th iteration, the next input vector to the ($i+1$)th iteration is generated using an adaptive mixing scheme. The $j$th component of the output vector is mixed with a fraction of the same component of the input vector:

where $\beta^i_j$ is set to $\beta_0$ at initialisation and increased by scaling with $\beta_{\rm inc}$ ($>1$) if $f^i_j\equiv\nu^i_j-\mu^i_j$ does not change sign between loops. If $f^i_j$ does change sign, then $\beta^i_j$ is scaled by $\beta_{\rm dec}$ ($>1$).

Multisecant Broyden potential mixing ("msec")

Pulay mixing ("pulay"):

Pulay's mixing scheme which uses direct inversion in the iterative subspace (DIIS). See Chem. Phys. Lett. 73, 393 (1980).

Attribute: nempty

Defines the number of eigenstates beyond that required for charge neutrality. When running metals it is not known a priori how many states will be below the Fermi energy for each k-point. Setting nempty greater than zero allows the additional states to act as a buffer in such cases. Furthermore, magnetic calculations use the first-variational eigenstates as a basis for setting up the second-variational Hamiltonian, and thus nempty will determine the size of this basis set. Convergence with respect to this quantity should be checked.

Attribute: ngridk

Number of k grid points along the basis vector directions.

Attribute: nktot

Used for the automatic determination of the ${\mathbf k}$-point mesh from the total number of k-points. If nktot is set, then the mesh will be determined in such a way that the number of k-points is proportional to the length of the reciprocal lattice vector in each direction and that the total number of k-points is less than or equal to nktot.

Attribute: nosource

When set to "true", source fields are projected out of the exchange-correlation magnetic field. experimental feature.

Attribute: nosym

When set to "true" no symmetries, apart from the identity, are used anywhere in the code.

Attribute: nprad

Order of predictor-corrector polynomial.

Attribute: npsden

oOrder of polynomial for pseudo-charge density.

Attribute: nwrite

Normally, the density and potentials are written to the file STATE.OUT only after com- pletion of the self-consistent loop. By setting nwrite to a positive integer the file will be written during the loop every nwrite iterations.

Attribute: ptnucl

The attrubute ptnucl is "true" if the nuclei are to be treated as point charges, if "false" the nuclei have a finite spherical distribution.

Attribute: radkpt

Used for the automatic determination of the k-point mesh. If autokpt is set to "true" then the mesh sizes will be determined by $n_i=\lambda/|{ \bf A}_i|+1$.

Attribute: reducek

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

Attribute: rgkmax

The parameter rgkmax implicitly determines the number of basis functions and is one of the crucial parameters for the accuracy of the calculation. It represents the product of two quantities: $R_{MT,\, Min}$, the smallest of all muffin-tin radii, and $|{ \bf G}+{ \bf k}|_{max}$, the maximum length for the ${ \bf G}+{ \bf k}$ vectors. Because each ${ \bf G}+{ \bf k}$ vector represents one basis function, rgkmax gives the number of basis functions used for solving the Kohn-Sham equations. Typical values of rgkmax are between 6 and 9. However, for systems with very short bond-lengths, significantly smaller values may be sufficient. This may especially be the case for materials containing carbon, where rgkmax may be 4.5-5, or hydrogen, where even values between 3 and 4 may be sufficient. In any case, a convergence check is indispensible for a proper choice of this parameter for your system!

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.

Attribute: swidth

Width of the smooth approximation to the Dirac delta function (must be greater than zero).

Attribute: symmorph

When set to "true" only symmorphic space-group operations are to be considered, i.e. only symmetries without non-primitive translations are used anywhere in the code.

Attribute: tetra

The attrubute "tetra" determines whether LIBBZINT library is used for k-/q-point generation and integration (experimental option).

Attribute: tevecsv

The attribute tevecsv is "true" if second-variational eigenvectors are calculated.

Attribute: tfibs

Because calculation of the incomplete basis set (IBS) correction to the force is fairly time- consuming, it can be switched off by setting tfibs to "false" This correction can then be included only when necessary, i.e. when the atoms are close to equilibrium in a structural relaxation run.

Attribute: tforce

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

Attribute: vkloff

The ${\mathbf k}$-point offset vector in lattice coordinates.

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)
• EXX, Exact Exchange, // Phys. Rev. Lett// 95, 136402 (2005)

If EXX is chosen, the element OEP has to be specified.

Element: spin

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

This element allows for specification of the following attributes: bfieldc, fixspin, momfix, reducebf, spinorb, spinsprl, taufsm, vqlss

Attribute: bfieldc

Allows 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

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 vectors in the atom elements. Collinear calculations are more efficient if the field is applied in the $z$-direction.

Attribute: fixspin

Attribute: momfix

The desired total moment for a FSM calculation.

Attribute: reducebf

After each iteration the external magnetic fields are multiplied with reducebf. This al- lows for a large external magnetic field at the start of the self-consistent loop to break spin symmetry, while at the end of the loop the field will be effectively zero, i.e. infinitesimal. See bfieldc and atom element.

Attribute: spinorb

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

Attribute: spinsprl

Set to "true" if a spin-spiral calculation is required. Experimental feature for the calculation of spin-spiral states. See vqlss for details.

Attribute: taufsm

Attribute: vqlss

Is the ${ \bf q}$-vector of the spin-spiral state in lattice coordinates. Spin-spirals arise from spinor states assumed to be of the form

These are determined using a second-variational approach, and give rise to a magnetization density of the form

where $m_x$, $m_y$ and $m_z$ are lattice periodic. See also spinsprl.

Element: solver

Optional configuration options for eigenvector solver.

This element allows for specification of the following attributes: epsarpack, evaltol, packedmatrixstorage, type

Attribute: epsarpack

Tolerance parameter for the ARPACK shift invert solver

Attribute: evaltol

Error tolerance for the first-variational eigenvalues using the LAPACK Solver

Attribute: packedmatrixstorage

In the default calculation the matrix is sored in packed form. When using multi-threaded BLAS setting this parameter to "false" increases efficiency.

Attribute: type

Selects the eigenvalue solver for the first variational equation

Element: OEP

Necessary, if exact exchange calculation is to be performed.

This element allows for specification of the following attributes: maxitoep, tauoep

Attribute: maxitoep

Maximum number of iterations when solving the exact exchange integral equations.

Attribute: tauoep

The optimised effective potential is determined using an iterative method. Phys. Rev. Lett// **98**, 196405 (2007). At the first iteration the step length is set to tauoep(1). During subsequent iterations, the step length is scaled by tauoep(2) or tauoep(3), when the residual is increasing or decreasing, respectively. See also maxitoep.

Element: output

Specifications on the file formats for output files.

This element allows for specification of the following attributes: state

Attribute: state

Selects the file format of the STATE file.

Element: libxc

This element allows for specification of the following attributes: correlation, exchange, xc

Attribute: correlation

Attribute: exchange

Attribute: xc

Combined functionals. If set it overrides the exchange and the correlation attributes. The hybrid functionals can be configured but are not supported. They may give nonsense results.

Reused Elements

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

Data Types

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