Keywords¶

Engine DFTB¶

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:

Auto

Options:

[Auto, 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 ‘Auto’, the quality defined in the ‘NumericalQuality’ will be used. If ‘GammaOnly’, only one point (the gamma point) will be used.

The actual number of K points generated depends on this option and 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) Boltzmann 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 exclusive.

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.

UseSeeKPath

Type:

Bool

Default value:

No

Description:

This option determines how the path through the Brillouin zone is generated when Automatic mode is enabled. Choosing Yes utilizes the external utility **SeeKPath** to automatically generate the k-path, leveraging its robust algorithm for finding an appropriate path through the high-symmetry points. Choosing No uses our built-in **KPath** program to generate the k-path. Please note that using **SeeKPath** for k-path generation is currently an experimental feature. See https://github.com/giovannipizzi/seekpath and https://doi.org/10.1016/j.commatsci.2016.10.015 for details about SeeKPath.

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 dependence. 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 coefficients.

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. Overrides 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. Overrides 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) density.

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.

SpinOrbit

Type:

Bool

Default value:

No

Description:

test

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 orbital 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.

conductance¶

EnergyGrid

Type:

Block

Description:

Energy grid for Transmission Function

Max

Type:

Float

Default value:

5.0

Unit:

eV

Description:

Max Energy (relative to Fermi energy)

Min

Type:

Float

Default value:

-5.0

Unit:

eV

Description:

Min energy (relative to Fermi energy)

Num

Type:

Integer

Default value:

200

Description:

Number of energy values in which the interval Min-Max is subdivided

Files

Type:

Block

Description:

path of files

HamiltonianElectrode

Type:

String

Default value:

Description:

HamiltonianMolecule

Type:

String

Default value:

Description:

Leads

Type:

String

Default value:

Description:

Path (either absolute or relative) of the lead results file

OverlapElectrode

Type:

String

Default value:

Description:

OverlapMolecule

Type:

String

Default value:

Description:

Scattering

Type:

String

Default value:

Description:

Path (either absolute or relative) of the scattering region results

Output

Type:

Block

Description:

options describing what should be printed

OldOutput

Type:

Bool

Default value:

No

Description:

Physics

Type:

Block

Description:

Block describing the physics of the system

FermiEnergy

Type:

Block

Description:

Block describing the physics of the system

Electrode

Type:

Float

Default value:

0.0

Description:

Fermi energy of the electrode

Technical

Type:

Block

Description:

options describing technical parts of the calculation

Eta

Type:

Float

Default value:

1e-05

Description:

To avoid poles of the Green’s function, a small imaginary number is added to the energy

overwriteLeads

Type:

Bool

Default value:

Yes

Description:

If true, Hamiltonians H_L and H_R are taken from the DFTB-leads calculation. If False, they are taken from the DFTB scattering-region calculation

setOffDiagonalToZero

Type:

Bool

Default value:

Yes

Description:

If true, H_LR and S_LR are explicitly set to zero. If False, they are taken from the DFTB scattering-region calculation.