# Parameters for calculating transmission coefficients

Parameters here are for calculating the transport coefficients of quantum transport.

## calculation.transmission.method

keyword: calculation.transmission.method

possible values: ‘GreenFunction’ or ‘WaveFunction’

default value: ‘GreenFunction’

description: method used for the calculation of the transmission coefficient.

an example:

```calculation.transmission.method = 'GreenFunction'
```

possible values: cell array of 1 x 2 integer array

default value: all pairs of leads

description: For each pair of leads in the cell, the transmission from the first lead of the pair to the second lead is to be calculated.

an example:

```calculation.transmission.leadPairs = {[1,2], [2,1]}
```

## calculation.transmission.kSpaceGridNumber

keyword: calculation.transmission.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.transmission.kSpaceGridNumber = [10 10 10]'
```

## calculation.transmission.kSpaceGridShift

keyword: calculation.transmission.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 transmission.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.transmission.kSpaceGridShift = [1/2 1/2 1/2]'
```

## calculation.transmission.energyPoints

keyword: calculation.transmission.energyPoints

possible values: double array

default value: chemical potentials of all the leads.

description: the energy points at which the transmission will be calculated. Note that the energy values are measured from chemical potential of a lead having zero applied voltage.

an example:

```calculation.transmission.energyPoints = 0
```

## calculation.transmission.eta

keyword: calculation.transmission.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 transmission.etaSigma and/or transmission.etaGF is not given.

an example:

```calculation.transmission.eta = 1e-4
```

## calculation.transmission.epsilon

keyword: calculation.transmission.epsilon

possible values: a small double number

default value: 1e-9

description: used as a criterion to decide if a state is a Bloch wave. For a wave with wave-vector k, if ||exp(ika)|-1| < epsilon, where a is the unit cell length, it is considered as a Bloch wave; otherwise it is considered as an evanescent wave.

an example:

```calculation.transmission.epsilon = 1e-4
```

## calculation.transmission.plot

keyword: calculation.transmission.plot

possible values: true or false

default value: false

description: If true, a plot will be given after the calculation.

an example:

```calculation.transmission.plot = true
```