SimulationParameter{ }

Calling sequence

SimulationParameter{ }

Dependencies
Functionality

Specifies parameters related to physical assumptions and numerics. Please refer to Coherence length, Electronic band structure, Axial energy cut-off, Green’s functions and Convergence for the model description.

Example
SimulationParameter{
    # coherence length
    CoherenceLengthInPeriods = 1
    CoherenceLengthInNm =
    CoherenceLengthSelfEnergy =

    # basis state calculation
    SpatialGridSpacing = 0.3
    nLateralPeriodsForBandStructure = 1
    SmoothingLengthKP = 0.1
    ContinuousValenceBand = no

    AssumeIntrinsicNeutrality = no

    # axial energy cut-off by energy value
    EnergyRangeAxial = 60
    EnergyRangeAxialValence = 50

    # axial energy cut-off by number of subbands
    NumberOfConductionSubbands = 1
    NumberOfValenceSubbands = 2

    # lateral energy cut-off
    EnergyRangeLateral = 200

    # energy range of Green's functions
    EnergyGridSpacing = 5
    EminShift = 0
    EmaxShift = 0

    # convergence
    ConvergenceValueGF =
    ConvergenceValueCurrent =
    ConvergenceMinimum =
    NMaxIterations = 500
    ConvergFactInit =
    ConvergFactMin =
    ConvergFactMax =
    ExitLoopIfNoConvergAfter =
    PhononConvergence =

    StartFromEquilibrium = yes
}

CoherenceLengthInPeriods

Calling sequence

SimulationParameter{ CoherenceLengthInPeriods }

Properties

  • type: \(\mathrm{integer}\)

  • values: {0, 1, 2, 3, ...}

Functionality

Sets the accounted coherence length of electrons in numbers of period. 1 should be enough for almost all existing QCL designs. In contrast, a larger number is needed for superlattices. See Coherence length for the model description.

Note

The gain spectra should be independent of the number of periods since the material gain is averaged over one period.

CoherenceLengthInNm

Calling sequence

SimulationParameter{ CoherenceLengthInNm }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{nm}\)

Functionality

Further limits the coherence length [nm] for which self-energies are considered. This will speed up the calculation of the self-energies. On the other hand, this can reduce the accuracy of the scattering processes if this length is below the actual coherence length in the simulated device. It is recommended to assess the accuracy of such approximation by comparing to the results from different coherence lengths.

CoherenceLengthSelfEnergy

Calling sequence

SimulationParameter{ CoherenceLengthSelfEnergy }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{nm}\)

Functionality

—

SpatialGridSpacing

Calling sequence

SimulationParameter{ SpatialGridSpacing }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{nm}\)

Functionality

Sets the real space grid spacing in the growth (\(z\)) direction.

Note

How should I choose the grid spacing?

Usually the layers in a QCL have thicknesses of around 1 nm, e.g. 1.3 nm and 1.7 nm. Therefore, in this case, grid spacing of 0.2 or 0.3 nm will not make a big difference in the results. This should, however, be checked for each structure. 0.2-0.3 nm is typically a reasonable number.

Note

This parameter only affects the basis state calculation time. They are not critical for the total calculation time since the NEGF self-consistent loop is usually the most time-consuming part.

nLateralPeriodsForBandStructure

Calling sequence

SimulationParameter{ nLateralPeriodsForBandStructure }

Properties

  • type: \(\mathrm{integer}\)

  • values: {0, 1, 2, 3, ...}

Functionality

Sets the number of periods next to the central period. If this parameter is N, 2N+1 periods are used in the Schrödinger equation, which is solved at the beginning of the simulation (models described in Electronic band structure). The spectrum will contain 2N+1 states per miniband. (The number of grid points) * (2N+1) should not exceed \(\sim 10^4\) for fast calculation. A large N can be used for accurate calculation of the energy levels and wave functions that are plotted in the folder EnergyEigenstates.

Note

This parameter only affects the basis state calculation time. They are not critical for the total calculation time since the NEGF self-consistent loop is usually the most time-consuming part.

Note

How many periods should I define in my QCL input file?

It is sufficient for the standard user to specify N = 1. Having more than that can be done for consistency test, but we do not see any physical interest in doing so (the calculation and convergence will only be longer). If you want to account for longer coherence length only, CoherenceLengthInPeriods can be increased.

The gain spectra should be independent of the number of periods since the material gain is averaged over one period.

SmoothingLengthKP

Calling sequence

SimulationParameter{ SmoothingLengthKP }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{nm}\)

Functionality

—

ContinuousValenceBand

Calling sequence

SimulationParameter{ ContinuousValenceBand }

Properties

  • choices: yes; no

  • default: no

Functionality

Switches between two different discretization schemes when NumberOfBands is 8.

EnergyRangeAxial

Calling sequence

SimulationParameter{ EnergyRangeAxial }

Properties

  • type: \(\mathrm{real\;number}\)

  • unit: \(\mathrm{meV}\)

Functionality

Sets a energy cut-off for the mode selection in the conduction band along the growth axis (\(z\) direction). It is evaluated from the lowest energy state in the conduction band.

Note

This choice is critical for the NEGF calculation time: the axial energy range needs to be large enough to cover all relevant carrier dynamics, but small enough to save computation time.

EnergyRangeAxialValence

Calling sequence

SimulationParameter{ EnergyRangeAxialValence }

Properties

  • type: \(\mathrm{real\;number}\)

  • unit: \(\mathrm{meV}\)

Functionality

Sets a energy cut-off for the mode selection in the valence band along the growth axis (\(z\) direction). It is evaluated from the highest energy state in the valence band.

Note

This choice is critical for the NEGF calculation time: the axial energy range needs to be large enough to cover all relevant carrier dynamics, but small enough to save computation time.

NumberOfConductionSubbands

Calling sequence

SimulationParameter{ NumberOfConductionSubbands }

Properties

  • type: \(\mathrm{integer}\)

  • values: {0, 1, 2, 3, ...}

Functionality

Specifies the number of subbands for the mode selection in the conduction band.

Note

This choice is critical for the NEGF calculation time: the axial energy range needs to be large enough to cover all relevant carrier dynamics, but small enough to save computation time.

NumberOfValenceSubbands

Calling sequence

SimulationParameter{ NumberOfValenceSubbands }

Properties

  • type: \(\mathrm{integer}\)

  • values: {0, 1, 2, 3, ...}

Functionality

Specifies the number of subbands for the mode selection in the valence band.

Note

This choice is critical for the NEGF calculation time: the axial energy range needs to be large enough to cover all relevant carrier dynamics, but small enough to save computation time.

AssumeIntrinsicNeutrality

Calling sequence

SimulationParameter{ AssumeIntrinsicNeutrality }

Properties

  • choices: yes; no

  • default: no

Functionality

Only relevant if NumberOfBands is 8 and valence band states are selected. If yes, calculate the initial background density by summing up the states between the lowest selected axial energy and the 6N-th eigenvalue of the Hamiltonian, where N is the total number of real space grid points. If no, calculate it by summing up the states from the bottom of the full spectrum up to the lower axial energy cut-off.

EnergyRangeLateral

Calling sequence

SimulationParameter{ EnergyRangeLateral }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{meV}\)

Functionality

Sets the energy range of the in-plane dispersion. The energy reference is the bottom of the ground states.

Note

This choice is critical for the NEGF calculation time: the in-plane energy range needs to be large enough to cover all relevant carrier dynamics, but small enough to save computation time.

EnergyGridSpacing

Calling sequence

SimulationParameter{ EnergyGridSpacing }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • unit: \(\mathrm{meV}\)

Functionality

Sets the homogeneous energy grid spacing for the Green’s functions and self-energies.

Note

This choice is critical for the NEGF calculation time: the energy grid needs to be fine enough to resolve the peaks of the Green’s functions, but coarse enough to save computation time. Higher temperature leads to larger broadening, in which case fewer energy grid points are sufficient.

EminShift

Calling sequence

SimulationParameter{ EminShift }

Properties

  • type: \(\mathrm{real\;number}\)

  • unit: \(\mathrm{meV}\)

Functionality

Shifts the lower bound of the energy range for the Green’s functions. Negative value increases the energy range. See Energy range of the Green’s functions for details.

EmaxShift

Calling sequence

SimulationParameter{ EmaxShift }

Properties

  • type: \(\mathrm{real\;number}\)

  • unit: \(\mathrm{meV}\)

Functionality

Shifts the upper bound of the energy range for the Green’s functions. Positive value increases the energy range. See Energy range of the Green’s functions for details.

EnergyReference

Calling sequence

SimulationParameter{ EnergyReference }

Properties

  • type: \(\mathrm{real\;number}\)

  • unit: \(\mathrm{eV}\)

Functionality

—

ConvergenceValueGF

Calling sequence

SimulationParameter{ ConvergenceValueGF }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

Functionality

Sets the target relative residue for the Green’s functions.

Note

Small values for the convergence values, together with sufficiently large NMaxIterations, will give the most accurate results.

ConvergenceMinimum

Calling sequence

SimulationParameter{ ConvergenceMinimum }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

Functionality

—

ConvergenceValueCurrent

Calling sequence

SimulationParameter{ ConvergenceValueCurrent }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

Functionality

Sets the target relative residue for the current density.

Note

Small values for the convergence values, together with sufficiently large NMaxIterations, will give the most accurate results.

ConvergenceValueNorm

Calling sequence

SimulationParameter{ ConvergenceValueNorm }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • default: 0.1

Functionality

In charge-neutral device, if the charge density deviates from the doping density relatively by more than this value, stay in the Self-consistent iteration loop. This is to ensure charge conservation.

NMaxIterations

Calling sequence

SimulationParameter{ NMaxIterations }

Properties

  • type: \(\mathrm{integer}\)

  • values: {1, 2, 3, 4, ...}

Functionality

Sets the maximum number of NEGF iterations.

Note

Small values for the convergence values, together with sufficiently large NMaxIterations, will give the most accurate results.

ConvergFactInit

Calling sequence

SimulationParameter{ ConvergFactInit }

Properties

  • type: \(\mathrm{real\;number}\)

Functionality

—

ConvergFactMin

Calling sequence

SimulationParameter{ ConvergFactMin }

Properties

  • type: \(\mathrm{real\;number}\)

Functionality

—

ConvergFactMax

Calling sequence

SimulationParameter{ ConvergFactMax }

Properties

  • type: \(\mathrm{real\;number}\)

Functionality

—

ExitLoopIfNoConvergAfter

Calling sequence

SimulationParameter{ ExitLoopIfNoConvergAfter }

Properties

  • type: \(\mathrm{integer}\)

  • values: {1, 2, 3, 4, ...}

Functionality

—

PhononConvergence

Calling sequence

SimulationParameter{ PhononConvergence }

Properties

  • type: \(\mathrm{real\;number}\)

  • —

Functionality

—

MagneticField

Calling sequence

SimulationParameter{ MagneticField }

Properties

  • type: \(\mathrm{real\;number}\)

  • —

Functionality

—

NMaxThreads

Calling sequence

SimulationParameter{ NMaxThreads }

Properties

  • type: \(\mathrm{integer}\)

  • values: {1, 2, 3, 4, ...}

Functionality

Sets the maximum number of threads to be used for openMP parallelization of the calculation of Green’s functions, self-energies, and other linear algebra.

Warning

This setting is overridden if the command line parameter --threads (Command Line) exists.

StartFromEquilibrium

Calling sequence

SimulationParameter{ StartFromEquilibrium }

Properties

  • choices: yes; no

  • default: no

Functionality

StartFromPrevious

Calling sequence

SimulationParameter{ StartFromPrevious }

Properties

  • choices: yes; no

  • default: no

Functionality

—

BroadenLevels

Calling sequence

SimulationParameter{ BroadenLevels }

Properties

  • type: \(\mathrm{real\;number}\)

  • values: [0.0, ...)

  • —

Functionality

—

Last update: 28/10/2024