# current calculation

Hi,

i am having some confusion regarding current in the tbtrans output file and transmission values.

For a spin polarized transport calculation i am getting spin down current more than spin up current from the output file. But integrating area over .AVTRANS plot spin up curve gives more value than spin down curve which is in contradiction to the output current value.

Is it possible to calculate current manually using .AVTRANS output values ?

## Question information

- Language:
- English Edit question

- Status:
- Solved

- For:
- Siesta Edit question

- Assignee:
- No assignee Edit question

- Solved by:
- Nick Papior

- Solved:
- 2019-10-18

- Last query:
- 2019-10-18

- Last reply:
- 2019-10-17

Nick Papior (nickpapior) said : | #1 |

You can implement Eq. 30 in https:/

Note that the AVTRANS already contains the k-averaged transmission so you'll drop one of the integrals.

Thank you for the reply.

Which output file has to consider the integral of the other parameter in the equation(ie n(E)) ?

Hi Nick,

Which range of energy has to be considered while calculating current manually using the equation?

Nick Papior (nickpapior) said : | #4 |

The range of energies depends on the fermi-function differences.

So it depends on the chemical potentials and the temperatures. Typically I integrate between -5 kT + mu_low TO mu_high + 5 kT.

Thanks for the reply.

To calculate current I have multiplied the corresponding k averaged transmission and DOS and integrated it over a certain energy range. Is this the right method?

Whether it is required to multiply by any factor?

For e and h whether the actual value has to be substituted or is it considering as 1?

Nick Papior (nickpapior) said : | #6 |

No, it is not the correct method (the DOS does not enter the equation). Please use the equation I referenced previously.

Thanks Nick Papior, that solved my question.