Parameters for calculating acConductance
Parameters here are for calculating the frequency dependent conductance. When an AC bias is applied to the device, frequency dependent transport properties are important. At high AC frequency, induction produces displacement currents which must be taken into account.
calculation.acConductance.maximumFrequency
keyword: calculation.acConductance.maximumFrequency
possible values: a double number
default value: 10 THz
description: the ac conductance is calculated as a function of frequency from zero up to this value. The unit is MHz.
an example:
calculation.acConductance.maximumFrequency = 1000000
calculation.acConductance.numberOfFrequencyPoints
keyword: calculation.acConductance.numberOfFrequencyPoints
possible values: an integer number
default value: 101
description: number of the frequency points at which the ac conductance is calculated.
an example:
calculation.acConductance.numberOfFrequencyPoints = 501
calculation.acConductance.temperature
keyword: calculation.acConductance.temperature
possible values: a double value
default value: the value used in the calculation of the self-consistent Hamiltonian, or 0 if an user provided Hamiltonian is used.
description: temperature used in the Fermi function when calculating the acConductance, in unit of Kelvin. Note: the Boltzmann constant k = 8.617342e-05(eV/K) = 3.1668151e-06 (Hartree/K).
an example:
calculation.acConductance.temperature = 100
calculation.acConductance.kSpaceGridNumber
keyword: calculation.acConductance.kSpaceGridNumber
possible values: 3 x 1 integer array
default value: the value of calculation.k_spacegrids.number which was used in the Hamiltonian calculation, or [1 1 1] if an user provided Hamiltonian is used.
description: number of small k-space grids in each direction which, together with kSpaceGridShift, are used to produce the parameter kSpacePoints.
an example:
calculation.acConductance.kSpaceGridNumber = [10 10 10]'
calculation.acConductance.kSpaceGridShift
keyword: calculation.acConductance.kSpaceGridShift
possible values: 3 x 1 or 1 x 3 array, [s_1, s_2, s_3], with each s_i a double number between 0 and 1.
default value: if the acConductance.kSpaceGridNumber is given, or if an user provided Hamiltonian is used, the default value is [0 0 0], otherwise the default value is the value of calculation.k_spacegrids.shift which was used in the Hamiltonian calculation.
description: k-space grid point shift. While all s_i are set to be 0, the Gamma point is always among the k-space grid points being generated; otherwise, the k-space grid points will be shifted s_1, s_2, and s_3 grid lengths along their grid vector directions, respectively.
an example:
calculation.acConductance.kSpaceGridShift = [1/2 1/2 1/2]'
calculation.acConductance.kSpacePoints
keyword: calculation.acConductance.kSpacePoints
possible values: 3 x n double array
default value: defined in the k-point file if the file is given by the parameter acConductance.kPointFile, or produced by the parameters acConductance.kSpaceGridNumber and acConductance.kSpaceGridShift.
description: the fractional coordinates of n transverse wavevectors which are used in the k-space integration.
an example:
calculation.acConductance.kSpacePoints = [0 0 0]'
calculation.acConductance.kPointWeights
keyword: calculation.acConductance.kPointWeights
possible values: 1 x n double array
default value: defined in the k-point file if the corresponding parameter acConductance.kSpacePoints is using the k-values in the same file. Otherwise, equally weighted.
description: the weights of the k-space points in the k-space integration.
an example:
calculation.acConductance.kPointWeights = [1/2 1/3 1/6]
calculation.acConductance.kPointFile
keyword: calculation.acConductance.kPointFile
possible values: a file name
default value: no default value
description: the name of a file which contains the coordinates of k-space points and their corresponding weights.
A k-point file with n k-points has (n+1) lines: one line of headers and n lines of values of the n k-points. The headers are:
number : sequential number of the k-point k1, k2, k3 : fractional coordinates of the k-point divisor : used to modify k1, k2, and k3 so that the real fractional coordinates are k1/divisor, k2/divisor, k3/divisor weight : relative weights of the k-points for the k-space integration. Normalized so that sum(weight) = 1.
where the headers number, divisor, and weight are optional. The following is an example of the file.
number k1 k2 k3 divisor weight 1 0 0 0 7 1.0 2 0 1 0 7 2.0 3 0 2 0 7 2.0 4 0 3 0 7 2.0 5 1 0 0 7 2.0 6 1 1 0 7 4.0 7 1 2 0 7 4.0 8 1 3 0 7 4.0 9 2 0 0 7 2.0 10 2 1 0 7 4.0 11 2 2 0 7 4.0 12 2 3 0 7 4.0 13 3 0 0 7 2.0 14 3 1 0 7 4.0 15 3 2 0 7 4.0 16 3 3 0 7 4.0
an example:
calculation.acConductance.kPointFile = 'k-points.dat'
calculation.acConductance.numberOfEnergyPoints
keyword: calculation.acConductance.numberOfEnergyPoints
possible values: an integer number
default value: determined by parameter energyInterval
description: the number of energy points used in the energy space integration.
an example:
calculation.acConductance.numberOfEnergyPoints = 100
calculation.acConductance.energyInterval
keyword: calculation.acConductance.energyInterval
possible values: a double number
default value: minmum(50meV, maximum(5meV, kT))
description: Energy interval used to determine the parameter numberOfEnergyPoints.
an example:
calculation.acConductance.energyInterval = 1e-3
calculation.acConductance.etaSigma
keyword: calculation.acConductance.etaSigma
possible values: a small double number
default value: 1e-6 Hartree
description: the small eta used in the calculation of self-energy when the ‘GreenFunction’ method is chosen.
an example:
calculation.acConductance.etaSigma = 1e-4
calculation.acConductance.etaGF
keyword: calculation.acConductance.etaGF
possible values: a small double number
default value: 0
description: the small eta used in the calculation of Green’s function when the ‘GreenFunction’ method is chosen.
an example:
calculation.acConductance.etaGF = 1e-4
calculation.acConductance.eta
keyword: calculation.acConductance.eta
possible values: a small double number
default value: no default value
description: the small eta used in the calculation of self-energy and/or Green’s function when the ‘GreenFunction’ method is chosen. This parameter is only used when the parameter acConductance.etaSigma and/or acConductance.etaGF is not given.
an example:
calculation.acConductance.eta = 1e-4
calculation.acConductance.plot
keyword: calculation.acConductance.plot
possible values: true or false
default value: false
description: If true, a plot will be given after the calculation.
an example:
calculation.acConductance.plot = true