# Keywords¶

## Links to manual entries¶

**conductance:**

**dftb:**

## Summary of all keywords¶

`DispersionCorrection`

- Type
Multiple Choice

- Default value
None

- Options
[None, Auto, UFF, ULG, D2, D3-BJ, D4]

- GUI name
Dispersion

- Description
This key is used to specify an empirical dispersion model. Please refer to the DFTB documentation for details on the different methods. By default no dispersion correction will be applied. Setting this to auto applies the dispersion correction recommended in the DFTB parameter set’s metainfo file. Note that the D3-BJ dispersion correction is enabled by default when using the GFN1-xTB model Hamiltonian, but can be disabled manually by setting this keyword to None.

`KSpace`

- Type
Block

- Description
Options for the k-space integration (i.e. the grid used to sample the Brillouin zone).

`Quality`

- Type
Multiple Choice

- Default value
Normal

- Options
[GammaOnly, Basic, Normal, Good, VeryGood, Excellent]

- GUI name
K-space

- Description
Select the quality of the K-space grid used to sample the Brillouin Zone. If ‘GammaOnly’, only one point (the gamma point) will be used. For the other options, the actual number of K points generated depends on the size of the unit cell. The larger the real space cell, the fewer K points will be generated. The CPU-time and accuracy strongly depend on this option.

`Regular`

- Type
Block

- Description
Options for the regular k-space integration grid.

`NumberOfPoints`

- Type
Integer List

- Description
Use a regular grid with the specified number of k-points along each reciprocal lattice vector. For 1D periodic systems you should specify only one number, for 2D systems two numbers, and for 3D systems three numbers.

`Symmetric`

- Type
Block

- Description
Options for the symmetric k-space integration grid.

`KInteg`

- Type
Integer

- GUI name
Accuracy

- Description
Specify the accuracy for the Symmetric method. 1: absolutely minimal (only the G-point is used) 2: linear tetrahedron method, coarsest spacing 3: quadratic tetrahedron method, coarsest spacing 4,6,… (even): linear tetrahedron method 5,7…. (odd): quadratic method The tetrahedron method is usually by far inferior.

`Type`

- Type
Multiple Choice

- Default value
Regular

- Options
[Regular, Symmetric]

- GUI name
K-space grid type

- Description
The type of k-space integration grid used to sample the Brillouin zone (BZ) used. ‘Regular’: simple regular grid. ‘Symmetric’: symmetric grid for the irreducible wedge of the first BZ (useful when high-symmetry points in the BZ are needed to capture the correct physics of the system, graphene being a notable example).

`Model`

- Type
Multiple Choice

- Default value
GFN1-xTB

- Options
[DFTB, SCC-DFTB, DFTB3, GFN1-xTB, NonSCC-GFN1-xTB]

- Description
Selects the Hamiltonian used in the DFTB calculation: - DFTB/DFTB0/DFTB1 for classic DFTB without a self-consistent charge cycle - SCC-DFTB/DFTB2 with a self-consistency loop for the Mulliken charges - DFTB3 for additional third-order contributions. - GFN1-xTB for Grimme’s extended tight-binding model in the GFN1 version. - NonSCC-GFN1-xTB for a less accurate but faster version of GFN1-xTB without a self-consistency cycle The choice has to be supported by the selected parameter set.

`Occupation`

- Type
Block

- Description
Configures the details of how the molecular orbitals are occupied with electrons.

`KT`

- Type
Float

- Unit
Hartree

- Description
(KT) Boltmann constant times temperature, used for electronic temperature with strategy is auto. The default value is the default value for Temperature*3.166815423e-6. This key and Temperature are mutually exlusive.

`NumBoltz`

- Type
Integer

- Default value
10

- Description
The electronic temperature is done with a Riemann Stieltjes numerical integration, between zero and one occupation. This defines the number of points to be used.

`Strategy`

- Type
Multiple Choice

- Default value
Auto

- Options
[Auto, Aufbau, Fermi]

- GUI name
Occupation

- Description
This optional key allows to specify the fill strategy to use for the molecular orbitals. Can either be ‘Aufbau’ for simply filling the energetically lowest orbitals, or ‘Fermi’ for a smeared out Fermi-Dirac occupation. By default the occupation strategy is determined automatically, based on the other settings (such as the number of unpaired electrons).

`Temperature`

- Type
Float

- Default value
300.0

- Unit
Kelvin

- GUI name
Fermi temperature

- Description
The Fermi temperature used for the Fermi-Dirac distribution. Ignored in case of aufbau occupations.

`Periodic`

- Type
Block

- Description
Block that sets various details of the calculation only relevant for periodic systems.

`BZPath`

- Type
Block

- Description
If [BandStructure%Automatic] is disabled, DFTB will compute the band structure for the user-defined path in the [BZPath] block. You should define the vertices of your path in fractional coordinates (with respect to the reciprocal lattice vectors) in the [Path] sub-block. If you want to make a jump in your path, you need to specify a new [Path] sub-block.

`Path`

- Type
Non-standard block

- Recurring
True

- Description
A section of a k space path.

`BandStructure`

- Type
Block

- Description
Options for band structure plotting. This has no effect on the calculated energy. [Warning: The band structure is only computed in case of k-space sampling, i.e. it is not computed for Gamma-only calculations (see: Periodic%KSpace).]

`Automatic`

- Type
Bool

- Default value
Yes

- GUI name
Automatic generate path

- Description
Generate and use the standard path through the Brillouin zone. If not, use the user defined path (set via Custom path in the GUI, or with the Periodic%BZPath keyword in the run script).

`DeltaK`

- Type
Float

- Default value
0.1

- Unit
1/Bohr

- GUI name
Interpolation delta-K

- Description
Step size in reciprocal space for band structure interpolation. Using a smaller number will produce smoother band curves at an increased computational time.

`Enabled`

- Type
Bool

- Default value
Yes

- GUI name
Calculate band structure

- Description
Whether or not to calculate the band structure.

`FatBands`

- Type
Bool

- Default value
Yes

- GUI name
Calculate fatbands

- Description
Control the computation of the fat bands (only when the bandstructure is calculated). The fat bands are the periodic equivalent of the Mulliken population analysis. The definition of the fat bands can be found in the Band Documentation.

`UseSymmetry`

- Type
Bool

- Default value
Yes

- Description
If set, only the irreducible wedge of the Wigner-Seitz cell is sampled. If not, the whole (inversion-unique) Wigner-Seitz cell is sampled.

`DOS`

- Type
Block

- Description
The subkeys of [DOS] allow to customize the calculation of the density of states.

`EMax`

- Type
Float

- Default value
0.75

- Unit
Hartree

- Description
Upper end of the energy interval in which the density of states is calculated.

`EMin`

- Type
Float

- Default value
-0.75

- Unit
Hartree

- Description
Lower end of the energy interval in which the density of states is calculated.

`Enabled`

- Type
Bool

- Default value
Yes

- GUI name
Calculate DOS

- Description
Whether or not to calculate the DOS. Note that the DOS will always be calculated when also the band structure is calculated.

`NSteps`

- Type
Integer

- Default value
300

- Description
The number of energy intervals between [EMin] and [EMax] for which the density of states is calculated.

`EffectiveMass`

- Type
Block

- Description
In a semi-conductor, the mobility of electrons and holes is related to the curvature of the bands at the top of the valence band and the bottom of the conduction band. With the effective mass option, this curvature is obtained by numerical differentiation. The estimation is done with the specified step size, and twice the specified step size, and both results are printed to give a hint on the accuracy. By far the most convenient way to use this key is without specifying any options.

`Enabled`

- Type
Bool

- Default value
No

- GUI name
Effective mass

- Description
In a semi-conductor, the mobility of electrons and holes is related to the curvature of the bands at the top of the valence band and the bottom of the conduction band. With the effective mass option, this curvature is obtained by numerical differentiation. The estimation is done with the specified step size, and twice the specified step size, and both results are printed to give a hint on the accuracy. By far the most convenient way to use this key is without specifying any options.

`KPointCoord`

- Type
Float List

- Unit
1/Bohr

- Recurring
True

- GUI name
At K-point

- Description
Coordinate of the k-points for which you would like to compute the effective mass.

`NumAbove`

- Type
Integer

- Default value
1

- GUI name
Include N bands above

- Description
Number of bands to take into account above the Fermi level.

`NumBelow`

- Type
Integer

- Default value
1

- GUI name
Include N bands below

- Description
Number of bands to take into account below the Fermi level.

`StepSize`

- Type
Float

- Default value
0.001

- Description
Size of the step taken in reciprocal space to perform the numerical differentiation

`Properties`

- Type
Block

- Description
DFTB can calculate various properties of the simulated system. This block configures which properties will be calculated.

`Excitations`

- Type
Block

- Description
Contains all options related to the calculation of excited states, either as simple single orbitals transitions or from a TD-DFTB calculation.

`SingleOrbTrans`

- Type
Block

- Description
The simplest approximation to the true excitations are the single orbital transitions (sometimes called Kohn-Sham transitions), that is transitions where a single electron is excited from an occupied Kohn-Sham orbital into a virtual orbital. The calculation of these transitions is configured in this section. Note that the SingleOrbTrans section is optional even though the single orbital transitions are also needed for TD-DFTB calculations. If the section is not present all single orbital transitions will still be calculated and used in a subsequent TD-DFTB calculation, but no output will be produced.

`Enabled`

- Type
Bool

- Default value
No

- GUI name
Single orbital transisitions: Calculate

- Description
Calculate the single orbital transitions.

`Filter`

- Type
Block

- Description
This section allows to remove single orbital transitions based on certain criteria. All filters are disabled by default.

`OSMin`

- Type
Float

- GUI name
Minimum oscillator strength

- Description
Removes single orbital transitions with an oscillator strength smaller than this threshold. A typical value to start (if used at all) would be 1.0e-3.

`dEMax`

- Type
Float

- Unit
Hartree

- Description
Removes single orbital transitions with an orbital energy difference larger than this threshold.

`dEMin`

- Type
Float

- Unit
Hartree

- Description
Removes single orbital transitions with an orbital energy difference smaller than this threshold.

`PrintLowest`

- Type
Integer

- Default value
10

- Description
The number of single orbital transitions that are printed to the screen and written to disk. If not a TD-DFTB calculation, the default is to print the 10 lowest single orbital transitions. In case of a TD-DFTB calculation it is assumed that the single orbital transitions are only used as an input for TD-DFTB and nothing will be printed unless PrintLowest is specified explicitly.

`TDDFTB`

- Type
Block

- Description
Calculations with time-dependent DFTB can be configured in the TDDFTB section and should in general give better results than the raw single orbital transitions. TD-DFTB calculates the excitations in the basis of the single orbital transitions, whose calculation is configured in the SingleOrbTrans section. Using a filter in SingleOrbTrans can therefore be used to reduce the size of the basis for TD-DFTB. One possible application of this is to accelerate the calculation of electronic absorption spectra by removing single orbital transitions with small oscillator strengths from the basis. Note that the entire TDDFTB section is optional. If no TDDFTB section is found, the behavior depends on the existence of the SingleOrbTrans section: If no SingleOrbTrans section is found (the Excitations section is completely empty then) a TD-DFTB calculation with default parameters will be performed. If only the SingleOrbTrans section is present no TD-DFTB calculation will be done.

`Calc`

- Type
Multiple Choice

- Default value
None

- Options
[None, Singlet, Triplet]

- GUI name
Type of excitations

- Description
Specifies the multiplicity of the excitations to be calculated.

`DavidsonConfig`

- Type
Block

- Description
This section contains a number of keywords that can be used to override various internals of the Davidson eigensolver. The default values should generally be fine.

`ATCharges`

- Type
Multiple Choice

- Default value
Precalc

- Options
[Precalc, OnTheFly]

- GUI name
Transition charges

- Description
Select whether the atomic transition charges are precalculated in advance or reevaluated during the iterations of the Davidson solver. Precalculating the charges will improve the performance, but requires additional storage. The default is to precalculate the atomic transition charges, but the precalculation may be disabled if not not enough memory is available.

`SafetyMargin`

- Type
Integer

- Default value
4

- Description
The number of eigenvectors the Davidson method will calculate in addition to the ones requested by the user. With the Davidson eigensolver it is generally a good idea to calculate a few more eigenvectors than needed, as depending on the initial guess for the eigenvectors it can happen that the found ones are not exactly the lowest ones. This problem is especially prominent if one wants to calculate only a small number of excitations for a symmetric molecule, where the initial guesses for the eigenvectors might have the wrong symmetry. Note that the additionally calculated excitations will neither be written to the result file nor be visible in the output.

`Tolerance`

- Type
Float

- Default value
1e-09

- Description
Convergence criterion for the norm of the residual.

`Diagonalization`

- Type
Multiple Choice

- Default value
Auto

- Options
[Auto, Davidson, Exact]

- GUI name
Method

- Description
Select the method used to solve the TD-DFTB eigenvalue equation. The most straightforward procedure is a direct diagonalization of the matrix from which the excitation energies and oscillator strengths are obtained. Since the matrix grows quickly with system size (number of used single orbital transitions squared), this option is possible only for small molecules. The alternative is the iterative Davidson method, which finds a few of the lowest excitations within an error tolerance without ever storing the full matrix. The default is to make this decision automatically based on the system size and the requested number of excitations.

`Lowest`

- Type
Integer

- Default value
10

- GUI name
Number of excitations

- Description
Specifies the number of excitations that are calculated. Note that in case of the exact diagonalization all excitations are calculated, but only the lowest ones are printed to screen and written to the output file. Also note that if limited both by number and by energy, (lowest and upto), DFTB will always use whatever results in the smaller number of calculated excitations.

`Print`

- Type
String

- Description
Specifies whether to print details on the contribution of the individual single orbital transitions to the calculated excitations.

`ScaleKernel`

- Type
Float

- Default value
1.0

- Unit
None

- Description
Set the scaling parameter of the response kernel. A scaling approach can be used to identify plasmons in molecules. While single-particle excitations are only slightly affected by scaling of the response kernel, plasmonic excitations are sensitive to variations in the scaling parameter. Default no scaling is used (scaling parameter = 1.0)

`UpTo`

- Type
Float

- Unit
Hartree

- GUI name
Excitations up to

- Description
Set the maximum excitation energy. Attempts to calculate all excitations up to a given energy by calculating a number of excitations equal to the number of single orbital transitions in this window. This is only approximately correct, so one should always add some safety margin. Note that if limited both by number and by energy, (lowest and upto), DFTB will always use whatever results in the smaller number of calculated excitations.

`TDDFTBGradients`

- Type
Block

- Description
This block configures the calculation of analytical gradients for the TD-DFTB excitation energies, which allows the optimization of excited state geometries and the calculation of vibrational frequencies in excited states (see J. Comput. Chem., 28: 2589-2601). If the gradients are calculated, they will automatically be used for geometry optimizations or vibrational frequency calculations, if the corresponding Task is selected and only 1 excitation is selected. Vibrationally resolved UV/Vis spectroscopy (Franck-Condon Factors) can be calculated in combination with the FCF program or using the Vibrational Analysis Tools in AMS. See the ADF documentation on Vibrationally resolved electronic spectra or the AMS documentation for the Vibrational Analysis Tools.

`Eigenfollow`

- Type
Bool

- Default value
No

- GUI name
Follow initial excitation

- Description
If this option is set, DFTB uses the transition density in atomic orbital basis to follow the initially selected excited state during a geometry optimization. This is useful if excited state potential energy surfaces cross each other and you want to follow the surface you started on.

`Excitation`

- Type
Integer List

- GUI name
Excitation number

- Description
Select which excited states to calculate the gradients for. Gradients can only be calculated for an excited states that has been calculated using TD-DFTB. Make sure that enough excitations are calculated.

`Fragments`

- Type
Block

- Description
Fragment files

`Analysis`

- Type
Bool

- Default value
Yes

- GUI name
Fragment analysis

- Description
Mulliken population analysis in terms of fragment orbitals.

`EMax`

- Type
Float

- Default value
0.25

- Unit
Hartree

- Description
Upper end of the energy interval for which the orbitals are analyzed.

`Emin`

- Type
Float

- Default value
-0.75

- Unit
Hartree

- Description
Lower end of the energy interval for which the orbitals are analyzed.

`File`

- Type
String

- Recurring
True

- Description
Path (either absolute or relative) of fragment file

`TIDegeneracyThreshold`

- Type
Float

- Default value
0.1

- Unit
eV

- Description
If the orbital energy of the fragment MO is within this threshold with fragment HOMO or LUMO energy, then this fragment MO is included in the calculation of the transfer integrals. Relevant in case there is (near) degeneracy.

`TransferIntegrals`

- Type
Bool

- Default value
No

- GUI name
Charge transfer integrals

- Description
Calculate the charge transfer integrals, spatial overlap integrals and site energies. Charge transfer integrals can be used in models that calculate transport properties.

`NBOInput`

- Type
Bool

- Default value
No

- Description
Whether or not an input file for the NBO program is written to disk as nboInput.FILE47. The input file follows the FILE47 format as described in the NBO6 manual available on nbo6.chem.wisc.edu. By default, only the calculation of the natural bond orbitals and the natural localized molecular orbitals is enabled, but the nboInput.FILE47 file can be edited by hand to enable other analysis models. Please refer to the NBO6 manual for details.

`RESPONSE`

- Type
Block

- Description
Linear response module to compute electric (complex) polarizabilities

`Frequencies`

- Type
Float List

- Default value
[0.0]

- Unit
eV

- Description
List of frequencies of incident light

`LifeTime`

- Type
Float

- Unit
Hartree

- Description
Phenomenological damping

`Solver`

- Type
Block

- Description
Solver details for CPKS

`Algorithm`

- Type
Multiple Choice

- Default value
EXACT

- Options
[EXACT, ITER]

- Description
Choice of solver for CPKS

`Debug`

- Type
Bool

- Default value
No

- Description
Print technical information from solver

`NumIt`

- Type
Integer

- Default value
100

- Description
Maximum number of iterations (ITER solver only)

`RMSE`

- Type
Float

- Default value
1e-06

- Description
Threshold for convergence (ITER solver only)

`QMFQ`

- Type
Block

- Description
Block input key for QM/FQ(FMu).

`AtomType`

- Type
Block

- Recurring
True

- Description
Definition of atomic types in MM environment

`Alpha`

- Type
Float

- Description
Polarizability of FQFMU atom

`Charge`

- Type
Float

- Description
MM fixed charge (non-polarizable only)

`Chi`

- Type
Float

- Description
Electronegativity of FQ atom

`Eta`

- Type
Float

- Description
Chemical Hardness of FQ atom

`Symbol`

- Type
String

- Description
Symbol associated with atom type

`Coords`

- Type
Non-standard block

- Description
Coordinates and fragment information (FQ only)

`Forcefield`

- Type
Multiple Choice

- Default value
FQ

- Options
[FQ, FQFMU, NOPOL]

- Description
Version of the FQ family of polarizable forcefields

`Frozen`

- Type
Bool

- Default value
No

- Description
Expert option. Do not introduce polarization effect in response calculations.

`Kernel`

- Type
Multiple Choice

- Default value
OHNO

- Options
[OHNO, COUL, GAUS]

- Description
Expert option. KERNEL can be used to choose the functional form of the charge-charge interaction kernel between MM atoms. Recommended is to use the default OHNO. The COUL screening is the standard Coulomb interaction 1/r. The OHNO choice introduce the Ohno functional (see [K. Ohno, Theoret. Chim. Acta 2, 219 (1964)]), which depends on a parameter n that is set equal to 2. Finally, the GAUS screening models each FQ charge by means of a spherical Gaussian-type distribution, and the interaction kernel is obtained accordingly. For QM/FQFMU only GAUS SCREEN is implemented.

`MolCharge`

- Type
Float

- Default value
0.0

- Description
Total charge of each fragment (FQ only)

`Repulsion`

- Type
Block

- Description
Configures various details of the repulsive potential.

`ResourcesDir`

- Type
String

- Description
The directory containing the parameter files. The path can be absolute or relative. Relative paths starting with ./ are considered relative to the directory in which the calculation is started, otherwise they are considered relative to $AMSRESOURCES/DFTB. This key is required for the Slater-Koster based DFTB models, but optional for xTB.

`SCC`

- Type
Block

- Description
This optional section configures various details of the self-consistent charge cycle. If the model Hamiltonian does not need a self-consistent solution (e.g. plain DFTB0), none of this information is used and the entire section will be ignored.

`AdaptiveMixing`

- Type
Bool

- Default value
Yes

- Description
Change the mixing parameter based on the monitored energy. A significant increase of energy will strongly reduce the mixing. Then it will slowly grow back to the SCC%Mixing value.

`AlwaysClaimConvergence`

- Type
Bool

- Default value
No

- Description
Even if the SCC does not converge, claim convergence.

`Converge`

- Type
Block

- Description
Controls the convergence criteria of the SCC cycle.

`Charge`

- Type
Float

- Default value
1e-08

- GUI name
Charge convergence

- Description
The maximum change in atomic charges between subsequent SCC iterations. If the charges change less, the SCC cycle is considered converged.

`Norm`

- Type
Multiple Choice

- Default value
L-Infinity

- Options
[L2, L-Infinity]

- Description
The LInfinity norm is the more stringent choice. The L2 norm is directly what is optimized by the DIIS procedure, it is scaled by the extra constant factor 2/sqrt(nAtoms).

`DIIS`

- Type
Block

- Description
Parameters influencing the DIIS self-consistency method

`Enabled`

- Type
Bool

- Default value
Yes

- Description
If not enabled simple mixing without DIIS acceleration will be used.

`MaxSamples`

- Type
Integer

- Default value
20

- Description
Specifies the maximum number of samples considered during the direct inversion of iteration of subspace (DIIS) extrapolation of the atomic charges during the SCC iterations. A smaller number of samples potentially leads to a more aggressive convergence acceleration, while a larger number often guarantees a more stable iteration. Due to often occurring linear dependencies within the set of sample vectors, the maximum number of samples is reached only in very rare cases.

`MaximumCoefficient`

- Type
Float

- Default value
10.0

- Description
When the diis expansion coefficients exceed this threshold, the solution is rejected. The vector space is too crowded. The oldest vector is discarded, and the expansion is re-evaluated.

`MinSamples`

- Type
Integer

- Default value
-1

- Description
When bigger than one, this affects the shrinking of the DIIS space on linear depence. It will not reduce to a smaller space than MinSamples unless there is extreme dependency.

`MixingFactor`

- Type
Float

- Default value
0.15

- Description
The parameter used to mix the DIIS linear combination of previously sampled atomic charge vectors with an analogous linear combination of charge vectors resulting from population analysis combination. It can assume real values between 0 and 1.

`HXDamping`

- Type
Bool

- Description
This option activates the DFTB3 style damping for H-X bonds. Note that this is always enabled if the DFTB%Model key is set to DFTB3. Not used with xTB.

`InheritMixFromPreviousResult`

- Type
Bool

- Default value
No

- Description
For some run types, such as GeometryOptimization, a previous result is available. By using the charges from the previous geometry a better initial guess for the SCC procedure may be obtained. Also the last mix factor from the previous result can be loaded, possibly speeding up the SCC.

`Iterations`

- Type
Integer

- Default value
500

- Description
Allows to specify the maximum number of SCC iterations. The default should suffice for most standard calculations. Convergence issues may arise due to the use of the Aufbau occupations for systems with small HOMO-LUMO gaps. In this case the use of a Fermi broadening strategy may improve convergence. Choosing a smaller mixing parameter (see DFTB%SCC%Mixing) may also help with convergence issues: it often provides a more stable but slower way to converge the SCC cycle.

`Method`

- Type
Multiple Choice

- Default value
MultiStepper

- Options
[DIIS, MultiStepper]

- Description
The DIIS option is the old method. The MultiStepper is much more flexible and is controlled by the SCFMultiSolver block

`MinimumAdaptiveMixingFactor`

- Type
Float

- Default value
0.003

- Description
In case of AdaptiveMixing the lower bound for the MixingFactor.

`MultiStepperPresetPath`

- Type
String

- Default value
DFTB/default2023.inc

- Description
Name of file containing a SCFMultiStepper key block. This will be used if no Explicit SCFMultiStepper block is in the input, and Method=MultiStepper. If the path is not absolute, it is relative to $AMSHOME/data/presets/multi_stepper’

`OrbitalDependent`

- Type
Bool

- Description
Activates or disables orbital resolved calculations. If this key is absent the recommended settings from the parameter file’s metainfo.

`SCFMultiStepper`

- Type
Block

- Description
To solve the self-consistent problem multiple steppers can be tried during stints using the ones that give the best progress.

`AlwaysChangeStepper`

- Type
Bool

- Default value
No

- Description
When the progress is fine there is no reason to change the stepper. In practice this is always set to true, because also the Stepper%ExpectedSlope can be used to achieve similar behavior.

`ErrorGrowthAbortFactor`

- Type
Float

- Default value
1000.0

- Description
Abort stint when the error grows too much, compared to the error at the start of the stint.

`FractionalStepFactor`

- Type
Float

- Default value
-1.0

- Description
Multiply the step by this factor. If smaller than zero this is not used.

`MinStintCyclesForAbort`

- Type
Integer

- Default value
0

- Description
Look at ErrorGrowthAbortFactor only when a number of steps has been completed since the start of the stint. A value of 0 means always.

`Stepper`

- Type
Block

- Recurring
True

- Description
??

`AbortSlope`

- Type
Float

- Default value
100.0

- Description
If the slope (at the end of a stint) is larger than this: abort the stepper

`DIISStepper`

- Type
Block

- Description
DIIS stepper

`EDIISAlpha`

- Type
Float

- Default value
0.01

- Description
The extra energy vector is weighed by this factor. .

`MaxCoefficient`

- Type
Float

- Default value
20.0

- Description
The largest allowed value of the expansion coefficients. If exceed the number of vectors is reduces until the criterion is met.

`MaxVectors`

- Type
Integer

- Default value
10

- Description
Maximum number of previous densities to be used (size of the history).

`MinVectors`

- Type
Integer

- Default value
-1

- Description
Try to prevent to make nVectors shrink below this value, by allowing for significantly larger coefficents.

`Mix`

- Type
Float

- Default value
0.2

- Description
Also known as greed. It determines the amount of output density to be used. May be changed by the MixAdapter.

`ErrorGrowthAbortFactor`

- Type
Float

- Default value
-1.0

- Description
Abort stint when the error grows too much, compared to the error at the start of the stint. Overides global ErrorGrowthAbortFactor when set to a value > 0

`ExpectedSlope`

- Type
Float

- Default value
-100.0

- Description
If the slope of the total SCF is better than this keep on going.

`FractionalStepFactor`

- Type
Float

- Default value
-1.0

- Description
Multiply the step by this factor. If smaller than zero this is not used.

`MaxInitialError`

- Type
Float

- Description
Only use the stepper when error is smaller than this.

`MaxIterationNumber`

- Type
Integer

- Default value
-1

- Description
Stepper will only be active for iterations smaller than this number. (Negative value means: Ignore this option)

`MaxStintNumber`

- Type
Integer

- Default value
-1

- Description
Stepper will only be active for stints smaller than this number. (Negative value means: Ignore this option)

`MinInitialError`

- Type
Float

- Description
Only use the stepper when error is larger than this.

`MinIterationNumber`

- Type
Integer

- Default value
-1

- Description
Stepper will only be active for iterations larger than this number.

`MinStintCyclesForAbort`

- Type
Integer

- Default value
0

- Description
Look at ErrorGrowthAbortFactor only when a number of steps has been completed since the start of the stint. A value of 0 means always. Overides global value.

`MinStintNumber`

- Type
Integer

- Default value
-1

- Description
Stepper will only be active for stints larger than this number.

`MixAdapter`

- Type
Block

- Description
Generic mix adapter

`ErrorGrowthPanicFactor`

- Type
Float

- Default value
10.0

- Description
When the error increases more than this factor, this mix is reduced a lot.

`GrowthFactor`

- Type
Float

- Default value
1.1

- Description
When the mix is considered too low it is multiplied by this factor. Otherwise it is divided by it.

`MaxMix`

- Type
Float

- Default value
0.3

- Description
Do not grow the mix above this value.

`MinMix`

- Type
Float

- Default value
0.1

- Description
Do not shrink the mix below this value.

`NTrialMixFactors`

- Type
Integer

- Default value
3

- Description
Only used with Type=Trial. Must be an odd number.

`TrialMode`

- Type
Multiple Choice

- Default value
CurrentMixCentered

- Options
[CurrentMixCentered, FullRange]

- Description
How are the NTrialMixFactors chosen?

`Type`

- Type
Multiple Choice

- Default value
Error

- Options
[Error, Energy, UnpredictedStep, Trial]

- Description
Adapt the mix factor based on the observed progress (slope).

`MixStepper`

- Type
Block

- Description
Simple mixing stepper, only using the previous (in/out) denstity.

`Mix`

- Type
Float

- Default value
0.1

- Description
???.

`MultiSecantStepper`

- Type
Block

- Description
Multi secant stepper.

`MaxCoefficient`

- Type
Float

- Default value
20.0

- Description
???.

`MaxVectors`

- Type
Integer

- Default value
10

- Description
???.

`Mix`

- Type
Float

- Default value
0.2

- Description
???.

`Variant`

- Type
Multiple Choice

- Default value
MSB2

- Options
[MSB1, MSB2, MSR1, MSR1s]

- Description
There are several version of the Multi secant method.

`StintLength`

- Type
Integer

- Description
Override global StintLength.

`StintLength`

- Type
Integer

- Default value
10

- Description
A stepper is active during a number of SCF cycles, called a stint.

`UsePreviousStintForErrorGrowthAbort`

- Type
Bool

- Default value
No

- Description
The error is normally checked against the first error of the stint. With this option that will be the one from the previous stint, if performed with the same stepper.

`Unrestricted`

- Type
Bool

- Default value
No

- Description
Enables spin unrestricted calculations. Only collinear spin polarization is supported, see Theor Chem Acc (2016) 135: 232, for details. Must be supported by the chosen parameter set. Not yet compatible with DFTB3, k-space sampling periodic calculations or the xTB models.

`Solvation`

- Type
Block

- Description
Generalized Born solvation model with Solvent Accessible Surface Area (GBSA).

`GSolvState`

- Type
Multiple Choice

- Default value
Gas1MSolvent1M

- Options
[Gas1BarSolvent, Gas1MSolvent1M, Gas1BarSolvent1M]

- Description
Reference state for solvation free energy shift.

`Solvent`

- Type
Multiple Choice

- Default value
None

- Options
[None, Acetone, Acetonitrile, CHCl3, CS2, DMSO, Ether, H2O, Methanol, THF, Toluene]

- Description
Solvent used in the GBSA implicit solvation model.

`SurfaceGrid`

- Type
Multiple Choice

- Default value
230

- Options
[230, 974, 2030, 5810]

- Description
Number of angular grid points for the construction of the solvent accessible surface area. Usually the default number of grid point suffices, but in case of suspicious behaviors you can increase the number of points.

`Temperature`

- Type
Float

- Default value
298.15

- Unit
Kelvin

- Description
The temperature used when calculating the solvation free energy shift. Only used for ‘Gas1BarSolvent’ and ‘Gas1BarSolvent1M’ GSolvState options.

`UseGSASA`

- Type
Bool

- Default value
Yes

- GUI name
Solvation Free Energy

- Description
Include shift term and G(SASA) terms in the energy and gradient.

`StoreMatrices`

- Type
Bool

- Default value
No

- Description
Determines whether the Hamiltonian and overlap matrices are stored in the binary result file.

`StoreOrbitals`

- Type
Bool

- Default value
Yes

- Description
Determines whether the orbitial coefficients are stored in the binary result file. They are needed for displaying orbitals and densities in amsview.

`Technical`

- Type
Block

- Description
This optional section is about technical aspects of the program that should not concern the normal user.

`AnalyticalStressTensor`

- Type
Bool

- Default value
Yes

- Description
Whether to compute the stress tensor analytically. Note: This can only be used together with Ewald summation as it will give (slightly) wrong results with Madelung screening.

`EwaldSummation`

- Type
Block

- Description
Configures the details of the Ewald summation of the Coulomb interaction.

`CellRangeFactor`

- Type
Float

- Default value
2.0

- Description
Smaller values will make the Ewald summation less accurate but faster.

`Enabled`

- Type
Bool

- Default value
Yes

- Description
Whether to use Ewald summation for the long-range part of the Coulomb interaction. Otherwise screening is used.

`Tolerance`

- Type
Float

- Default value
1e-10

- Description
Larger values will make the Ewald summation less accurate but faster.

`MatricesViaFullMaxSize`

- Type
Integer

- Default value
2047

- Description
Matrices smaller than this size are constructed via a full matrix. This is faster, but uses more memory in the construction.

`Parallel`

- Type
Block

- Description
Calculation of the orbitals in several k-points is trivially parallel.

`nCoresPerGroup`

- Type
Integer

- Description
Number of cores in each working group.

`nGroups`

- Type
Integer

- Description
Total number of processor groups. This is the number of tasks that will be executed in parallel.

`nNodesPerGroup`

- Type
Integer

- GUI name
Cores per task

- Description
Number of nodes in each group. This option should only be used on homogeneous compute clusters, where all used compute nodes have the same number of processor cores.

`ReuseKSpaceConfig`

- Type
Bool

- Default value
Yes

- Description
Keep the number of k-points constant during a lattice optimization. Otherwise the PES might display jumps, because the number of points depends on the lattice vector sizes. If this option is on it will always use the number of k-points that was used from a previous result.

`Screening`

- Type
Block

- Description
For SCC-DFTB in periodic systems the Coulomb interaction can (instead of using Ewald summation) be screened with a Fermi-Dirac like function defined as S(r)=1/(exp((r-r_madel)/d_madel)+1). This section allows to change some details of the screening procedure. Note that Coulomb screening is only used if the Ewald summation is disabled.

`dMadel`

- Type
Float

- Unit
Bohr

- Description
Sets the smoothness of the screening function. The default is 1/10 of [rMadel].

`rMadel`

- Type
Float

- Unit
Bohr

- Description
Sets the range of the screening function. The default is 2x the norm of the longest lattice vector.

`UseGeneralizedDiagonalization`

- Type
Bool

- Default value
Yes

- Description
Whether or not to use generalized diagonalization. Does not affect the results, but might be faster or slower.

`UnpairedElectrons`

- Type
Integer

- Default value
0

- GUI name
Spin polarization

- Description
This specifies the number of unpaired electrons (not the multiplicity!). This number will then be used in the orbital-filling strategy. Has to be compatible with the total number of electrons, meaning it must be an even number if the total number of electrons is even and odd if the total number is odd. Must be an integer value. Note that this does not activate spin polarization, it only affects the filling of the orbitals.

`XTBConfig`

- Type
Block

- Description
This block allows for minor tweaking.

`SlaterRadialThreshold`

- Type
Float

- Default value
1e-05

- Description
Threshold determining the range of the basis functions. Using a larger threshold will speed up the calculation, but will also make the results less accurate.

`useXBTerm`

- Type
Bool

- Default value
No

- Description
Whether to use the Halogen bonding (XB) term. This is not advised as it has a non-continuous PES.